| title: | Charge and Wavelength Scaling of RF Photoinjector Designs |
| format: | |
| year published: | September 21, 1994 |
| year authored: | 1994 |
| authors: | J. Rosenzweig,E. Colby |
| abstract: | The optimum design of an emittance compensated rf photoinector is very complicated and time-consuming, relying heavily on multi-particle simulations without good analytical models as a guide. Emittance compensated designs which have been developed, however, can be used to generate other designs with no additional effort if the original design is scaled correctly. This paper examines the scaling of rf photoinjector design with reqpect to charge and wavelength, and presents emittance and brightness scaling laws for these variables. Parametric simulation studies are presented to illustrate these scaling laws. Deviations from scaling and practical considerations are also discussed. |
| title: | On Some Distinctiveness of the Kurchatov-UCLA Undulator Scheme Providing Strong Magnetic Fields for Short Periods |
| format: | |
| year published: | September 1991 |
| year authored: | 1991 |
| authors: | C. Pellegrini,A. Varfolomeev |
| abstract: | We present a qualitative analysis of the new scheme for the Kurchatov large field strengh short period undulator installed at UCLA and compare it with some hybrid schemes suggested by other laboratories. We show that beyond the apparent similarity important differences exist between these devices. As a result our design provides a higher saturation limit for the undulator magnetic fields. |
| title: | High Brightness Symmetric Emittance RF Photoinjector Preliminary Design Report |
| format: | unpublished |
| year published: | September 15, 1994 |
| year authored: | 1994 |
| authors: | E. Colby,J. Ostiguy,J. Rosenzweig |
| abstract: | A preliminary design for a high bunch charge (8 nC), low emittance (> 20 mm-mr) radiofrequency electron photoinjector matched to the requirements of the Tesla Test Facility is presented. A 1.5 cell iris coupled pi-mode structure with high average accelerating gradient is chosen for its high shunt impedance, simplicity, and ability to accommodate an externally mounted solenoid for simultaneous beam divergence control an demittance compensation. Beam optics are optimized for an overall injector consisting of the electron gun followed by one linac capture section, a dipole chicane for magnetic bunch compression to achieve a bunch length corresponding to sigma_z = 1 mm. Electrical and beam dynamical aspects of the photoinjector design are presented. A description of the proposed experimental program is included. |
| title: | Modeling of the X-ray Radiation Dependence on Power in High Gradient Radio-frequency Accelerator Structures |
| format: | unpublished |
| year published: | October 9, 1995 |
| year authored: | 1995 |
| authors: | D. Gooden,J. Rosenzweig |
| abstract: | It has long been known that field-emitted (FE) electron current is what generates the x-ray radiation from high-power RF accelerating strucutures, but it has not yet been qualitatively understood how the radiation varies with the microwave power input to these structures. This paper will show that from successive measurements of the RF power at a single position and the corresponding radiation dose rate ... |
| title: | Analogies Between Charged Particle Beams and Photon Beams: Simple Methods for Laboratory Use |
| format: | unpublished |
| year published: | October 25, 1991 |
| year authored: | 1991 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | 3.5 Cell R.F. Gun Simulation with Spacecharge and Focusing Coil U.C.L.A. IRFEL Note H.1 |
| format: | unpublished |
| year published: | November 9, 1989 |
| year authored: | 1989 |
| authors: | S. Hartman |
| abstract: | Using the particle simulation code PARMELA, I calculated the emittance values for a three and one half cell gun. Since the beam suffers a R.F. defocusing at the exit of the last cell a solenoidal focusing element was added to cancel the divergence effect. |
| title: | The VISA FEL: an ultra-short gain length, saturated, self-amplified spontaneous emission free-electron laser |
| format: | unpublished |
| year published: | May 31, 2002 |
| year authored: | 2002 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | Monitoring and Manipulation of Sub-picosecond Beams |
| format: | unpublished |
| year published: | May 30, 2002 |
| year authored: | 2002 |
| authors: | J. Rosenzweig |
| abstract: | Outline: Applications of sub-picosecond beams: a UCLA-centric view Sub-picosecond beam generation Sub-picosecond beam manipulation Sub-picosecond beam diagnosis The future |
| title: | Velocity Bunching: ORION, PLEIADES and NEPTUNE |
| format: | unpublished |
| year published: | May 3, 2002 |
| year authored: | 2002 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | SUPERFLIC - A Recirculating Superconducting Linear Collider Top Factory |
| format: | unpublished |
| year published: | May 28, 1991 |
| year authored: | 1991 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | Towards Short Wavelength FELs Workshop: Highlights and Implications for PBPL |
| format: | |
| year published: | May 1993 |
| year authored: | 1993 |
| authors: | G. Travish |
| abstract: | A two day meeting was h eld at Brookhaven (May 21, 22) to discuss the future of short wavelenght FEL work. Various groups presented current work, next step plans and future proposals. Working groups were formed to do paper designs of a facility to produce ~1000A light at significant power levels. All designs attempted to use existing hardware. Final designs were all estimated to cost over $5M. This has significant implications for the future of FEL experimetns. It was also agreed that existing facilities should be supported in order to obtain useful results as soon as possible. This has significant and positive implications for the UCLA experiments. |
| title: | Faraday Cup Beam Dumps for the UCLA PBPL |
| format: | tech note |
| year published: | May 16, 1994 |
| year authored: | 1994 |
| authors: | D. McIntosh |
| abstract: | Two identical Faraday cups have been designed and built to stop a 20 meV, 1 nC electron pulse beam, accelerated at the UCLA Particle Beam Physics Laboratory (PBPL). The dumps were also designed to serve as charge measuring diagnostics. Each device is a simple design using a carbon graphite core, Delrin insulation, vacuum tubing components, and lead brick shielding. The graphite core stops the beam while producing manageable secondary radiation sources. The overall design considerations and final solutions are summarized. |
| title: | Free-Electron Simulations at Short Wavelengths |
| format: | unpublished |
| year published: | May 01, 2002 |
| year authored: | 2002 |
| authors: | S. Reiche |
| abstract: | Outline: FEL Simulations Overview Codes Shot-Noise Models Short Wavelength Effects Spontaneous Radiation Wake Fields Undulator Description Start-End Simulations |
| title: | Coherent Transition Radiation Dignosis of Microbunching at the Exit of a Free-Electron Laser Undulator |
| format: | |
| year published: | March 6, 1995 |
| year authored: | 1995 |
| authors: | J. Rosenzweig,G. Travish,A. Tremaine |
| abstract: | The action of the free-electron laser instability (FEL) on an electron beam produces a longitudinal density modulation with a periodicity near the resonant radiation wavelength. This modulation, which can produce femtosecond or shorter microbunches inside of a macroscopic picosecond electron pulse, has been proposed for use as a prebunching injector for both higher harmonic FELs and short wavelength accelerators. Standard methods involving streak cameras or beam sweeping with dipole mode cavities will certainly fail to provide information about this longitudinal microstructure, however. In this paper we explore the use of coherent transition radiation generated from a foil a the exit of an FEL undulator to diagnose both the lognitudinal and transverse electron microbunch structure. |
| title: | Accelerator and Charged Particle Beam Physics at UCLA |
| format: | unpublished |
| year published: | March 2002 |
| year authored: | 2002 |
| authors: | J. Rosenzweig |
| abstract: | Outline: What do we do? Who is involved What is current highlights of the research and education programs? Where are the future opportunities |
| title: | Design Considerations for the UCLA PBPL Slit-based Phase Space Measurement Systems |
| format: | |
| year published: | March 2, 1994 |
| year authored: | 1994 |
| authors: | J. Rosenzweig,G. Travish |
| abstract: | The phase space measurement system initially implemented by Spencer Hartmann on the UCLA PBPL rf photocathode gun has been upgraded, and a new system has been designed to measure the emittance at higher energy, after the emittance compensating drift and acceleration in the PWT linac. The purpose of this note is to describe the design criteria and physical principles involved in obtaining systems which provide the resolution in phase space measuremtns that we require. The final lit and detectro hardware designs are included; the video data acquisition and analysis will remain nearly unchanged from Hartmann's system. |
| title: | Surface Plasmon Enhanced Photoemission |
| format: | unpublished |
| year published: | March 18, 1993 |
| year authored: | 1993 |
| authors: | S. Hartman |
| abstract: | Photoemission studies have been carried out recently at the UCLA photo injector which cannot be explained by a straight forward application of the standard Fowler-Dubridge (1,2) theory for photoemission. This theory is used to calculate the contributions to the extracted current from field emission, thermal emission and the bulk photoemission process. The Fowler-Dubridge theory predicts a photoyield of 5x10(-6), which is two orders of magnitude less than that observed experimentally at 70 degrees incidence. However, if one assumes optical coupling to surface polasmons via surface roughness. Then one can calculate photoyields of 10(-4) as observed experimentally. Also, if the vector nature of the photoemission process is accounted for then one can calculated photoyields which agree with experimental data as a function of incident illumination angle, polarization angle, and laser wavelength. A few ideas are then set forth on photocathode preparation and materials so as to increase photoyield. |
| title: | Experimental Experience in High Brightness Beams and SASE FELs at UCLA |
| format: | unpublished |
| year published: | June 6, 2002 |
| year authored: | 2002 |
| authors: | J. Rosenzweig |
| abstract: | Outline: Introduction to the UCLA Particle Beam Physics Laboratory (PBPL) High Brightness Beam Generation and Manipulation SASE FELs: Experimental Results Future work at UCLA |
| title: | Redesign of the Low Energy Beam Transport in the UCLA Photoinjector |
| format: | unpublished |
| year published: | June 24, 1993 |
| year authored: | 1993 |
| authors: | J. Rosenzweig |
| abstract: | The low energy transport of the beam in teh UCLA photoinector has been the source of experimental difficulties associated with preserving the emittance and the pulse length while the beam experience large self-forces due to space charge. While some of the difficulties (most notably the pulse lengthening) can be mitigated by previous experiments, a major improvement should result from minimixing the low energy beam transport region from teh gun to the linac. |
| title: | MAFIA Studies of the Plane Wave Tranformer Linac |
| format: | unpublished |
| year published: | Januray 6, 1992 |
| year authored: | 1992 |
| authors: | S. Hartman |
| abstract: | In designing a high power rf-accelerator one needs to examine any filed disturbances created by asymmetries in teh structure. In the following we present a study of the disturbance of the modes using the three-dimensional frequency domain solver MAFIA[1]. We pay particular attention to perturbations in the accelerating mode and also to higher order modes which can be excited by the electron beam itself. These perturbations in the accelerating mode and off axis kicks due to the higher order modes give rise to emittance growth. Some ideas of how to redesign the support structure in order to iminimze accelerating mode perturbation effects and also of how to damp out unwanted higher order modes are discussed. |
| title: | 1.5 Cell R.F. Gun Simulation with coil and Space Charge U.C.L.A. IRFEL Note H.3 |
| format: | unpublished |
| year published: | January 9, 1990 |
| year authored: | 1990 |
| authors: | S. Hartman |
| abstract: | Simulations were done to explore the effect of placing a coil along the beamline to minimize the divergent lense effect of the exit of the last cell of the gun....etc. |
| title: | Report on a Visit by American Scientists to UNK Project at IHEP-Protvino |
| format: | unpublished |
| year published: | January 8, 1993 |
| year authored: | 1993 |
| authors: | M. Medinnis,C. Pellegrini,P. Schlein,A. Sessler,C. Taylor,P. Reardon |
| abstract: | This document results from a visit to the Institute for High Energy Physics in Protvino, Russia, by a group of U.S. physicists during 13-15 July, 1992. The purpose of the trip, which was supported by the U.S. National Science Foundation, was to learn about the state of the UNK superconducting 3 TeV accelerator complex and also to understand the cost and magnitude of the task required to complete the machine. If completed, UNK could provide a unique High Energy Physics facility. First, a collider version could serve as an excellent Factory to study the decay of Beauty particles. Secondly, the 3 TeV proton beam may be the highest energy available for a fixed target physics program. Although the superconducting magnet design is mature and tests have been successful, severe budget cutbacks have brought the project to a virtual halt. A realistic goal for IHEP may be the expeditious completion of UNK-1, the 600 GeV booster ring, in parallel with the pursuit of international collaboration on fiscal, technical and management support for the 3 TeV project. |
| title: | Degradation of Longitudinal Phase Space Distribution of the LCLS Beam by Compton Back-Scattering |
| format: | unpublished |
| year published: | January 24, 1993 |
| year authored: | 1993 |
| authors: | J. Rosenzweig |
| abstract: | The requirements on the phase and amplitude jitter of the photoinjector laser in teh LCLS are very stringent. These can be eased if the incoherent energy spread in the beam is increased, decreasing the sensitivity of the bunch compression process. There are few good ways of increasing the incoherent, as opposed to the coherent, energy spread, which can be easily increased by rephasing the rf, or by space charge. A radiative or a collisional process must be used to increase the incoherent energy spread, in order to make the energy change independent of phase. Here we examine the feasibility of using the back-scattering of photons from an intense, one picosecond laser beam. We assume that we can use a laser beam (1047 nm wavelength, Nd:YLF), chosen to allow it to drive both the cathode (after quadrupling), and the longitudinal phase space degrader. |
| title: | Remote Control of the Miller Power Supply |
| format: | tech note |
| year published: | January 1, 1994 |
| year authored: | 1994 |
| authors: | R. Hedrick |
| abstract: | The current for the rolenoids is provided by a Miller Synchrowave 500 Arc Welding Power Supply (MPS)..... |
| title: | Space Charge Depleted Emission and Electron Beam Pulse Lengthening from a Damaged Photocathode |
| format: | unpublished |
| year published: | February 4, 1993 |
| year authored: | 1993 |
| authors: | S. Hartman,J. Rosenzweig |
| abstract: | There have been a long-standing questions about the amount of charge extracted from the UCLA photo-injector as a function of incident laser energy (quantum efficiency), and the observed pulse lengthening in time. One expects the charge measured at the exit of the rf gun to be a linear function of applied laser energy to the photocathode. However, this is not the case for the UCLA experiment thus far. The quantum efficiencey data, which measures the total extracted charge out of the rf gun as a function of laser energy, is very non linear. From zero nC to approximately 0.5 nC the charge extracted follows a linear trend. From 0.5 nC to 3 nC the extracted charge falls off unexpectedly. In addition, streak camera measurements indicate that the beam's temporal length expands considerably from that of the laser. Because of the highly dynamical behavior of the electron beam near the cathode, a series of PARMELA simulations have been carried out to model the evolution of the beam in this region, both in time structure and in maximum allowed charge. These simulations give excellent agreement with the experimental data. Also, a simple model is put forth to explain the physical process which limits the emission of charge. |
| title: | Space Charge Depleted Emission from a Damaged Photocathode |
| format: | unpublished |
| year published: | February 4, 1993 |
| year authored: | 1993 |
| authors: | S. Hartman,J. Rosenzweig |
| abstract: | There has been a long-standing question about the amount of charge extracted from the UCLA photo-injector as a function of incident laser energy (quantum efficiency). One expects the charge measured at the exit of the rf gun to be a linear function of applied laser energy to the photocathode. However, this is not the case fo the UCLA experiment thus far. However, the quantum efficiency data which measures the total extracted charge out of the rf gun as a function of laser energy, is very non linear. From zero nC to approximately 0.5nC the charge extracted follows a linar trend. From 0.5nC to 3nC the extracted charge falls off unexpectedly. Because of the highly dynamical behaviour of the electron beam near the cathode, a series of PARMELA simulations have been carried out to model the evolution of the beam in this region. These simulations give excellent agreement with the experimental data. Also, a simple model is put forth to explain the physical process which limits the emission of charge. |
| title: | Effects of the Stray Magnetic Field Caused by a Vacuum Ion Pump on the Accelerator Beamline |
| format: | unpublished |
| year published: | February 2, 1994 |
| year authored: | 1994 |
| authors: | R. Hedrick |
| abstract: | A Vac Ion pump is often used adjacent to the accelerator beamline. Stray magnetic fields are caused by the pump's permanent magnet. The pump is attached to the beamline in one of two configurations, either parallel or perpendicular to the beam path. Moving charged particles, along the beamline, experience a force or kick due to the stray B-field which de3flects the particles away from their original trajectory. From measurements made in each configuration, the deflection angles of the particles were calculated. For a particle of low energy, 4.5 MeV, the angles calculated were approximately 1 and 12 mrad for Config. 1 and Config. 2 respectively. The calculations for high energy, 20 MeV, yielded angles of 1/5 and 3 mrad. These deflections, for Config. 1, are lower than the inherent divergence of the beam, so this configuration can be used without compromising the beam quality. The deflection due to Config. 2, at low energy, is larger than the inherent beam divergence and at high energy, it is over half of the beam divergence angle. the second configuration should not be used. |
| title: | DOE Review |
| format: | unpublished |
| year published: | February 17, 1993 |
| year authored: | 1993 |
| authors: | . |
| abstract: |
| title: | Operating Procedures for the UCLA Linear Accelerator Facility |
| format: | |
| year published: | February 14, 1991 |
| year authored: | 1991 |
| authors: | C. Pellegrini,C. Joshi |
| abstract: | An RF laser-driven electron gun is being built at UCLA. This electron injector will be used to study the production of high-brightness electron beams, and to drive a high gain, free-electron laser amplifier. Other particle beam physics experiments include plasma wakefiled acceleration. All these experiments are performed under the umbrella of the Center for Advanced Accelerators located at the UCLA Linear Accelerator Laboratory. |
| title: | PARMELA simulation of the U.C.L.A. compact linac |
| format: | unpublished |
| year published: | February 11, 1991 |
| year authored: | 1991 |
| authors: | S. Hartman |
| abstract: | The compact laser-driven R.F. linac for the SATURNUS project has been modeled using the particle dynamics simulation code PARMELA....etc. |
| title: | A Simple Calculation of Electron and Lattice Heating in the UCLA RF Photocathode |
| format: | |
| year published: | December 17, 1992 |
| year authored: | 1992 |
| authors: | J. Rosenzweig |
| abstract: | It has been suggested by C. Joshi that the source of pulse lengthening in the electon beam emitted from the UCLA rf photocathode is due to the heating of the conduction electrons in the copper by the laser pulse. The proposed mechanism for continued emission after the end of the laser is thermally enhanced field emission. Simple calculations (see below) indicate that the temperature rise associated with the laser power deposition could be, in the absence of diffusion and coupling to the ions, in excess of 1000 degrees Kelvin, a temperature which could indeed allow emission. In addition, there have been experiments on this films have shown that this elevated termperature can persist for many picoseconds after the laser is no longer on. The purpose of this note is to explore, using a simple model based on the heat equations for the electrons and the ion lattice, and an even more simplified numerical solution of these coupled differential equations, the heating, as well as the diffusion and coupling of this heat, in our cathode. |
| title: | Pulse Compression in TTF Injector II |
| format: | |
| year published: | December 13, 1994 |
| year authored: | 1994 |
| authors: | J. Rosenzweig |
| abstract: | While the description of longitudinal dynamics of a beam in an rf photoinjector is in general quite complicated, the problem is straightforward after some simplifying assumptions. It is in fact an excellent assumption, that after acceleration to moderately high energy, where the longitudinal phoase space structure is well approximated by that of a beam which has passed throught the accelerating cavities at the speed of light. Under this assumption, each electron has a final energy given by ... |
| title: | Two-Stage Chirped-Beam SASE-FEL for High Power Femtosecond X-Ray Pulse Generation |
| format: | unpublished |
| year published: | December 10, 2001 |
| year authored: | 2001 |
| authors: | C. Schroeder,J. Arthur,P. Emma,S. Reiche,C. Pellegrini |
| abstract: |
| title: | Proposal for a SASE-Free-electron laser Experiment, VISA, at the ATF Linac |
| format: | |
| year published: | April 8, 1998 |
| year authored: | 1998 |
| authors: | UCLA, BNL, LANL, LLNL,. |
| abstract: | We present a proposal of a SASE-FEL experiment, VISA, to be done at the ATF linac unsing a 4m long undulator, to study the FEL collective instability regime, including saturation, start-up, time dependence and spectral and angular characteristics of the radiation. The experiment will use a complete set of diagnostics tools to allow a detailed comparison of the experimental results with the theory and the simulation codes. The experiment is being proposed by the VISA group, BNL-LLNL-LANL-SSRL/SLAC-UCLA collaboration. The experiment is part of a program to demonstrate the feasibility of short wavelength, UV to X-ray, FELs based on teh SASE collective instability regime. This program has received the highest priority from the Birgenau panel, which has recently presented a report to DOE on future needs and development of synchrotron radiation sources in the USA. This top priority has been confirmed by the fact that the Basic Energy Sciences division of DOE has already provided the funding needed to carry our VISA. |
| title: | Cold Test Measurements of the UCLA Photo-Injector |
| format: | unpublished |
| year published: | April 30, 1993 |
| year authored: | 1993 |
| authors: | S. Hartman,M. Hogan |
| abstract: |
| title: | The Photocathode Gun: Shunt Impedance and Field Balance |
| format: | unpublished |
| year published: | April 26, 1993 |
| year authored: | 1993 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | Gain Computation |
| format: | unpublished |
| year published: | April 24, 2002 |
| year authored: | 2002 |
| authors: | S. Reiche |
| abstract: |
| title: | Comparison of the FEL and CSR Instabilities |
| format: | unpublished |
| year published: | April 19, 2002 |
| year authored: | 2002 |
| authors: | S. Reiche |
| abstract: | FEL and CSR instabilities have same principle of interaction between electron beam and synchrotron radiation, but the signature is different for the different longitudinal scales. Beside the FEL these instabilities are regarded as degrading affects on the beam properties, imposing limitation on the operation range of the accelerator. |
| title: | Microwave Systems for Photocathode Gun and RF Linac at UCLA |
| format: | |
| year published: | April 16, 1991 |
| year authored: | 1991 |
| authors: | S. Park |
| abstract: | This note describes the rf systems starting from the locked laser's crystal oscillator to 20MW of microwave output from the klystron. Details on high power waveguide components[1], modulator[2], and control diagnostics can be found elsewhere. The main emphasis will be on the frequency multiplier and preamplifier to the klystron. These two systems are to accomplish two objectives: (1) Synchronize, or phase lock, the operation of laser and rf systems; (2) Provide input signal for klystron with proper frequency and power. |
| title: | Status of the Kurchatov Undulator, April 15, 1991 |
| format: | unpublished |
| year published: | April 15, 1991 |
| year authored: | 1991 |
| authors: | . |
| abstract: |
| title: | Short Pulse and Diagnostic Beamline Characteristics |
| format: | unpublished |
| year published: | April 10, 1991 |
| year authored: | 1991 |
| authors: | J. Rosenzweig |
| abstract: |
| title: | Electon Micrographs of Copper Photocathodes |
| format: | |
| year published: | April 1, 1993 |
| year authored: | 1993 |
| authors: | J. Rosenzweig |
| abstract: | Electron micrographs of both the damaged copper photocathode from the initial (September 92/April 93) run, a new unannealed cathode, and the new annealed and polished photocathode were obtained to characterize the photoemitting surfaces. These micrographs were produced by a scanning electron microscope (Cambridge (now owned by Leica) model Stereoscan 250) in the materials science department. The samples were held in place with a stainless steel holder with set screws, which allowed good electrical contact and the ability to rotate the cathodes to large angle with respect to vertical. These micrographs were performed with the idea of quantifying relevant surface features wich could be important in such phenomena as electric field enhancement, anomalous absorption of laser light, and surface plasmon excitation. |
| title: | Space Charge Depleted Emission II: Further Exploration of the Model, and Comparison to Experiment |
| format: | unpublished |
| year published: | April 1, 1993 |
| year authored: | 1993 |
| authors: | S. Hartman,J. Rosenzweig |
| abstract: | In a previous note (CAA-TEC-NOTE-48), we presented theory and simulation of space charge suppression of the emitted beam charge in from gun. The simple theory, based on calculation of the longitudiinal electric field of the beam and its image charge at teh cathode, explained both the data and the simulation well. The saturation phenomenon of the emitted beam chartge was found to depend only on the applied electric field and the effective emission area of the photoelectrons. The purpose of this note is to further explore the applicability of this theoretical model, and to show that the 70 degree quantum efficiency data quantitatively support the model. |
| title: | Solenoid Field Measurements |
| format: | tech note |
| year published: | April 1, 1991 |
| year authored: | 1991 |
| authors: | S. Hartman |
| abstract: |
| title: | CAMAC Educational Material |
| format: | unpublished |
| year published: | 7/22/1991 |
| year authored: | 1991 |
| authors: | . |
| abstract: | This handout contains copies of mini-tutorials from various company catalogs. The two introductions to the CAMAC standard are worth while reading for all group members. The two GPIB reviews are useful for anyone using or planning on using GPIB instruments. Finally, a handy glossary is attached. |
| title: | An Inverse Compton Scattering Radiation Source via Self-Guiding in a Plasma |
| conference: | |
| year: | 2006 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: | In an inverse-Compton scattering source, in which a relativistic electron beam collides with a high-power laser pulse, the x-ray flux produced is proportional to the brightness of the two beams and the size of their overlap region in three-dimensional space. In vacuum, this overlap is limited by the diffraction of the two beams, but the diffraction limit can be overcome by confining both beams in a plasma guiding channel. A dense, bunched electron beam injected into an underdense plasma will self-guide via ``blowout,'' in which the beam head creates a focusing ion channel through which the body of the beam is guided; this same channel can also guides a counterpropagating laser beam. Constraints include the need for long laser wavelength (1 to 10 µm) and high beam densities. We present a possible configuration for a gamma-ray source using 180° Compton scattering in a uniform plasma, including 2D simulation results. Estimated photon yields are up to a factor of 5 larger than in vacuum scattering, with production of nearly 1010 photons per nanocoulomb of electron beam charge. |
| title: | Beam Dynamics in a Hybrid Standing Wave-Traveling Wave Photoinjector |
| conference: | |
| year: | 2006 |
| authors: | J.B Rosenzweig,D. Alesini,A.Boni A.Boni,M. Ferrario,L. Ficcadenti,A.Fukusawa A.Fukusawa,A.Mostacci A.Mostacci,B.O’Shea B.O’Shea,L. Palumbo,B.Spataro B.Spataro,V.Fusco V.Fusco |
| abstract: | We discuss the dynamics of of a photoinjector beam in a hybrid traveling wave-standing wave photoinjector. With the field profile deduced from electromagnetic simulations, it is seen that the acceleration program induces strong velocity bunching. The beam dynamics in this scenario are explored using UCLA PARMELA. With a solenoid field overlaid on the TW section one may control emittance oscillations during bunching and acceleration. It is seen that the S-band device currently under development at UCLA may produce a 1 nC, 21 MeV, 100 micron rms pulse length beam, with emittance of 3 mm-mrad. Applications of this beam for creating coherent radiation are discussed. |
| title: | Beam compression experiments using the UCLA/ATF compressor |
| conference: | |
| year: | 2006 |
| authors: | J.B ROSENZWEIG,M. DUNNING,E. HEMSING,G. ANDONIAN,A.M COOK,A. MUROKH,S. REICHE,D. SCHILLER,M. BABZIEN,K. KUSCHE,V. YAKIMENKO,L. PALUMBO,C. VICARIO |
| abstract: | We review recent experimental results from the BNL ATF using the compressor built by UCLA. The measurements discussed include: first observation of short wavelength coherent edge radiation angular/wavelength spectrum and spectrum, sub-100 fsec pulse-length coherent transition autocorrelation measurements, and longitudinal and transverse phase space distortions. Extension of these measurements, as well as those which can be made possible by a new X-band traveling wave deflector being developed in an industrial collaboration, are examined. |
| title: | EXPERIMENTAL TESTING OF DYNAMICALLY OPTIMIZED PHOTOELECTRON BEAMS |
| conference: | Erice 2005 |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | J.B ROSENZWEIG,A.M COOK,M. DUNNING,R.J ENGLAND,P. MUSUMECI,M. BELLAVEGLIA,M. BOSCOLO,L. CATANI,A. CIANCHI,G. PIRRO,M. FERRARIO,D. FILLIPETTO,G. GATTI,L. PALUMBO,L. SERAFINI,C. VICARIO,S. JONES |
| abstract: | We discuss the design of and initial results from an experiment in space-charge dominated beam dynamics which explores a new regime of high-brightness electron beam generation at the SPARC (located at INFN-LNF, Frascati) photoinjector. The scheme under study employs the natural tendency in intense electron beams to configure themselves to produce a uniform density, giving a nearly ideal beam from the viewpoint of space charge-induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation, We show that the existing infrastructure at SPARC is nearly ideal for the proposed tests, and that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time-dependent, aerogel-based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded |
| title: | Experiment to Measure Ramped Electron Bunches at the UCLA Neptune Laboratory Using a Transverse Deflecting Cavity |
| conference: | 12th Advanced Accelerator Concepts Workshop |
| year: | 2006 |
| authors: | R. England,D. Alesini,B. O'Shea,J. Rosenzweig,and Travish |
| abstract: | A proof of principle experiment is underway at the UCLA Neptune laboratory to test the concept of generating linearly ramped relativistic electron bunches (rising in density from head to tail followed by a sharp cutoff) by using a sextupole-corrected dogleg section as a bunch compressor. Bunches with this structure have been predicted to be ideal for use as a plasma wake-field drive beam. The diagnostic being developed to measure the time profile of the beam is an X-Band (9.6 GHz) deflecting cavity. The recently completed cavity is a 9-cell standing wave structure operating in a TM110-like mode, designed to measure the temporal structure of the 2 to 10 ps, 14 MeV electron bunches generated by the Neptune S-band photoinjector and plane-wave transformer (PWT) accelerator beamline, with 50 fs resolution. We discuss the experimental plan for the ramped bunch experiment and present preliminary data related to the tuning and operation of the deflecting cavity. |
| title: | LIMITS ON PRODUCTION OF NARROW BAND PHOTONS FROM INVERSE COMPTON SCATTERING |
| conference: | |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | J.B ROSENZWEIG,A.M COOK,M. DUNNING,R.J ENGLAND,P. MUSUMECI,M. BELLAVEGLIA,M. BOSCOLO,L. CATANI,A. CIANCHI,G. PIRRO,M. FERRARIO,D. FILLIPETTO,G. GATTI,L. PALUMBO,L. SERAFINI,C. VICARIO,S. JONES |
| abstract: | In using the inverse Compton scattering (ICS) interaction as a high brilliance, short wavelength radiation source, one collides two beams, one an intense laser, and the other a high charge, short pulse electron beam. In order to maximize the flux of photons from ICS, one must focus both beams strongly, which implies both use of short beams and the existence of large angles in the interaction. One aspect of brilliance is the narrowness of the wavelength band emitted by the source. This paper explores the limits of ICS-based source brilliance based on inherent wavelength broadening effects that arise due to focal angles, laser energy density, and finite laser pulse length effects. It is shown that for a nominal 1% desired bandwidth, that one obtains approximately one scattered photon per electron in a head-on collision geometry. |
| title: | Limits on production of narrow band photons from inverse Compton scattering |
| conference: | |
| year: | 2006 |
| authors: | J. Rosenzweig,O. Williams |
| abstract: | In using the inverse Compton scattering (ICS) interaction as a high brilliance, short wavelength radiation source, one collides two beams, one an intense laser, and the other a high charge, short pulse electron beam. In order to maximize the flux of photons from ICS, one must focus both beams strongly, which implies both use of short beams and the existence of large angles in the interaction. One aspect of brilliance is the narrowness of the wavelength band emitted by the source. This paper explores the limits of ICS-based source brilliance based on inherent wavelength broadening effects that arise due to focal angles, laser energy density, and finite laser pulse length effects. It is shown that for a nominal 1% desired bandwidth, that one obtains approximately one scattered photon per electron in a head-on collision geometry |
| title: | RESULTS FROM THE UCLA/FNPL UNDERDENSE PLASMA LENS EXPERIMENT |
| conference: | Erice 2005 |
| year published: | 2006 |
| year authored: | 2005 |
| authors: | M. THOMPSON,H. BADAKOV,J. ROSENZWEIG,G. TRAVISH,H. EDWARDS,R. FLILLER,G. KAZAKEVICH,P. PIOT,J. SANTUCCI,J. LI,R. TIKHOPLAV |
| abstract: | A gaussian underdense plasma lens with peak density 5 x 1012 cm?3 and a full width half maximum (FWHM) length of 2.2 cm has been used to focus a relativistic electron beam. This plasma lens is equivalent in strength to a quadrupole magnet with a 150 T/m field gradient. The lens focused a 15 MeV, 16 nC electron beam with initial dimensions ?x,y ? 650 µm and ?z ? 6.5 mm onto an optical transition radiation (OTR) screen ?2 cm downstream of the lens. The average transverse area of the plasma focused electron beam was typically demagnified by a factor of 23. The evolution of the beam envelope in the area near the beam waist was measured for both round beams and asymmetric beams with x:y aspect ratios as large as 1:5. The light from the OTR screen in the round beam case was alsoimaged into a streak camera in order to directly measure the correlation between z and ?r within the beam. |
| title: | RF Design of the UCLA/INFN Hybrid SW/TW Photoinjector |
| conference: | |
| year: | 2006 |
| authors: | Brendan O'Shea,J.B Rosenzweig,Alessandro Boni,Atsushi Fukasawa,David Alesini,Massimo Ferrario,Bruno Spataro,Luca Ficcadenti,Andrea Palumbo |
| abstract: | With increasing demand for high brightness, low emittance beams for use with freeelectron lasers, Compton scattering systems and wake-field accelerator experiments, stringent requirements have been placed on the design and operation of the 1.6 cell photoinjector. The proposed hybrid photoinjector combines the BNL/UCLA/SLAC style 1.5/1.6 cell standing wave gun with a traveling wave accelerator. Our goal is an injector that meets today’s requirements and is scalable in design to meet tomorrow’s demands: emittances in the region of 1 mm-mrad for higher brightness as well as higher currents. The hybrid photoinjector also offers higher energy operation, enhanced cost effectiveness and better scalability than current designs such as integrated PWT photoinjectors and split gun/accelerating sections. The use of both SWand TWsystems allows for higher gradients (Eo = 70 MV/m) in the SW gun for effective capture at lower emittances, while the lower energy acceleration in the TW sections (Eo = 13.5 MV/m) allows generation of higher energy beams which are less sensitive to space charge effects. We note the current results of simulation of beam dynamics, εn,x = 3 mm-mrad, an energy spread of 1.5% with beam energies of 21 MeV at currents as high as 1.2 kA. Further we explore the possibilities of scalability to higher frequencies, analysis of coupling design, present cold test preparations and simulated RF analysis of the structure. |
| title: | Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system |
| journal: | Physical Review Special Topics - Accelerators and Beams |
| vol-pages: | 8:072401 |
| year: | 2005 |
| authors: | J. Lim,P. Frigola,G. Travish,J. Rosenzweig,S. Anderson,W. Brown,J. Jacob,C. Robbins,A. Tremaine |
| abstract: | Advanced high-brightness beam applicaitons such as inverse-Compton scattering (ICS) depend on achieving of ultra-small spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing-systems using high field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication and experimental procedure in creating ultra-small beams at PLEIADES. |
| title: | Creation of plasma density transitions short compared to the plasma skin-depth |
| journal: | REVIEW OF SCIENTIFIC INSTRUMENTS |
| vol-pages: | 76:013303 |
| year: | 2005 |
| authors: | M. Thompson,J. Rosenzweig,G. Travish |
| abstract: | A plasma based electron beam source apparatus is described which creates a plasma with two distinct density regions separated by a transition which is shorter than the plasma skin depth kp^−1 of either region. This sharp density modulation is achieved by using a perforated stainless steel screen to filter half of a diffusing plasma column. A simple physical model predicts that the length of the plasma density transition will vary with the distance from the screen. For a weakly magnetized plasma, the transition length will be twice the distance, on a line normal to the screen plane, from the screen edge to the location where the transition is measured. The plasma column is generated using an argon discharge plasma source. It has a peak density of approximately 3.53 X 10^13 cm^−3 and a full width half maximum width of 5 cm. The discharge source utilizes a 7.5 cm diameter LaB6 disk cathode heated to 1300 °C using a graphite heater. The plasma column is filtered with a 78 mm thick stainless steel sheet with 152 mm holes and 21% open area. Plasma density transitions with lengths between 0.74 and 0.95 kp^−1 were measured. |
| title: | Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators |
| journal: | Physical Review Letters |
| vol-pages: | 95:195002 |
| year: | 2005 |
| authors: | J. Rosenzweig,A. Cook,A. Scott,M. Thompson,R. Yoder |
| abstract: | Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear have included intense electron beams with densities many times in excess of the plasma beam’s electric fields expel the plasma electrons from the beam path to many beam radii in We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are Implications of ion motion on the feasibility of the PWFA-based colliders are discussed. |
| title: | Emittance compensation with dynamically optimized photoelectron beam profiles |
| journal: | Nuclear Instruments and Methods in Physics Research A |
| vol-pages: | 57:87 |
| year: | 2005 |
| authors: | J. Rosenzweig,A. Cook,M. Dunning,M. Ferrario |
| abstract: | Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam’s longitudinal extrema. These nonlinearities are known to produce both transverse and longitudinal emittance growth. On the other hand, it has recently been shown by Luiten that by illuminating the cathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most recent photoinjectors. It is seen that the two processes are compatible, with simulations indicating a very high brightness beam can be obtained. The robustness of this scheme to systematic errors is examined. Prospects for experimental tests of this scheme are discussed. |
| title: | Experimental and Analytical Study of a High Gain Self Amplified Spontaneous Emission Free Electron Laser Operating in a Large Spectral Bandwidth Regime |
| format: | thesis |
| year: | 2005 |
| authors: | Gerard Andonian |
| abstract: | The drive to create and measure ultra-short pulses in the x-ray regime advances the ongoing development of free electron lasers (FEL). Several proposed schemes, to shorten the pulse length of the radiation, involve driving the FEL with a chirped (linear longitudinal phase space correlation) electron beam in the self amplified spontaneous emission (SASE) mode. This dissertation examines the experiments conducted under such conditions, canvassing analytical and numerical studies of beam dynamics and radiation properties, experimental observations, and descriptions of the development of novel diagnostics. The VISA (Visible-Infrared SASE Amplifier) program has achieved saturation at 840 nm within a 4 m long undulator. A novel bunch compression mechanism during transport was discovered and ultimately responsible for the high peak current required to drive the FEL. Start-to-end simulations, detailing the dynamics from electron beam inception at the photocathode to the FEL radiation properties at the undulator, were successfully benchmarked to observable data. |
| title: | High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| authors: | P. Musumeci,S. Tochitsky,S. Boucher,C. Clayton,A. Doyuran,R. England,C. Joshi,C. Pellegrini,J. Ralph,J. Rosenzweig,C. Sung,S. Tolmachev,G. Travish,A. Varfolomeev,A. Jr.,T. Yarovoi,R. Yoder |
| abstract: | Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an Inverse-Free- Electron-Laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and Żeld amplitude. The Rayleigh range of the laser, » 1.8 cm, is much shorter than the undulator length yielding a di®raction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the Żrst half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator. |
| title: | Higher harmonic inverse free-electron laser interaction |
| journal: | Physical Review E |
| vol-pages: | |
| year: | 2005 |
| authors: | P. Musumeci,C. Pellegrini,J. Rosenzweig |
| abstract: | We expand the theory of the inverse free electron laser IFEL interaction to include the possibility of energy exchange that takes place when relativistic particles traversing an undulator interact with an electromagnetic wave of a frequency that is a harmonic of the fundamental wiggler resonant frequency. We derive the coupling coefficients as a function of the IFEL parameters for all harmonics, both odd and even. The theory is supported by simulation results obtained with a three-dimensional Lorentz equation solver code. Comparisons are made between the results of theory and simulations, and the recent UCLA IFEL experimental results where higher harmonic IFEL interaction was observed. |
| title: | Neptune Second Harmonic Generation Autocorrelator |
| format: | tech note |
| year: | 2005 |
| authors: | R. England |
| abstract: | This document provides detailed information on the basic theoretical knowledge required to understand the operational principles of the Second Harmonic Generation Autocorrelator used for measuring the pulse length of the infrared drive laser at the Neptune Laboratory. This autocorrelator was originally assembled by Kari Sanders and Sergei Tochitsky ca. 2000-2001. Some information about its operation may be found in Kari Sanders' master's thesis. In short, the autocorrelator operates by splitting the infrared (1064nm) pulse produced by the Neptune regenerative amplifier and grating compressor and then crossing the two split pulses inside of a nonlinear KDP crystal, via a Type I "ooe" interaction, to produce noncollinear second harmonic frequency upconversion to green (532 nm). The intensity of the green as a function of the delay between the two split pulses produces the autocorrelation of the pulse, which can be used to extract the pulse length and (to some extent) the time structure of the pulse. The theory of autocorrelation will not be discussed in this document. |
| title: | New Features in UCLA-PARMELA v 2.1 |
| format: | tech note |
| year: | 2005 |
| authors: | R. England |
| abstract: | This document describes modifications to the UCLA-PARMELA source code version 2.0. The modifications were made by R. J. England during the period from 2003 to 2005. The changes to the code consist of: (1) the implementation of the "SEXT" card for sextupoles, and (2) changes to the "TRWAVE" card which permit the fields to be printed out to a data file. These changes are detailed in the following subsections. In addition, (3) I document the input structure for the CELL card in versions 2.0 and 2.1 since this was found to differ from the description given in the UCLA-PARMELA manual. The modified code version number has been increased to v 2.1. |
| title: | Observation of Anomalously Large Spectral Bandwidth in a High Gain Self-amplified Spontaneous Emission Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| authors: | G. Andonian,A. Murokh,J. Rosenzweig,R. Agustsson,M. Babzien,I. Ben-Zvi,P. Frigola,J. Huang,L. Palumbo,C. Pellegrini,S. Reiche,G. Travish,C. Vicario,V. Yakimenko |
| abstract: | Observation of ultra-wide bandwidth, up to a full width of 15%, high-gain operation of a self-amplified spontaneous emission free election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (~ 1.7%) emitted from the accelerator. Because of non-linear pulse compression during beam transport, a short, high current pulse with strong mismatch errors is injected into the undulator, bringing about high FEL gain. Start-end simulations reproduce key features of the measured results, and provide insight into mechanisms, such as angular spread in both emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum. |
| title: | Observation of Anomalously Large Spectral Bandwidth in a High-Gain Self-Amplified Spontaneous Emission Free Elctron Laser |
| journal: | Physical Review Letters |
| vol-pages: | 95:054801 |
| year: | 2005 |
| authors: | G. Andonian,A. Murokh,J. Rosenzweig,R. Agustsson,M. Babzien,I. Ben-Zvi,P. Frigola,J.Y Huang,L. Palumbo,C. Pellegrini,S. Reiche,G. Travish,C. Vicario,V. Yakimenko |
| abstract: | Observation of ultrawide bandwidth, up to 15% full-width, high-gain operation of a self-amplified spontaneous emission free-election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (E=E 1:7%) emitted from the accelerator. Because of nonlinear pulse compression during transport, a short, high current bunch with strong mismatch errors is injected into the undulator, giving high FEL gain. Start-to-end simulations reproduce key features of the measurements and provide insight into mechanisms, such as angular spread in emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum. |
| title: | PRELIMINARY RESULTS FROM THE UCLA/SLAC ULTRA-HIGH GRADIENT CERENKOV WAKEFIELD ACCELERATOR EXPERIMENT |
| conference: | Erice 2005 |
| year: | 2005 |
| authors: | M. THOMPSON,H. BADAKOV,J. ROSENZWEIG,G. TRAVISH,M. HOGAN,R. ISCHEBECK,N. KIRBY,P. MUGGLI,A. SCOTT,R. YODER |
| abstract: | The first phase of an experiment to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range has been completed. This experiment takes advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., ?z = 20 ?m at Q = 3 nC). The FFTB electron beam has been successfully focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 ?m / OD = 325 ?m and ID = 100 ?m / OD = 325 ?m. The pulse length of the electron beam was varied in the range 20 ?m < ?z < 100 ?m which produced a range of electric fields between 2 and 20 GV/m at the inner surface of the dielectric tubes. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the surfaced fields that were sustained equate to on axis accelerating field of several GV/m. In future experiments we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain more information about the strength of the accelerating fields. |
| title: | Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| authors: | J. Lim,A. Doyuran,P. Frigola,G. Travish,J. Rosenzweig,S. Anderson,S. Betts,J. Crane,D. Gibson,F. Hartemann,A. Tremaine |
| abstract: | We describe an experiment for production of high harmonic x-ray radiation from Thomson backscattering of an ultra-short high power density laser by a relativistic electron beam at the PLEIADES facility at LLNL. In this scenario, electrons execute a ``figure-8'' motion under the influence of the high-intensity laser field, where the constant characterizing the field strength is expected to exceed unity: $a_{L}=eE_{L}/m_{e}c\omega_{L}\geq1$. With large $a_{L}$ this motion produces high harmonic x-ray radiation and significant broadening of the spectral peaks. This paper is intended to give a layout of the PLEIADES experiment, along with progress towards experimental goals. |
| title: | Proposed continuous wave energy recovery operation of an x-ray free electron laser |
| journal: | Physical Review Special Topics - Accelerators and Beams |
| vol-pages: | 8: 010701 |
| year: | 2005 |
| authors: | J. Sekutowicz,S. Bogacz,D. Douglas,P. Kneisel,G. Williams,M. Ferrario,I. Ben-Zvi,J. Rose,J. Smedley,T. Srinivasan-Rao,L. Serafini,W.-D Moller,B. Petersen,D. Proch,S. Simrock,P. Colestock,J. Rosenzweig |
| abstract: | Commissioning of two large coherent light facilities (XFELs) at SLAC and DESY should begin in 2008 and 2011, respectively. In this paper we look further into the future, hoping to answer, in a very preliminary way, two questions. First: What will the next generation of XFEL facilities look like? Believing that superconducting technology offers advantages such as high quality beams with highly populated bunches, the possibility of energy recovery and higher overall efficiency than warm technology, we focus this preliminary study on the superconducting option. From this belief the second question arises: What modifications in superconducting technology and in the machine design are needed, as compared to the present DESY XFEL, and what kind of research and development program should be proposed to arrive in the next few years at a technically feasible solution with even higher brilliance and increased overall conversion of ac power to photon beam power? In this paper we will very often refer to and profit from the DESY XFEL design, acknowledging its many technically innovative solutions. |
| title: | Pulsed-laser nonlinear Thomson scattering for general scattering geometries |
| journal: | Physical Review E |
| vol-pages: | 72:056502 |
| year: | 2005 |
| authors: | G. Krafft,A. Doyuran,J. Rosenzweig |
| abstract: | In a recent paper it has been shown that single electron Thomson backscatter calculations can be performed including the effects of pulsed high intensity lasers. In this paper we present a more detailed treatment of the problem and present results for more general scattering geometries. In particular, we present new results for 90° Thomson scattering. Such geometries have been increasingly studied as x-ray sources of short-pulse radiation. Also, we present a clearer physical basis for these different cases. |
| title: | RF AND MAGNETIC MEASUREMENTS ON THE SPARC PHOTOINJECTOR AND SOLENOID AT UCLA |
| conference: | PAC 2005 |
| year: | 2005 |
| authors: | J.B Rosenzweig,A.M Cook,M.P Dunning,P. Frigola,G. Travish,C. Sanelli,F. Tazzioli,D.T Palmer |
| abstract: | The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made. |
| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| format: | preprint |
| year: | 2005 |
| authors: | G. Andonian,R. Agustsson,P. Frigola,A. Murokh,C. Pellegrini,S.Reiche S.Reiche,J. Rosenzweig,G. Travish,M. Babzien,I. Ben-Zvi,V. Litvinenko,V. Yakimenko,I. Boscolo,S. Cialdi,A. Flacco,M. Ferrario,L. Palumbo,C. Vicario,J. Huang |
| abstract: | The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating)technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported. |
| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| authors: | G. Andonian,R. Agustsson,P. Frigola,A. Murokh,C. Pellegrini,S.Reiche S.Reiche,J. Rosenzweig,G. Travish,M. Babzien,I. Ben-Zvi,V. Litvinenko,V. Yakimenko,I. Boscolo,S. Cialdi,A. Flacco,M. Ferrario,L. Palumbo,C. Vicario,J. Huang |
| abstract: | The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating) technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported. |
| title: | Side-Coupled Slab-Symmetric Structure for High-Gradient Acceleration using Terahertz Power |
| format: | preprint |
| year: | 2005 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: |
| title: | Side-coupled slab-symmetric structure for high-gradient acceleration using terahertz power |
| journal: | Physical Review Special Topics - Accelerators and Beams |
| vol-pages: | 8:111301 |
| year: | 2005 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: | A slab-symmetric dielectric-loaded accelerator structure, consisting of a vacuum gap between dielectric-lined conducting walls, is described. The device is resonantly excited by an external drive laser which is side coupled into the acceleration region; a novel coupling scheme, which consists of an array of narrow, equally spaced slots in the upper structure boundary, is presented and analyzed in detail. This structure partakes of the advantages of earlier slab-symmetric optical acceleration proposals, but will use a terahertz-frequency external radiation source ( 340 m), allowing realistic electron beams to be used in a proof-of-principle experiment. Two- and three-dimensional electromagnetic simulations are used to verify the mode patterns and study the effects of the couplers, including time-dependent calculations of the filling of the structure and particle-in-cell computations of the beam wakefields. Details of the resonance are found to be highly sensitive to the coupling slot geometry: the presence of the couplers can lead to frequency detuning, changes in the field breakdown limits and overall Q factor, and distortions of the field pattern. Beam wakefields are enhanced by the presence of the slots, but found to have no significant effect on the beam transport. The resonant accelerating fields, which are nearly constant along the short transverse direction, are found to have between 10 and 15 times the amplitude of the driving radiation, with only a small ( < 10%) admixture of other nonaccelerating modes. Field gradients are computed to be near 100 MV=m when the structure is driven with 100MWof terahertz laser power. Possible manufacturing methods for a prototype device are discussed. |
| title: | Successful beam-beam tuneshift compensation |
| format: | thesis |
| year: | 2005 |
| authors: | Kip Bishofberger |
| abstract: | The performance of synchrotron colliders has been limited by the beam-beam limit, a maximum tuneshift that colliding bunches could sustain. Due to bunch-to-bunch tune variation and intra-bunch tune spread, larger tuneshifts produce severe emittance growth. Breaking through this constraint has been viewed as impossible for several decades. A device known as the Tevatron Electron Lens (TEL) has been designed, constructed, and tested in the Tevatron at Fermilab. This device produces a pulsed beam of electrons which interact with the antiproton bunches in the Tevatron. The peak beam current is typically 2 A, and the beam energy can range from 4 keV to 12 keV. The bunches interact with the beam’s electromagnetic field, causing their tunes to shift opposite to the beam-beam limit. By tailoring the electron-beam current for each bunch, the tuneshift can be individualized to compensate for the adverse bunch-to-bunch variation. Additionally, shaping the electron-beam profile shifts the tune of each antiproton within each bunch selectively depending on their amplitude, compensating for the intra-bunch tune spread. The typical tuneshift that each antiproton feels is 0.0097 per interaction point, and the bunch-to-bunch tune variation is approximately 0.007. The tune spread within each bunch is expected to be about 0.004. Experiments with the TEL yielded tuneshifts with proton bunches equal to 0.0089, which is equivalent to antiproton tuneshifts of 0.0112. This value is more than necessary to successfully compensate the beam-beam interactions. Additionally, the use of the TEL has significantly reduced antiproton losses and emittance growth, evidence that such compensation is indeed beneficial to synchrotron operation. This dissertation introduces the physics of ultra-relativistic synchrotrons and low-energy electron beams, with emphasis placed on the limits of the Tevatron and the needs of a tuneshift-compensation device. A detailed analysis of the TEL is given, comparing theoretical models to experimental data whenever possible. Finally, results of Tevatron operations with inclusion of the TEL are presented and analyzed. It is shown that the TEL provides a way to shatter the previously inescapable beam-beam limit. |
| title: | Transverse phase space coupling due to quadrupole errors in the SPARC photoinjector |
| format: | talk |
| year: | 2005 |
| authors: | J.B Rosenzweig |
| abstract: |
| title: | Traveling wave undulators for FELs and synchrotron radiation sources. |
| format: | preprint |
| year: | 2005 |
| authors: | C. Pellegrini |
| abstract: | We study the use of a traveling wave waveguide as an undulator for short wavelength free-electron lasers (FELs) and synchrotron radiation sources. This type of undulator -which we will call TWU- can be useful when a short electron oscillation period and a large aperture for the propagation of the beam are needed. The availability of high power X-band microwave sources, developed for the electron-positron linear collider, make it possible today to build TWUs of practical interest to produce short wavelength radiation from a beam of reduced energy respect to the case of more conventional undulators. In this paper we will discuss the characteristic of the TWU, the systems that can be used to control the effect of RF power losses in the waveguide walls, and how to optimize a TWU and the associated electron transport system for use in a synchrotron radiation source or FEL. |
| title: | UCLA Neptune CTR Interferometer |
| format: | tech note |
| year published: | 2005 |
| year authored: | 2003 |
| authors: | R. England |
| abstract: | The purpose of this document is to outline the basic operating theory behind the coherent transition radiation (CTR) interferometry technique employed at the UCLA Neptune Laboratory for diagnosing the bunch length of the electron beam produced by the Neptune 1.6-cell gun and PWT accelerating structure. General theoretical results are presented and then applied specifically to the Neptune interferometer developed by Uwe Happek, which we refer to henceforth as the Uwefarometer. Particular attention is paid to understanding the theory of the wire-grid polarizers which are used in the Uwefarometer to split and recombine the terahertz CTR radiation. |
| title: | Velocity bunching of high-brightness electron beams |
| journal: | Physical Review Special Topics - Accelerators and Beams |
| vol-pages: | 8:014401 |
| year: | 2005 |
| authors: | S. Anderson,P. Musumeci,J. Rosenzweig,W. Brown,R. England,M. Ferrario,J. Jacob,M. Thompson,G. Travish,A. Tremaine,R. Yoder |
| abstract: | Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modernhigh brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented. |
| title: | Working Group 2 Summary: Diagnostics and Beam Manipulation |
| format: | talk |
| year: | 2005 |
| authors: | G. Travish |
| abstract: | A summary presentation of working group 2 of the ICFA Workshop of High Brightness Beams. The working group included talks on beam diagnostics and beam manipulation. |
| title: | X-Band Dipole Mode Deflecting Cavity for the UCLA Neptune Beamline |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| authors: | R. England,B. O'Shea,J. Rosenzweig,G. Travish,and Alesini |
| abstract: | We report progress on the design and construction of a nine-cell cavity operating in a TM110-like dipole mode for use as a temporal diagnostic of the 14 MeV, 300 pC electron bunches generated at the UCLA Neptune Laboratory linear accelerator, with an anticipated temporal resolution of 50 fs at a peak input power of 50 kW. The cavity is a center-fed standing-wave pi-mode structure, operating at 9.6 GHz, and incorporating a knife-edge and gasket assembly which minimizes the need for brazing or welding. Results of initial RF testing of the prototype cavity are discussed and compared with simulation results obtained using the commercial code HFSS. |
| title: | A Helical Undulator Wave-guide Inverse Free-Electron Laser |
| conference: | |
| year: | 2004 |
| authors: | J. Rosenzweig,N. Bodzin,P. Frigola,C. Joshi,P. Musumeci,C. Pellegrini,S. Tochitsky,and Travish |
| abstract: | With recent success in high gradient, high-energy gain IFEL experiments at the UCLA Neptune Laboratory, future experiments are now being contemplated. The Neptune IFEL was designed to use a tightly focused, highly diffracting, near-TW peak power 10 micron laser. This choice of laser focusing, driven by power-handling limitations of the optics near the interaction region, led to design and use of a very complex undulator, and to sensitivity to both laser misalignment and focusing errors. As these effects limited the performance of the IFEL experiment, a next generation experiment at Neptune has been studied which avoids the use of a highly diffractive laser beam through use of a waveguide. We discuss here the choice of low-loss waveguide, guided mode characteristics and likely power limitations. We also examine a preferred undulator design, which is chosen to be helical in order to maximize the acceleration achieved for a given power. With the limitations of these laser and undulator choices in mind, we show the expected performance of the IFEL using 1D simulations. Three-dimensional effects are examined, in the context of use of a solenoid for focusing and acceleration enhancement. |
| title: | A PMQ-based, Ultra-short Focal Length, Final Focus System for Next Generation Beam-Radiation and Beam-Plasma Experiments |
| format: | talk |
| year: | 2004 |
| authors: | G. Travish |
| abstract: | Next-generation advanced-accelerators such as the PWFA, and beam-radiation interactions such as inverse-Compton scattering, depend on increased beam-density to achieve superior results. The photoinjector has enabled the production of high-brightness beams that are desirable for experiments with critical dependencies on bunch length and emittance. Along with the production of shorter and lower-emittance beams, comes the need to produce shorter focal-lengths (beta-functions). An approach to creating strong focusing-channels using high field, small-bore permanent-magnet quadrupoles (PMQs) has been followed by the authors. A focusing system using three PMQs, each composed of 16 Nd-Fe-B sectors in a Halbach geometry has been installed in the PLEIADES inverse-Compton experiment. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis. This presentation covers the details of the focusing system, experimental experience, and implications for future experiments with an emphasis on advanced accelerators. |
| title: | A PMQ-based, Ultra-short Focal Length, Final Focus System for Next Generation Beam-Radiation and Beam-Plasma Experiments |
| conference: | |
| year: | 2004 |
| authors: | G. Travish,P. Frigola,J. Lim,J. Rosenzweig |
| abstract: | Abstract. Next-generation advanced-accelerators such as the PWFA, and beam-radiation interactions such as inverse-Compton scattering, depend on increased beam-density to achieve superior results. The photoinjector has enabled the production of high-brightness beams that are desirable for experiments with critical dependencies on bunch length and emittance. Along with the production of shorter and lower-emittance beams, comes the need to produce shorter focal-lengths (beta-functions). An approach to creating strong focusing-channels using high field, small-bore permanent-magnet quadrupoles (PMQs) has been followed by the authors. A focusing system using three PMQs, each composed of 16 Nd-Fe-B sectors in a Halbach geometry has been installed in the PLEIADES inverse-Compton experiment. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis. This paper covers the details of the focusing system, experimental experience, and implications for future experiments with an emphasis on advanced accelerators. |
| title: | An Optimal Design for a THz Dielectric-Loaded Slab-Symmetric Accelerator |
| conference: | |
| year: | 2004 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: | A slab-symmetric dielectric-loaded accelerator structure, consisting of a vacuum gap between dielectric-lined conducting walls, is analyzed theoretically and computationally. The device is to be resonantly excited by an external laser source of wavelength 340 µm. Analytical results for infinite and finite-width geometries are summarized, and 2D electromagnetic simulation is used to demonstrate the time-dependent filling of the structure from the external source. The resonant accelerating fields, which are nearly constant along the short transverse direction, are found to have between 10 and 15 times the amplitude of the driving radiation, with only a small (< 10%) admixture of other non-accelerating modes. Field gradients are near 100 MV/m when the structure is driven with 100 MW of terahertz power. The resonance is highly dependent on the geometry of the slots used to couple radiation into the structure, with effects on the overall Q-factor, frequency detuning, and field pattern. Possible manufacturing methods are discussed, along with an all-dielectric version of the design that would allow scaling of the structure to a wavelength of 10 µm. |
| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| conference: | |
| year: | 2004 |
| authors: | J.B.Rosenzweig J.B.Rosenzweig,S. Hoover,M.J Hogan,P. Muggli,M. Thompson,G. Travish,R. Yoder |
| abstract: | The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, ! "z= 20 µm) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields. |
| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| conference: | |
| year: | 2004 |
| authors: | J.B Rosenzweig,S. Hoover,M.J Hogan,P. Muggli,M. Thompson,G. Travish,R. Yoder |
| abstract: | The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, ) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields. |
| title: | Calculation of Coherent Radiation from Ultra-short Electron Beams Using a Liénard-Wiechert Based Simulation Code |
| format: | |
| year: | 2004 |
| authors: | A. Flacco,M. Fairchild,S. Reiche,J.B Rosenzweig,L. Giannessi,M. Quattromini |
| abstract: | The coherent radiation emitted by electrons in high brightness beam-based experiments is important from the viewpoints of both radiation source development, and the understanding and diagnosing the basic physical processes important in beam manipulations at high intensity. While much theoretical work has been developed to aid in calculating aspects of this class of radiation, these methods do not often produce accurate information concerning the experimentally relevant aspects of the radiation. At UCLA, we are particularly interested in coherent synchrotron radiation and the related phenomena of coherent edge radiation, in the context of a fs-beam chicane compression experiment at the BNL ATF. To analyze this and related problems,we have developed aprogramthat acts as an extension to the Liénard-Wiechert-based 3D simulation code TREDI, termed FieldEye. This program allows the evaluation of electromagnetic fields in the time and frequency domain in an arbitrary 2D detector planar area.We discuss here the implementation of the FieldEye code, and give examples of results relevant to the case of the ATF chicane compressor experiment. |
| title: | Considerations for Conical Horn Antenna Design optimizing Cerenkov radiation from hollow cylindrical dielectric tube |
| format: | tech note |
| year: | 2004 |
| authors: | Hristo Badakov |
| abstract: |
| title: | Creation of plasma density transitions short compared to the plasma skin depth |
| format: | preprint |
| year: | 2004 |
| authors: | M. Thompson,J. Rosenzweig,G. Travish |
| abstract: | A plasma based electron beam source apparatus is described which creates a plasma with two distinct density regions separated by a transition which is shorter than the plasma skin depth $k^{-1}_{p}$ of either region. This sharp density modulation is achieved by using a perforated stainless steel screen to filter half of a diffusing plasma column. A simple physical model predicts that the length of the plasma density transition will vary with the distance from the screen. For a weakly magnetized plasma, the transition length will be twice the distance, on a line normal to the screen plane, from the screen edge to the location where the transition is measured. The plasma column is generated using an argon discharge plasma source. It has a peak density of approximately 3.5 x 10$^{13}$ cm$^{-3}$ and a FWHM width of 5 cm. The discharge source utilizes a 7.5 cm diameter LaB$_{6}$ disc cathode heated to $1300^{\circ}$ C using a graphite heater. The plasma column is filtered with a 78 $\mu$m thick stainless steel sheet with 152 $\mu$m holes and 21\% open area. Plasma density transitions with lengths between 0.74$k^{-1}_{p}$ and 0.95$k^{-1}_{p}$ were measured. |
| title: | Design, Construction, Simulation and Implementation of a Magnetic Electron Bunch Compressor |
| format: | thesis |
| year: | 2004 |
| authors: | Ronald Agustsson |
| abstract: | Throughout the last half century, electron beam brightness has been the quantitative benchmark for measuring the advancement of light sources. The generation of these high brightness beams often require compaction techniques to decrease the longitudinal extent of the beam, consequently increasing the current. Presently, one of the popular methods for obtaining the amplification of current in electron beams is by magnetic compression. Magnetic bunch compression is a fairly common tool utilized by the accelerator community, however it can still be considered a stand alone instrument since the details of the physics that affect this type of electron beam manipulation are not categorically well understood. Of particular interest is the coupling between the longitudinal and transverse phase space planes and the forces responsible for the effects that contribute to the dilution of the transverse emittance in the bend plane of the beam. This thesis details the design, construction, simulation, testing and implementation of a magnetic bunch compressor at the Accelerator Test Facility (ATF), a leading photoinjector users' facility located within the Brookhaven National Laboratory (BNL). Simulations show that the magnetic chicane bunch compressor increases the peak current of the ATF electron beam by a significant factor while only sustaining a nominal increase in the bend plane emittance. Additionally, some interesting effects from the inclusion of coherent synchrotron radiation in the simulations such as linearization of the lower energy portion of the beam and smearing of the longitudinal distribution are demonstrated. |
| title: | Development of X-ray Free-electron Lasers |
| journal: | IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, |
| vol-pages: | VOL. 10, NO. 6, p. 1393-1404 |
| year: | 2004 |
| authors: | C. Pellegrini,S. Reiche |
| abstract: | We review and discuss the theoretical and experimental work that has led to the development of short wavelength free-electron lasers operating as single pass amplifiers, starting from the spontaneous undulator radiation, in the self amplified spontaneous emission mode. This work has led to several projects to build this type of free-electron lasers operating at a wavelength of about 0.1 nm, producing coherent X-ray pulses with an unprecedented brilliance and peak power, and pulse length in the femtosecond range. One such project, the LCLS, is presently under construction and is expected to be operational in 2008. |
| title: | Enhanced Acceleration of Injected Electrons in a Laser Beatwave Induced Plasma Channel |
| format: | preprint |
| year: | 2004 |
| authors: | S. Tochitsky,R. Narang,C. Filip,P. Musumeci,C. Clayton,R. Yoder,K. Marsh,J. Rosenzweig,C. Pellegrini,and Joshi |
| abstract: | Enhanced energy gain of externally injected electrons by a ~3-cm long, high-gradient relativistic plasma wave (RPW) is demonstrated. Using a CO2 laser-beatwave of duration longer than the ion motion time across the laser spot size, a laser self-guiding process is initiated in a plasma channel. Guiding compensates for ionization-induced defocusing (IID) creating a longer plasma, which extends the interaction length between electrons and the RPW. In contrast to a maximum energy gain of 10 MeV when IID is dominant, the electrons gain up to 38 MeV energy in a laser beatwave induced plasma channel. PACS: 52.35Mw, 52.38Hb, 52.38Kd |
| title: | Free-Electron Lasers as Pumps for High-Energy Solid-State Lasers |
| conference: | 25th International Free Electron Laser Conference |
| year published: | 2004 |
| year authored: | 2003 |
| authors: | G. Travish,J. Crane,A. Tremaine |
| abstract: | High average-power free-electron lasers may be useful for pumping high peak-power solid-state laser-amplifiers. At very high peak-powers, the pump source for solid-state lasers is non-trivial: flash lamps produce thermal problems and are unsuitable for materials with short florescence-times, while diodes can be expensive and are only available at select wavelengths. FELs can provide pulse trains of light tuned to a laser material's absorption peak, and florescence lifetime. An FEL pump can thus minimize thermal effects anad potentially allow for new laser materials to be used. This paper examines the design of a high average-power, effecient high-gain FEL for use as a pump source. Specifically, the cases of a 100 J class pump, and a 100 TW-class laser at a planned fourth-generation light-source are considered. |
| title: | Plasma Density Transition Trapping of Electrons in Plasma Wakefield Accelerators |
| format: | thesis |
| year: | 2004 |
| authors: | Matthew Thompson |
| abstract: | Plasma based electron beam sources, which are now under development, will produce beams with much higher particle densities than are currently available. Plasma sources can create beams with brightness (the measure of achievable beam density) orders of magnitude greater than radio frequency photoinjectors, the current state-of-the-art. Plasma density transition trapping is one example of the many plasma electron beam source schemes under development. Plasma density transition trapping is a recently proposed self-injection mechanism for plasma wake field accelerators. The technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake field. This dissertation examines the different regimes in which plasma density transition trapping can operate and the quality of the electron beams captured in terms of emittance, energy spread, and brightness. This is accomplished using two-dimensional Particle-In-Cell (PIC) simulations which show that the captured beam parameters can be optimized by manipulating the overall plasma density, as well as the density profile. A general set of scaling laws is developed that predicts how the brightness of transition trapping beams, or the beams produced by any plasma system, scales with the plasma density. These scaling laws predict that beam brightness increases linearly with the plasma density of the source. The design and execution of the first plasma density transition trapping experiment is also documented in this dissertation. Plasma with density on the order of 10E-13 / cm^-3 was used in the experiment. Plasma density transitions steep enough to produce trapping at this density were created and measured. Interaction between the plasma transition and a driving electron beam pulse did not, however, produce trapped electrons. Detailed measurements of the drive beam parameters revealed that it did not meet the trapping experiment design criteria. Simulations using the measured plasma and beam parameters predict zero captured charge in agreement with observations. |
| title: | Plasma density transition trapping as a possible high-brightness electron beam source |
| journal: | PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS |
| vol-pages: | 7:011301 |
| year: | 2004 |
| authors: | M.C Thompson,J.B Rosenzweig,H. Suk |
| abstract: | Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile.We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness > 5 x 10^14 A/(mrad)^2. A proof-ofprinciple transition trapping experiment is planned for the near future. The proposed experiment is described in detail. |
| title: | Procedure for the production of a 10 micron aluminum foil OTR window |
| format: | tech note |
| year: | 2004 |
| authors: | M. Thompson |
| abstract: |
| title: | Status of the UCLA/NICADD Plasma Density Transition Trapping Experiment |
| format: | preprint |
| year: | 2004 |
| authors: | M.C Thompson,J.B Rosenzweig,G. Travish,N. Barov,H. Edwards,P. Piot,J. Santucci,R. Tikhoplav |
| abstract: | Plasma density transition trapping is a recently proposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. This paper recounts the first attempt to demonstrate density transition trapping experimentally. The goal of the experiment is to capture a ∼ 100 pC, 1.5 MeV beam with 4% rms energy spread out of a 2.5x10^13 cm^−3 peak density plasma using a 6nC, 14 MeV drive beam. The first experimental run occurred at the Fermilab NICADD Photoinjector Laboratory (FNPL) between January and May 2004. While several key objectives were achieved, we were unable to achieve the drive beam parameters necessary for the experiment due to technical problems. We are in the process of resolving these problems in preparation for a second experimental run. |
| title: | The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators |
| conference: | |
| year: | 2004 |
| authors: | J.B Rosenzweig,A.M Cook,M.C Thompson,R. Yoder |
| abstract: | Recent proposals for using plasma wakefield accelerators in the blowout regime as a component of a linear collider have included very intense driver and accelerating beams, which have densities many times in excess of the ambient plasma density. The electric fields of these beams are widely known to be large enough to completely expel plasma electrons from the beam path; the expelled electrons often attain relativistic velocities in the process. We examine here another aspect of this high-beam density scenario: the motion of ions. In the lowest order analysis, for both cylindrically symmetric and “flat” beams, it is seen that for the “after-burner” scenario discussed at AAC 2004 the ions completely collapse inside of the electron beam. In this case the ion density is significantly increased, with a large increase in the beam emittance expected as a result. We also examine a less severe scenario, where the ion collapse onset is expected, and new, coupled equilibria in the beam and plasma density are created. |
| title: | A Fast Method to Estimate the Gain of the Microbunch Instability in a Bunch Compressor |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | S. Reiche,J. Rosenzweig |
| abstract: | For the users of the high-brightness radiation sources of free-electron lasers it is necessary to reduce the FEL pulse length to 10 fs and below for time-resolving pump and probe experiments. Although it can be achieved by conventional compression methods for the electron beam or the chirped FEL pulse, the technical realization is demanding. In this presentation we study the impact of undulator wakefields and how their properties can be used to reduced the amplifying part of the bunch to the desired length. Methods of actively controlling the wakefields are presented. |
| title: | A Plasma-Assisted High-Brightness X-Ray Source via Inverse Compton Scattering |
| format: | unpublished |
| year: | 2003 |
| authors: | J. Rosenzweig,R. Yoder,G. Travish |
| abstract: |
| title: | A Resonant, THz Slab-Symmetric Dielectric-Based Accelerator |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: | Slab-symmetric dielectric-loaded structures, consisting of a vacuum gap between dielectric-lined conducting walls, have become a subject of interest for highgradient acceleration of high-charge beams due to their simplicity, relatively low power density, and advantageous beam dynamics. Such a structure can be resonantly excited by an external power source and is known to strongly suppress transverse wakefields. Motivated by the prospect of a high-power FIR radiation source, currently under construction at UCLA, we investigate a high-gradient slabsymmetric accelerator powered by up to 100 MW of laser power at 340 ?m, with a predicted gradient near 100 MeV/m. Theory and simulation studies of the structure fields and wakes are presented, with an outline of a future experiment. |
| title: | A Slab-Symmetric Dielectric-Loaded Structure for High-Gradient Acceleration at THz |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: | We present a design for a slab-symmetric accelerating structure to be resonantly excited at terahertz frequencies. The device, consisting of a vacuum gap between dielectric-lined walls, combines the advantages of a slab geometry (including strong suppression of transverse beam wakefields and low power density) with the existence of a resonant mode having phase synchronism with relativistic electrons. Accelerating fields of hundreds of MeV/m are predicted when the structure is powered by a high-power FIR radiation source in development at UCLA. Simulation of the structure fields is described and compared with theory, and an experimental program is discussed. |
| title: | A fast method to estimate the gain of the microbunch instability in a bunch compressor |
| conference: | 24th International Free Electron Laser Conference |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | S. Reiche,J. Rosenzweig |
| abstract: | To reach high peak currents driving Free-Electron Lasers an initial chirped electron bunch is compressed in a bunch compressor. The interaction of the electron beam with its radiation field can yield a collective instability, which amplifies any initial modulation in the current profile. We present a model, which allows to derive an explicit analytical expression for the gain of the microbunch instability. The results are compared to those of the more complex analytical models. |
| title: | Acceleration of Injected Electrons In A Laser Beatwave Experiment |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | S. Tochitsky,R. Narang,C. Filip,P. Musumeci,C. Clayton,R. Yoder,K. Marsh,J. Rosenzweig,C. Pellegrini,C. Joshi |
| abstract: | Plasma-based accelerators of particles are of great interest because plasmas can sustain very strong electric fields. They are utilizing a relativistic plasma wave with a phase velocity close to the speed of light driven by a high-power laser beam. The Neptune Laboratory at UCLA is being used for plasma beatwave acceleration of injected electrons. Here, a two-wavelength laser pulse (frequencies w1,w2) resonantly drives a longitudinal electron plasma wave of frequency equal to w1-w2, providing a field strength of GeV/m and, therefore, accelerates an injected electron beam at this very high gradient. A 10 ps beam of 12 MeV electrons is loaded in a 3-cm long plasma beatwave accelerator driven by a TW CO2 laser pulse. At the resonance condition, the electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that for large volume diffraction limited plasmas, when efficiency of the plasma wave excitation is restricted by ionization-induced refraction, acceleration of electrons is enhanced significantly by using asymmetric (fast front and slow fall) long pulses. 2D PIC simulations revealed that guiding of the laser pulse in a ponderomotive, self-induced ion channel, formed ~200 ps after the field ionization, allows compensation for the ionization-induced defocusing and efficient driving of the beatwave over the entire length. |
| title: | An Adjustable Permanent Magnet Quadrupole Final Focus System for Low Energy Experiments |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | J. Lim,P. Frigola,J. Rosenzweig,S. Telfer,G. Travish,W. Brown,A. Tremaine |
| abstract: | The final focus system for the Thomson X-ray scattering experiment termed PLEIADES (Picosecond Laser-Electron InterAction for Dynamic Evaluation of Structures) at LLNL demands ultra-high field gradient quadrupoles in order to focus initially small beams to 10-20 micron spot sizes. This scheme circumvents limitations due to chromatic aberrations and space-charge effects in this relatively low energy (<100 Mev) system. The final focus scheme is based on an ultra-high gradient (300T/m) quadrupole which employs the Halbach 16-piece, permanent magnet design. Use of this optimized goemetry, NdFeB material, and a small (4 mm) bore allows the desired field gradient, and few cm focal length, to be achieved. The adjustability of the focusing system is obtained by changing the relative longitudinal positions of sub-component focusing and defocusing magnets on precision movers. We present the results of RADIA 3D design simulations, and measurement of prototype magnets. We also discuss the results of beam dynamics simulations of the PLEIADES system using both envelope and tracking codes. |
| title: | Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | R. England,P. Musumeci,R. Yoder,J. Rosenzweig |
| abstract: | We have recently added a dispersionless translating section to the UCLA Neptune linear accelerator beamline. This new section of beamline will serve as a venue for beam shaping and compression experiments using the 14MeV electron beam produced by the UCLA Neptune PWT linac and newly installed photoinjector. An examination of the first and second-order optics indicates that when certain nonlinear effects are minimized through the use of sextupole magnets, the longitudinal dispersion is dominated by a negative R56 which, for an appropriately chirped initial beam, can be used to create a ramped beam of a few picosecond duration that would be ideal for driving large amplitude wake fields in a plasma and producing high transformer ratios. The beamline is now in operation. Preliminary data indicate that the beamline optics are well-predicted by simulation and that sextupoles can be used successfully to eliminate nonlinear horizontal dispersion. Future experiments are planned for measuring beam compression (using CTR autocorrelation) and doing longitudinal phase space tomography (using a transverse deflecting cavity). |
| title: | Comparison of the coherent radiation-induced microbunching instability in a free-electron laser and a magnetic chicane |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 040702 |
| year: | 2003 |
| authors: | S. Reiche,J. Rosenzweig |
| abstract: | A self-amplified spontaneous emission free-electron laser (SASE FEL) is a device which is based on the creation of a very intense, relativistic electron beam which has very little temperature in all three phase planes. The beam in this system is described as having "high brightness,'' and when it is bent repetitively in a magnetic undulator, undergoes a radiation-mediated microbunching instability. This instability can amplify the original radiation amplitude at a particular, resonant wavelength by many orders of magnitude. In order to obtain high brightness beams, it is necessary to compress them to obtain higher currents than available from the electron source. Compression is accomplished by the use of magnetic chicanes, which are quite similar to, if much longer than, a single period of the undulator. It should not be surprising that such chicanes also support a radiation-mediated microbunching interaction, which has recently been investigated, and has been termed coherent synchrotron radiation (CSR) instability. The purpose of this paper is to compare and contrast the characteristics of the closely related FEL and CSR microbunching instabilities. We show that a high-gain regime of the CSR instability exists which is formally similar to the FEL instability. |
| title: | Design Considerations for a High-Efficiency High-Gain Free-Electron Laser for Power Beaming |
| conference: | 25th International Free Electron Laser Conference |
| year: | 2003 |
| authors: | C. Muller,G. Travish |
| abstract: | Power beaming from ground-based systems to space-based platforms has been proposed by a number of researchers as a means of delivering energy to orbiting satellites and stations. This paper considers the use of a seeded high-gain high-efficiency Free-Electron Laser (FEL) amplifier based on a conventional linac as the source for power beaming. While the wall-plug efficiency of a single pass FEL is likely to be considerably lower than a recirculating system, electrical efficiency is unlikely to be a serious consideration for first-generation power-beaming systems. Moreover, the simplicity of the proposed scheme scales well from existing and completed experiments. |
| title: | Design and Operation of Pegasus Thermionic Cathode |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | P. Frigola,G. Andonian,S. Reiche,J. Rosenzweig,S. Telfer,G. Travish |
| abstract: | A new thermionic cathode has been developed and installed for use on The PEGASUS plane wave transformer injector. The novel design of the LaB6 cathode allows for thermionic emission as well as photoinjector operation. Test stand measurements as well as in situ operational experience are reported. |
| title: | Design and Status of the VISA II Experiment |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | G. Andonian,R. Agustsson,A. Murokh,C. Pellegrini,S. Reiche,J. Rosenzweig,G. Travish,M. Babzien,I. Ben-Zvi,V. Yakimenko,L. Palumbo,C. Vicario |
| abstract: | VISA II is the follow-up project to the successful Visible to Infrared SASE Amplifier (VISA) experiment at the Accelerator Test Facility (ATF) in Brookhaven National Lab (BNL). This paper will report the motivation for and status of the two main experiments associated with the VISA II program. One goal of VISA II is to perform an experimental study of the physics of a chirped beam SASE FEL at the upgraded facilities of the ATF. This requires a linearization of the transport line to preserve energy chirping of the electron beam at injection. The other planned project is a strong bunch compression experiment, where the electron bunch is compressed in the chicane, and the dispersive beamline transport, allowing studies of deep saturation. |
| title: | Energy Loss and Accelerating Field in the Plasma Wakefield Accelerator |
| format: | unpublished |
| year: | 2003 |
| authors: | J. Rosenzweig,R. Yoder,N. Barov,M. Thompson |
| abstract: |
| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulation |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | J. Rosenzweig,N. Barov,M. Thompson,R. Yoder |
| abstract: |
| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulations, Scaling, and Accelerating Wakefields |
| format: | preprint |
| year: | 2003 |
| authors: | J. Rosenzweig,N. Barov,M. Thompson,R. Yoder |
| abstract: |
| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | N. Barov,J. Rosenzweig,M. Thompson,R. Yoder |
| abstract: |
| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis |
| format: | preprint |
| year: | 2003 |
| authors: | . |
| abstract: |
| title: | Generation of High Brightness X-Rays with the PLEIADES Thomson X-Ray Source |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | W. Brown,S. Anderson,C. Barty,J. Crane,R. Cross,D. Fittinghoff,F. Hartemann,J. Kuba,G. Le Sage,D. Slaughter,P. Springer,A. Tremaine,J. Rosenzweig,D. Gibson |
| abstract: | The use of short laser pulses to generate high peak intensity, ultra-short x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. PLEIADES (Picosecond Laser Electron InterAction for the Dynamic Evaluation of Structures) is a next generation Thomson scattering x-ray source being developed at Lawrence Livermore National Laboratory (LLNL). Ultra-fast picosecond x-rays (10-200 keV) are generated by colliding an energetic electron beam (20-100 MeV) with a high intensity, sub-ps, 800 nm laser pulse. The peak brightness of the source is expected to exceed 1020 photons/s/0.1 bandwidth/mm2/mrad2. Simulations of the electron beam production, transport, and final focus are presented. Electron beam measurements, including emittance and final focus spot size are also presented and compared to simulation results. Measurements of x-ray production are also reported and compared to theoretical calculations. |
| title: | Horizontal Phase-Space Distortions Arising from Magnetic Pulse Compression of an Intense, Relativistic Electron Beam |
| journal: | Physical Review Letters |
| vol-pages: | 074803 |
| year: | 2003 |
| authors: | S. Anderson,J. Rosenzweig,P. Musumeci,M. Thompson |
| abstract: | We report detailed measurements of the transverse phase space distortions induced by magnetic chicane compression of a high brightness, relativistic electron beam to subpicosecond length. A strong bifurcation in the phase space is observed when the beam is strongly compressed. This effect is analyzed using several computational models and is correlated to the folding of longitudinal phase space. The impact of these results on current research in collective beam effects in bending systems and implications for future short wavelength free-electron lasers and linear colliders are discussed. |
| title: | Measurements of nonlinear harmonic radiation and harmonic microbunching in a visible SASE FEL |
| conference: | 24th International Free Electron Laser Conference |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | A. Tremaine,X. Wang,M. Babzien,I. Ben-Zvi,M. Cornacchia,R. Malone,A. Murokh,H. Nuhn,C. Pellegrini,S. Reiche,J. Rosenzweig,J. Skaritka,V. Yakimenko |
| abstract: | The experimental characterization of nonlinear harmonic generation (NHG) and electron beam microbunching at saturation from a visible SASE FEL are presented in this report. The gain lengths, spectra and energies of NHG were experimentally measured up to the third harmonic, and agree with theoretical predictions. Electron beam microbunching in both the fundamental and the second harmonic as the function of the SASE output were experimentally observed over the full range of SASE gain. The bunching factors for both the fundamental (b(1)) and second harmonic (b(2)) were experimentally characterized at saturation. The microbunching data provides another test of SASE saturation as well as correlating the NHG and electron beam microbunching modes to the fundamental SASE. |
| title: | New Vacuum Chamber for the Plasma Density Transition-Trapping Experiment |
| format: | tech note |
| year: | 2003 |
| authors: | M. Schneider,M. Thompson |
| abstract: | The plasma density transition trapping experiment is designed to capture an electron beam and modify its quality (emittance, energy spread, and brightness) via a plasma wake-field [1]. The Particle Beam Physics Laboratory (PBPL) transition-trapping plasma experiment requires a chamber to support the confined plasma source, in-vacuum diagnostics and associated hardware. Initial measurements on the plasma source utilized a chamber initially created for an underdense plasma lens experiment [2]. However, current research and future positioning of the plasma source required drastic improvements of nearly all facets of the chamber design. The initial plan was to rearrange the plasma source to move the interaction box onto the opposite side of the pumping-Tee (see picture below). This proved successful to measure plasma densities at or above the required value to carry out the plasma transition-trapping experiment. However, because the original design of the interaction box did not have an exit port for the beamline, a new box design became necessary. A decision was made to redesign the plasma chamber from scratch. The proposed design and specifications are described in this note. |
| title: | Non-Resonant Beat-Wave Excitation of Constant Phase-Velocity, Relativistic Plasma Waves for Charged-Particle Acceleration |
| format: | preprint |
| year: | 2003 |
| authors: | C. Filip,R. Narang,S. Tochitsky,C. Clayton,P. Musumeci,R. Yoder,K. Marsh,J. Rosenzweig,C. Pellegrini,C. Joshi |
| abstract: |
| title: | Photocathode Emission: The effects of high bandwidth drive lasers on thermal emittance |
| format: | unpublished |
| year: | 2003 |
| authors: | G. Travish |
| abstract: |
| title: | Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | . |
| abstract: |
| title: | Properties of the ultrashort gain length, self-amplified spontaneous emission free-electron laser in the linear regime and saturation |
| journal: | Physical Review E |
| vol-pages: | 066501 |
| year: | 2003 |
| authors: | A. Murokh,R. Agustsson,M. Babzien,I. Ben-Zvi,L. Bertolini,K. Van Bibber,R. Carr,M. Cornacchia,P. Frigola,J. Hill,E. Johnson,L. Klaisner,G. Le Sage,M. Libkind,R. Malone,H. Nuhn,C. Pellegrini,S. Reiche,G. Rakowsky,J. Rosenzweig,R. Ruland,J. Skaritka,A. Toor,A. Tremaine,X. Wang,V. Yakimenko |
| abstract: | VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission (SASE) free-electron laser (FEL), which achieved saturation at 840 nm within a single-pass 4-m undulator. The experiment was performed at the Accelerator Test Facility at BNL, using a high brightness 70-MeV electron beam. A gain length shorter than 18 cm has been obtained, yielding a total gain of 2x10(8) at saturation. The FEL performance, including the spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. Results are compared to the three-dimensional SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL systems. An agreement between simulations and experimental results has been obtained at an unprecedented level of detail. |
| title: | Pulse Compression via Velocity Bunching with the LLNL Thomson X-Ray Source Photoinjector |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | S. Anderson,W. Brown,A. Tremaine,P. Musumeci,J. Rosenzweig |
| abstract: | We report the compression of a high brightness, relativistic electron beam to rms lengths below 300 femtoseconds using the velocity compression technique in the LLNL Thomson X-ray source photoinjector. The results are consistent with analytical and computational models of this process. The emittance evolution of the beam during compression is investigated in simulation and found to be controllable with solenoid focusing. |
| title: | Pulse Length Control in an X-Ray FEL by Using Wakefields |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | S. Reiche,P. Emma,C. Pellegrini |
| abstract: | For the users of the high-brightness radiation sources of free-electron lasers it is necessary to reduce the FEL pulse length to 10 fs and below for time-resolving pump and probe experiments. Although it can be achieved by conventional compression methods for the electron beam or the chirped FEL pulse, the technical realization is demanding. In this presentation we study the impact of undulator wakefields and how their properties can be used to reduced the amplifying part of the bunch to the desired length. Methods of actively controlling the wakefields are presented. |
| title: | Pulse length control in an X-ray FEL by using wakefields |
| conference: | 24th International Free Electron Laser Conference |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | S. Reiche,P. Emma,C. Pellegrini |
| abstract: | For the users of the high-brightness radiation sources of free-electron lasers it is desirable to reduce the FEL pulse length to 10 fs and below for time-resolving pump and probe experiments. Although it can be achieved by conventional compression methods for the electron beam or the chirped FEL pulse, the technical realization is demanding. In this presentation we study the impact of longitudinal wakefields in the undulator and how their properties can be used to reduced the amplifying part of the bunch to the desired length. Methods of actively controlling the wakefields are presented. |
| title: | Results of the VISA SASE FEL Experiment at 840 nm |
| conference: | 24th International Free Electron Laser Conference |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | A. Murokh,R. Agustsson,M. Babzien,I. Ben-Zvi,L. Bertolini,K. Van Bibber,R. Carr,M. Cornacchia,P. Frigola,J. Hill,E. Johnson,L. Klaisner,G. Le Sage,M. Libkind,R. Malone,H. Nuhn,C. Pellegrini,S. Reiche,G. Rakowsky,J. Rosenzweig,R. Ruland,J. Skaritka,A. Toor,A. Tremaine,X. Wang,V. Yakimenko |
| abstract: | VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission (SASE) free-electron laser (FEL), which achieved saturation at 840 nm within a single-pass 4-m undulator. A gain length shorter than 18 cm has been obtained, yielding the gain of 2x10(8) at saturation. The FEL performance, including the spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. The results are compared to 3-D SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL system. Detailed agreement between simulations and experimental results is obtained over the wide range of the electron beam parameters. |
| title: | Start to End Simulations for the SPARX Proposal |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | M. Biagini,M. Boscolo,M. Ferrario,V. Fusco,S. Guiducci,B. Spataro,C. Vaccarezza,M. Zobov,L. Serafini,R. Bartolini,G. Dattoli,L. Giannessi,L. Mezi,M. Quattromini,C. Ronsivalle,E. Chiadroni,P. Emma,J. Rosenzweig |
| abstract: | The resource allocation in the Italian National Research Plan (PNR) for the development of a coherent ultra-brilliant X-ray source, based on a SASE Free Electron Laser, brought about the formation of a CNR-ENEA-INFN- University of Roma "Tor Vergata" study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated leading to the SPARX proposal. We report in this paper the results of start to end simulations concerning the option based on an S-band normal conducting linac. Saturation at 1-10 nm can be achieved in a 40 m long undulator provided the peak current delivered by the linac is 2.5 kA at 2.5 GeV with rms normalized slice emittance of the order of 1 _m and the energy spread less than 0.1%. One of the most critical systems is the bunch compressor. The effects on beam dynamics of a magnetic chicane system and a rectilinear RF compressor (based on velocity bunching), integrated in a high brightness photoinjector, are analyzed and compared in this paper. |
| title: | Start-to-End Simulations for the LCLS X-Ray Free-Electron Laser |
| conference: | 25th International Free Electron Laser Conference |
| year: | 2003 |
| authors: | S. Reiche,C. Pellegrini,P. Emma,H. Nuhn,C. Limborg,M. Borland,W. Fawley |
| abstract: | The LCLS Free-Electron Lasers operates in the wavelength range of 1.5-15 Angstrom, using an electron beam with an energy between 4.5 and 14.5 GeV. The generation of the electron beam, the preservation of its brightness during acceleration and compression, and the amplififcation of the spontaneous radiation within the FEL can only be described by a consistent set of simulation codes. We preset the change in the FEL performance with respect to the LCLS design case, when various effects are included, altering the electron beam distribution and motion (e.g. wake fields, CSR, magnet misalignment or field errors of the undulator field). To distinguish the individual contribution of each effect, multiple start-end simulations are performed, including step by step additional effects and, thus, approaching a more and more realistic model of the LCLS FEL. |
| title: | Status of the Inverse Free Electron Laser Experiment at the Neptune Laboratory |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | P. Musumeci,C. Pellegrini,J. Rosenzweig,S. Tochitsky,G. Travish,R. Yoder,A. Varfolomeev,S. Tolmachev,A. Varfolomeev,T. Yarovoi |
| abstract: | We report on the status of the Inverse Free Electron Laser accelerator experiment under construction at the UCLA Neptune Laboratory. This experiment will use a 400 GW CO2 laser to accelerate through a tapered undulator an electron beam from 14.5 MeV up to 55 MeV. The scheme proposed is the diffraction dominated IFEL interaction where the Rayleigh range of the laser beam is 3.5 cm, much shorter than the interaction length (the undulator length is 50 cm). The undulator is strongly tapered in both field and period. The present status of the experiment is reported. |
| title: | Status of the UCLA PEGASUS Injector Laboratory |
| conference: | 24th International Free Electron Laser Conference |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | G. Andonian,S. Telfer,S. Reiche,J. Rosenzweig,P. Frigola |
| abstract: | The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Initial operations show a 15 MeV dark current beam that will be used for beam radiation studies. The design of a new LaB_6 cathode will allow for both thermionic emission and photoinjection operation. Experiments currently planned include novel beam instrumentation, surface effects in optical transition radiation, and waveguide SASE FEL. |
| title: | Status of the UCLA PEGASUS Laboratory |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | G. Andonian,P. Frigola,S. Reiche,J. Rosenzweig,S. Telfer,G. Travish |
| abstract: | The PEGASUS laboratory is a versatile radiation facility dedicated to the advancement of novel concepts in beam physics. The installation of a new LaB$_6$ cathode will allow for both thermionic emission and photoinjection operation. The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Recent operations show a 15 MeV dark current beam that will be used for beam radiation studies. An upgrade to the drive laser system has been explored and will be realized shortly. This paper will describe and report the status of the various subsystems of the PEGASUS laboratory and outline the experiments underway, such as innovative beam instrumentation, surface effects in optical transition radiation, Thomson scattering, and waveguide SASE FEL. |
| title: | The FEL Program at the PEGASUS Injector |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | S. Reiche,G. Andonian,P. Frigola,J. Rosenzweig,S. Telfer,G. Travish |
| abstract: | The PEGASUS photo injector at UCLA can produce a photo electrons beam with a normalized emittance of 2 mm mrad at an energy of 12-15 MeV, capable of driving a Free-Electron Laser in the mid IR regime. The FEL program, associated with the PEGASUS injector and presented here, is based on a Self-Amplifying Spontaneous Emission (SASE) FEL. The studies focus on increasing the efficiency of an FEL by novel undulator design and compensation of diffraction effects, using waveguides of millimeter size. In this presentation we also discuss the possibility of the PEGASUS FEL as a THz user facility. |
| title: | The ORION Facility |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | R. Noble,E. Colby,D. Palmer,R. Siemann,D. Walz,R. Byer,C. Joshi,W. Mori,J. Rosenzweig,T. Katsouleas |
| abstract: | ORION will be a user-oriented research facility for understanding the physics and developing the technology for future high-energy particle accelerators. The ORION Facility will bring together the needed resources for performing a wide range of experiments in advanced accelerator and beam physics. The facility has as its centerpiece the Next Linear Collider Test Accelerator (NLCTA) within End Station B at the SLAC Central Research Yard. That site will be modified with the addition of a new high-brightness photoinjector, its associated drive laser and rf power system, a user laser room, a low-energy experimental hall supplied with electron beams up to approximately 60 MeV in energy, and a high-energy hall supplied with beams up to 350 MeV. Facility construction is anticipated to start in October 2003, contingent upon funding approval, and first beam is planned for 2005. The first experiment at ORION, the laser acceleration experiment E163, has been approved by SLAC. In this paper, results are presented on the revised facility layout and design which came out of the 2nd ORION Workshop in February 2003, and the beam physics design of the injector and the beamlines for the low and high-energy experimental halls. |
| title: | The UCLA Pegasus Plane-Wave Transformer Photoinjector |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | G. Travish,G. Andonian,P. Frigola,S. Reiche,J. Rosenzweig,S. Telfer |
| abstract: | A photoinjector based on a multicell plane wave transformer accelerating structure has been commissioned at the UCLA Department of Physics' Pegasus Laboratory. Design and construction of the novel structure have been previously reported [J. Rosenzweig, et al. PAC Proceedings 1997], and recent operation with a thermionic cathode is being presented at this conference [P. Frigola, et al. these proceedings]. This paper describes the planned operation of the PWT gun as a photoinjector, including design and construction details of the drive laser. Progress to date and future plans are discussed. |
| title: | The UCLA/NICADD Plasma Density Transition Trapping Experiment |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | M. Thompson,W. Lu,W. Mori,J. Rosenzweig,G. Travish,N. Barov |
| abstract: | Plasma density transition trapping is a recently purposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. Two and three dimensional Particle-In-Cell (PIC) simulations show that electron beams of substantial charge can be captured using this technique, and that the beam parameters such as emittance, energy spread, and brightness can be optimized by manipulating the plasma density profile. These simulations also predict that transition trapping can produce beams with brightness > 5x10^14 Amp/(m-rad)^2 when scaled to high plasma density regimes. A proof-of-principle plasma density transition trapping experiment is planned for the near future. This experiment is a collaboration between UCLA and the Northern Illinois University (NICADD). The goal of experiment is to capture a ~100 pC beam with ~4% rms energy spread out of a 2 x 10^13 cm^-3 peak density plasma using a ~6nC, 14 MeV drive beam. Status and progress on the experiment are reported. |
| title: | Theoretical evaluation of the LCLS X-Ray Free-Electron Laser performance |
| conference: | 25th International Free Electron Laser Conference |
| year: | 2003 |
| authors: | S. Reiche,C. Pellegrini,P. Emma,H. Nuhn |
| abstract: | In this paper we evaluate the performance of the LCLS FEL, including all known physical effects from the electron source to the undulator exit which determine the X-ray pulse characteristics. The wavelength range considered is from the 15 to 1.5 Angstrom, with an extension to 0.5 Angstrom using the third harmonic. The results of this work have been useful to identify areas in the LCLS design where improvements could be made, thus optimizing the system performance. |
| title: | Tunneling Ionization Bunch Length Monitor for the Ultrarelativistic Compressed Electron Beams |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | A. Murokh |
| abstract: | The electric field intensity of the compressed ultra-relativistic electron beams is approaching GV/m levels, which is sufficient to cause observable tunneling effect in the low band gap materials. In this article the tunneling ionization rate is estimated for the experimentally available electron beam parameters, and a proposed proof of principle experiment is outlined. Tunneling effect has exponential dependence on the electric field strength; thus being very sensitive to the electron beam peak current. This non-linear dependence opens up a possibility to construct inexpensive, single shot and non-destructive peak current diagnostics for the ultrarelativistic compressed electron beams. |
| title: | Velocity Bunching Experiment at the Neptune Laboratory |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| authors: | P. Musumeci,R. Yoder,J. Rosenzweig |
| abstract: | In this paper we describe the rectilinear compression experiment at the Neptune photoinjector at UCLA. The electron bunches have been shortened to sub-ps pulse length by chirping the beam energy spectrum in a short S-band high gradient standing wave RF cavity and then letting the electrons undergo velocity compression in the following rectilinear drift. Using a standard Martin Puplett interferometer to characterize coherent transition radiation from the beam, we measured bunch lengths as short as 0.4 ps with compression ratio in excess of 10 for an electron beam of 7 MeV energy and charge up to 300 pC. |
| title: | Velocity bunching experiment at the Neptune Laboratory |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year published: | 2003 |
| year authored: | 2002 |
| authors: | . |
| abstract: |
| title: | X-ray free-electron lasers- principles, properties and applications |
| journal: | Nuclear Instruments & Methods A |
| vol-pages: | 33-40 |
| year: | 2003 |
| authors: | C. Pellegrini,J. Stoehr |
| abstract: | With advances in technology, it is now possible to realize the dream of fully coherent X-ray laser. |
| title: | A Resonant, THz Slab-Symmetric Dielectric-Based Accelerator |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| authors: | R. Yoder,J. Rosenzweig |
| abstract: |
| title: | A THz radiation driven IFEL as a phaselocked prebuncher for a plasma beat-wave accelerator |
| conference: | International Conference on Lasers 2001 |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | P. Musumeci,S. Tochitsky,C. Clayton,C. Joshi,C. Pellegrini,J. Rosenzweig |
| abstract: | To obtain a high quality electron beam with small energy spread in the laser driven plasma accelerator, the electrons have to be prebunched at the scale of the plasma wavelength. We study the feasibility of an experiment where an inverse free electron laser (IFEL) is used to bunch the electron beam before the injection into a plasma beatwave accelerator. It is suggested to drive the IFEL prebuncher by a THz seed radiation phase-locked to the electromagnetic beatwave through difference frequency generation process in a nonlinear crystal. Design and numerical simulations for this experiment are presented. |
| title: | An undulator with nonadiabatic tapering for the IFEL project |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | A. Varfolomeev,S. Tolmachev,T. Yarovoi,P. Musumeci,C. Pellegrini,J. Rosenzweig |
| abstract: | We describe the design of a planar undulator with unusually strong tapering, for the inverse FEL experiment (on the IFEL experiment at the UCLA Neptune Lab. Presented at the 2001 Particle Accelerator Conference, June 18-22, 2001, Chicago, Illinois) to be carried out in Neptune Lab. (Nucl. Instr. and Meth. A 410 (1998) 437) at UCLA. A powerful TW CO_2 laser will be used to accelerate electrons up to 50-60 MeV in 50 cm long undulator. A strong undulator tapering is needed because of the short Rayleigh length of the laser beam. Both the magnetic field and the undulator period are tapered to provide synchronicity of the laser beam interaction with a captured electron bunch along the whole undulator length. The most critical part of the undulator is the region near the laser focus. The main characteristics of the IFEL, such as the percentage of trapped electrons, energy of accelerated electrons and sensitivity to the laser focus transverse position, are given. The general principles of the design of this undulator construction can also be useful for high efficiency FEL amplifiers of intense laser modes. |
| title: | Beam extraction studies at 900 GeV using a channeling crystal |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 043501 |
| year: | 2002 |
| authors: | R. Carrigan,D. Chen,G. Jackson,N. Mokhov,C. Murphy,S. Baker,S. Bogacz,D. Cline,S. Ramachandran,J. Rhoades,J. Rosenzweig,A. Asseev,R. Biryukov,A. Taratin,J. Ellison,A. Khanzadeev,T. Prokofieva,V. Samsonov,G. Solodov,B. Newberger,E. Tsyganov,H. Shih,W. Gabella,B. Cox,V. Golovatyuk,A. McManus |
| abstract: | Luminosity-driven channeling extraction has been observed for the first time in a 900 GeV study at the Fermilab Tevatron. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multipass extraction was found to increase the efficiency of the process significantly. The beam extraction efficiency was about 25%. Studies of time dependent effects found that the turn-to-turn structure was governed mainly by accelerator beam dynamics. Based on the results of this experiment, it is feasible to construct a parasitic 5?10 MHz proton beam from the Tevatron collider. |
| title: | Characterization of an 800 nm SASE FEL at saturation |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | A. Tremaine,P. Frigola,A. Murokh,C. Pellegrini,S. Reiche,J. Rosenzweig,M. Babzien,I. Ben-Zvi,E. Johnson,R. Malone,G. Rakowsky,J. Skaritka,X. Wang,K. Van Bibber,L. Bertolini,J. Hill,G. Le Sage,M. Libkind,A. Toor,R. Carr,M. Cornacchia,L. Klaisner,H. Nuhn,R. Ruland |
| abstract: | Visible to Infrared SASE Amplifier is a free electron laser (FEL) designed to saturate at a radiation wavelength of 800 nm within a 4 m long, strong focusing undulator. A large gain is achieved by driving the FEL with 72 MeV, high brightness beam of BNL's accelerator test facility. We present measurements that demonstrate saturation in addition to the frequency spectrum of the FEL radiation. Energy, gain length and spectral characteristics are compared and shown to agree with simulation and theoretical predictions. (16 References). |
| title: | Chirped-beam two-stage SASE-FEL for high power femtosecond X-ray pulse generation |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | C. Schroeder,C. Pellegrini,S. Reiche,J. Arthur,P. Emma |
| abstract: | A method for generating femtosecond duration X-ray pulses using a single-pass free-electron laser (FEL) is presented. This method uses an energy-chirped electron beam propagating through an undulator to produce a frequency-chirped X-ray pulse through self-amplified spontaneous emission (SASE). After the undulator, we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse; therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped-beam two-stage SASE?FEL, and consider the performance of the chirped-beam two-stage option for the Linac Coherent Light Source. |
| title: | Chirped-beam two-stage free-electron laser for high-power femtosecond x-ray pulse generation |
| journal: | Journal of the Optical Society of America B-Optical Physics |
| vol-pages: | 1782-89 |
| year: | 2002 |
| authors: | C. Schroeder,C. Pellegrini,S. Reiche,J. Arthur,P. Emma |
| abstract: | A method for generating femtosecond-duration x-ray pulses with a free-electron laser is presented. This method uses an energy-chirped electron beam propagating through an undulator to produce a frequency-chirped x-ray pulse by self-amplified spontaneous emission. A short temporal pulse is created by use of a monochromator to select a narrow radiation bandwidth. A second undulator is used to amplify the short-duration radiation. The radiation characteristics produced by a chirped-beam two-stage free-electron laser are calculated, and the performance of the chirped-beam two-stage option for the Linac Coherent Light Source is considered. |
| title: | Creation, Manipulation, and Diagnosis of Intense, Relativistic Picosecond Photo-electron Beams |
| format: | thesis |
| year: | 2002 |
| authors: | S. Anderson |
| abstract: | The radio frequency photoinjector is the pre-eminent source for advanced electron beam applications that require extremely high phase space density (high brightness) beams. Because of their high phase space density, the collective fields generated by photoinjector beams dominate their behavior. These space-charge fields influence every aspect of the beam's handling, including its acceleration, measurement, and transport. The effects of spece-charge must be carefully considered in all of these beam handling procedures in order to deliver the highest brightness beams possible. This dissertation investigates the space-charge dominated physical processes involved in the acceleration and propagation, emittance measurement, and magnetic compression fo photoinjector beams. In the analysis of the behavior of these beams, emphasis is placed on the techniques used to compensate for space-charge forces, and maximize beam brightness. The rectilinear motion of a space-charge cominated beam is analyzed, including both linear and nonlinear self forces, in order to determine the evolution of the beam's transverse emittance as it is accelerated and transported through the photoinjector. It is found that the emittance can be made to oscillate by judicious use of external forces, and that this oscillation can be manipulated to minimize the beam's emittance, compensating for the effects of both linear and nonlinear space-charge forces, at a given location of interest. The creation of a high brightness beam in the presence of emittance oscillations is critically dependent on phase space diagnosis. Thus the measurement of emittance of intense beams is investigated experimentally, theoretically, and in simulation, for quadrupole scanning and multi-slit based measurement techniques. The quadrupole scanning method is found to have systematic errors for space-charge dominated beams, and experimental measurements using this technique give consistently higher emittance values than both the slit-based measurements and simulations. Finally, the measurement of emittance growth and transverse phase space distortions induced by magnetic compression of the beam to sub-picosecond lengths is described. A clear bifurcation of the phase space is observed when the beam is strongly compressed. This effect is found to be correlated to the folding of the beam distribution in configuration space. |
| title: | Experimental Characterization of the Saturating, Near Infrared, Self-Amplified Spontaneous Emission Free Electron Laser: Anayasis of Radiation Properties and Electron beam Dynamics |
| format: | thesis |
| year: | 2002 |
| authors: | A. Murokh |
| abstract: | In this work, the main results of the VISA experiment (Visible to Infrared SASE Amplifier) are presented and analyzed. The purpose of the experiment was to build a state-of-the-art single pass self-amplified spontaneous emission (SAS) free electron laser (FEL) based on a high brightness electron beam, and characterize its operation, including saturation, in the near infrared spectral region. This experiment was hosted by Accelerator Test Facility (ATF) at Brookhaven National laboratory, which is a users facility that provides high brightness relativistic electron beams generated with the photoinjector. During the experiment, SASE FEL performance was studied in two regimes: a long bunch, lower gain operation; and a short bunch high gain regime. The transition between the two conditions was possible due to a novel bunch compressionmechanism, which was discovered in teh course of the experiment. This compression allowed the variation fo peak current in teh electron beam before it was launched into the 4-m VISA undulator. In the long bunch regime, a SASE FEL power gain length of 29 cm was obtained, and the generated radiation spectral and statistical properties were characterized. In the short bunch regime, a power gain length of under 18 cm was achieved at 842 nm, which is at least a factor of two shorter than ever previously achieved in this spectral range. Further, FEL saturation was obtained before the undulator exit. The FEL system's performance was measured along the length of the VISA undulator, and in the final state. Statistical, spectral and angular properties of the short bunch SASE radiation have been measured int eh exponential gain regime, and at saturation. One of the most important aspects of the data analysis presented in this thesis was the development and use of start-to-end numerical simulations of the experiment. The dynamics of the ATF electron beam was modeled starting from teh photocathode, through acceleration, transport, and inside the VISA undulator. The model allowed simulation SASE process for different beam conditions, including the effects of the novel bunch compression mechanism on the electron beam 6-D phase space distribution. The numberical simulations displayed an excellent agreement with the experimental data, and became key to understanding cimplex dynamics of the SASE FEL process at VISA. |
| title: | Experimental characterization of nonlinear harmonic radiation from a visible self-amplified spontaneous emission free-electron laser at saturation |
| journal: | Physical Review Letters |
| vol-pages: | 204801 |
| year: | 2002 |
| authors: | A. Tremaine,X. Wang,M. Babzien,I. Ben-Zvi,M. Cornacchia,H. Nuhn,R. Malone,A. Murokh,C. Pellegrini,S. Reiche,J. Rosenzweig,V. Yakimenko |
| abstract: | Nonlinear harmonic radiation was observed using the VISA self-amplified, spontaneous emission (SASE) free-electron laser (FEL) at saturation. The gain lengths, spectra, and energies of the three lowest SASE FEL modes were experimentally characterized. The measured nonlinear harmonic gain lengths and center spectral wavelengths decrease with harmonic number, n, which is consistent with nonlinear harmonic theory. Both the second and third nonlinear harmonics energies are about 1% of the fundamental energy. These experimental results demonstrate for the first time the feasibility of using nonlinear harmonic SASE FEL radiation to produce coherent, femtosecond X-rays. (33 References). |
| title: | Fundamental and Harmonic Microbunching Measurements in a High-Gain, Self-Amplified, Spontaneous Emission Free-Electron Laser |
| format: | preprint |
| year: | 2002 |
| authors: | A. Tremaine,X. Wang,M. Babzien,I. Ben-Zvi,M. Cornacchia,A. Murokh,H. Nuhn,R. Malone,C. Pellegrini,S. Reiche,J. Rosenzweig,J. Skaritka,V. Yakimenko |
| abstract: | The self-amplified, spontaneous emission free-electron laser (SASE-FEL) gain process is a collective instability which induces microbunching in the electron beam. Micro-bunching approaching unity at the fundamental FEL wavelength (845 nm), and its second harmonic, have been measured at the VISA FEL, at or near saturation. These measurements, which use the beam's coherent transition radiation (CTR) spectrum, are sompared to the predictions of FEL simulations. Comparison of shot-by-shot SASE and CTR signals firmly establishes the role of SASE in the development of microbunching harmonics. |
| title: | Fundamental and harmonic microbunching in a high-gain self-amplified spontaneous-emission free-electron laser |
| journal: | Physical Review E |
| vol-pages: | 036503 |
| year: | 2002 |
| authors: | A. Tremaine,X. Wang,M. Babzien,I. Ben-Zvi,M. Cornacchia,A. Murokh,H. Nuhn,R. Malone,C. Pellegrini,S. Reiche,J. Rosenzweig,J. Skaritka,V. Yakimenko |
| abstract: | Electron beam microbunching in both the fundamental and second harmonic in a high-gain self-amplified spontaneous emission free-electron laser (SASE FEL) was experimentally characterized using coherent transition radiation. The microbunching factors for both modes (b1 and b2) approach unity, an indication of FEL saturation. These measurements are compared to the predictions of FEL simulations. The simultaneous capture of the microbunching and SASE radiation for individual micropulses correlate the longitudinal electron beam structure with the FEL gain. |
| title: | Inverse Free Electron Laser Experiment at the Neptune Laboratory |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| authors: | P. Musumeci,C. Pellegrini,J. Rosenzweig,A. Varfolomeev,S. Tolmachev,T. Yarovoi |
| abstract: | We present an Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Laboratory. This experiment will use a 1 TW CO2 laser to accelerate through two strongly tapered undulators an electron beam from 16 MeV up to 5 MeV. The scheme proposed is the diffraction dominated IFEL interaction. The Raleigh range of the laser beam is about 2 cm, much shorter than the interaction length (the undulator length is 50 cm). In this regime adiabatic capture is possible in the first part of the undulator. In the focus region, we propose a solution to the problem of the dephasing between electrons and photons due to the |
| title: | PEGASUS Safety Interlock System |
| format: | tech note |
| year: | 2002 |
| authors: | G. Andonian |
| abstract: | Describes the design and functioning of the safety interlock system in the PEGASUS lab. |
| title: | Photoinjector design for the LCLS |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | P. Bolton,J. Clendenin,D. Dowell,M. Ferrario,A. Fisher,S. Gierman,R. Kirby,P. Krejcik,C. Limborg,G. Mulhollan,D. Nguyen,D. Palmer,J. Rosenzweig,J. Schmerge,L. Serafini,X. Wang |
| abstract: | The design of the Linac Coherent Light Source assumes that a low-emittance, 1 nC, 10 ps beam will be available for injection into the 15 GeV linac. The proposed RF photocathode injector that will meet this requirement is based on a 1.6-cell S-band RF gun equipped with an emittance-compensating solenoid. The booster accelerator with a gradient of 25 MV/m is positioned at the beam waist coinciding with the first emittance maximum, i.e., the "new working point." The UV pulses required for cathode excitation will be generated by tripling the output of a Ti:sapphire laser system. Details of the design and the supporting simulations are presented. (12 References). |
| title: | Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| authors: | M. Thompson,J. Rosenzweig |
| abstract: |
| title: | Plasma Wakefield Experiments |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| authors: | N. Barov,M. Thompson,K. Bishofberger,J. Rosenzweig,H. Edwards,J. Santucci |
| abstract: |
| title: | Plasma electron fluid motion and wave breaking near a density transition |
| journal: | Physical Review E |
| vol-pages: | 016501 |
| year: | 2002 |
| authors: | R. England,J. Rosenzweig,N. Barov |
| abstract: | Recently, Suk, Barov, and Rosenzweig [Phys. Rev. Lett. 86, 1011 (2001)] proposed a scheme for trapping background electrons in a plasma wake field using a sudden downward transition in the background ion density, where the density transition length is small compared to the plasma skin depth. In the present paper we present a fluid dynamical description of this mechanism that is self-consistent up to the point of wave breaking. A one-dimensional nonlinear relativistic second-order differential equation is derived for the electron fluid velocity in Lagrangian coordinates. Numerical integrations of this equation are used to map out the regions of parameter space in which wave breaking occurs and to determine the extent of the downstream region of plasma involved in wave breaking. Comparisons with one-dimensional particle-in-cell (PIC) simulations show that the onset of trapping occurs at the parameter values where wave breaking begins in the fluid analysis, but that the downstream extent of plasma involved in wave breaking is not a reliable predictor of the number of trapped particles. The PIC simulations also reveal that particles initially located on the upstream side of the density transition may become trapped, although these particles do not participate in wave breaking in the fluid description. |
| title: | Self-amplified spontaneous emission saturation at the Advanced Photon Source free-electron laser |
| journal: | Review of Scientific Instruments |
| vol-pages: | 1407 |
| year: | 2002 |
| authors: | E. Moog,S. Milton,N. Arnold,C. Benson,W. Berg,S. Biedron,M. Borland,Y. Chae,R. Dejus,P. Den Hartog,B. Deriy,M. Erdmann,E. Gluskin,Z. Huang,K. Kim,J. Lewellen,Y. Li,A. Lumpkin,O. Makarov,A. Nassiri,V. Sajaev,R. Soliday,B. Tieman,E. Trakhtenberg,G. Travish,I. Vasserman,N. Vinokurov,G. Wiemerslage,B. Yang |
| abstract: | Today, many bright photon beams in the ultraviolet and x-ray wavelength range are produced by insertion devices installed in specially designed third-generation storage rings. There is the possibility of producing photon beams that are orders of magnitude brighter than presently achieved at synchrotron sources, by using self-amplified spontaneous emission (SASE). At the Advanced Photon Source (APS), the low-energy undulator test line (LEUTL) free-electron laser (FEL) project was built to explore the SASE process in the visible through vacuum ultraviolet wavelength range. While the understanding gained in these experiments will guide future work to extend SASE FELs to shorter wavelengths, the APS FEL itself will become a continuously tunable, bright light source. Measurements of the SASE process to saturation have been made at 530 and 385 nm. A number of quantities were measured to confirm our understanding of the SASE process and to verify that saturation was reached. The intensity of the FEL light was measured versus distance along the FEL, and was found to flatten out at saturation. The statistical variation of the light intensity was found to be wide in the exponential gain region where the intensity is expected to be noisy, and narrower once saturation was reached. Absolute power measurements compare well with GINGER simulations. The FEL light spectrum at different distances along the undulator line was measured with a high-resolution spectrometer, and the many sharp spectral spikes at the beginning of the SASE process coalesce into a single peak at saturation. The energy spread in the electron beam widens markedly after saturation due to the number of electrons that transfer a significant amount of energy to the photon beam. Coherent transition radiation measurements of the electron beam as it strikes a foil provide additional confirmation of the microbunching of the electron beam. The quantities measured confirm that saturation was indeed reached. Details are given in Milton et al., Science 292, 2037 (2001) (also online at www.sciencexpress.org as 10.1126/science. 1059955, 17 May 2001), and Lewellen et al., "Present Status and Recent Results from the APS SASE FEL," to be published in the Proceedings of the 23rd International Free-Electron Laser Conference, Darmstadt, Germany, 20?24 August 2001. |
| title: | Some Performance Parameters and Figures of Merit for Photoinjector Drive Lasers |
| format: | unpublished |
| year: | 2002 |
| authors: | G. Travish |
| abstract: |
| title: | Space-charge effects in high brightness electron beam emittance measurements |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 014201 |
| year: | 2002 |
| authors: | S. Anderson,J. Rosenzweig,G. Le Sage,J. Crane |
| abstract: | The measurement of emittance in space-charge dominated, high brightness beam systems is investigated from conceptual, computational, and experimental viewpoints. As the self-field-induced collective motion in the low energy, high brightness beams emitted from photoinjector rf guns are more important in determining the macroscopic beam evolution than thermal spreads in transverse velocity; traditional methods for phase space diagnosis fail in these systems. We discuss the role of space charge forces in a traditional measurement of transverse emittance, the quadrupole scan. The mitigation of these effects by use of multislit- or pepper-pot-based techniques is explained. The results of a direct experimental comparison between quadrupole scanning and slit-based determination of the emittance of a 5 MeV high brightness electron beam are presented. These data are interpreted with the aid of both envelope and multiparticle simulation codes. It is shown that the ratio of the beam's beta function to its transverse plasma wavelength plays a central role in the quadrupole scan results. Methods of determining the presence of systematic errors in quadrupole scan data are discussed. |
| title: | Start-to-end simulation for the LCLS X-ray FEL |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | . |
| abstract: | X-ray FELs, such as the LCLS and TESLA FEL, require electron beams with large peak current and very small emittance. The X-ray peak power, temporal and spectral properties, depend significantly on details of the electron beam phase space distribution. The electron beam distribution is determined by many effects, as the emission process at the gun photo-cathode, bunch compression, acceleration and wakefields within the undulator. Although analytical results can give an estimate of the expected performance, the complexity of the electron beam generation, acceleration and compression can only be evaluated using a numerical simulation of all these processes, a start-to-end simulation. In this presentation we discuss the LCLS X-Ray FEL performance estimated by a start-to-end simulation, and we compare the results with those obtained using a simpler model. (20 References). |
| title: | Status of the 3D Time-Dependent FEL Simulation Code GENESIS 1.3 |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | S. Reiche,B. Faatz |
| abstract: | Since its release in 1999 the 3D time-dependent code GENESIS 1.3 has become a helpful tool for the design-studies and analysis of a single-pass Free-Eelectron Lasers experiments. With the latest version new features have been added such as support for wake-fields and incoherent spontaneous radiation. In addition the more modular structure of the open-source code and the improved support of external imput files allow a better understanding of the code, supporting users who want to add new features to the code. |
| title: | The BESSY FEL Project |
| conference: | 23rd International Free Electron Laser Conference |
| year published: | 2002 |
| year authored: | 2001 |
| authors: | M. Abo-Bakr,W. Anders,J. Bahrdt,R. Bakker,W. Eberhardt,B. Faatz,R. Follath,A. Gaupp,M. Hartrott,E. Jaeschke,D. Kraemer,P. Kuske,M. Martin,R. Mueller,H. Prange,S. Reiche,W. Sandner,F. Senf,I. Will,G. Wustefeld |
| abstract: | Berliner Elektronenspeicherring-Gesellschaft fur Synchrotronstrahlung (BESSY) plans to construct a linac-based single-pass FEL as an addition to its existing third generation storage-ring-based light-source. The project aims to obtain an FEL-based user-facility that covers the VUV and soft X-ray spectral range (20 eV less than or equal to homega less than or equal to 1 keV). At present, the design stage is funded as a collaboration between BESSY, DESY, the Hahn-Meitner-Institute in Berlin, and the Max-Born-Institute in Berlin. This stage focuses on optimization of the FEL as a user light-source, both with respect to its capabilities and in its performance. Important issues are: stability, seeding options of the SASE FEL, wavelength-tunability, synchronization with external laser sources and, on a longer time-scale, the generation of ultra-short (< 20 fs RMS) optical pulses. |
| title: | Ultrafast materials probing with the LLNL Thomson X-ray source |
| conference: | 2002 Linear Accelerator Conference |
| year: | 2002 |
| authors: | A. Tremaine,S. Anderson,W. Brown,C. Barty,R. Cauble,J. Crane,H. Cynn,C. Ebbers,D. Fittinghoff,D. Gibson,F. Hartemann,I. Jovanovich,J. Kuba,G. Le Sage,A. McMahan,R. Minich,J. Moriarty,B. Remington,D. Slaughter,P. Springer,F. Steitz,C. Yoo,J. Rosenzweig,T. Ditmire |
| abstract: | The use of short laser pulses to generate very high brightness, ultra short (fs to ps) x-ray pulses is a topic of great interest. In principle, femtosecond-scale pump-probe experiments can be used to temporally resolve structural dynamics of materials on the time scale of atomic motion. The development of sub?ps x-ray pulses will make possible a wide range of materials and plasma physics studies with unprecedented time resolution. PLEIADES (Picosecond Laser Electron Interaction for Dynamic Evaluation of Structures), the Thomson scattering project at LLNL, will provide such a novel x-ray source of high power using short laser pulses and a high brightness, relativistic electron bunch. The system is based on a 5 mm-mrad normalized emittance photoinjector, 100 MeV electron RF linac, and a 300 mJ, 35 fs solid-state laser system. PLEIADES will produce ultra fast pulses with x-ray energies (60 keV) capable of probing into high-Z metals. |
| title: | Velocity bunching experiment at the Neptune Laboratory |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| authors: | P. Musumeci,R. England,M. Thompson,R. Yoder,J. Rosenzweig |
| abstract: |
| title: | Beam collimation for LCLS beam emittance and charge control |
| conference: | 19th ICFA Beam Dynamics Workshop on Physics of, and Science with, the X-Ray Free-Electron Laser |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | C. Schroeder,H. Nuhn,C. Pellegrini |
| abstract: | We describe an electron beam collimator for the linac coherent light source (LCLS). The collimator reduces both the transverse emittance and the total charge of the electron beam. Beam optics are designed to increase the beam spot size for collimation. The impedance of the collimator is calculated, and the wakefield induced emittance growth is determined. (12 References). |
| title: | Beam-plasma interaction experiments at the UCLA Neptune Laboratory |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | M. Thompson,C. Clayton,J. England,J. Rosenzweig,H. Suk |
| abstract: | We are currently planning several beam-plasma interaction experiments using the high quality 16 MeV electron beam produced by the Neptune 1.625-cell photoinjector and PWT linac. The underdense (n_b > n_0) plasma lens experiment will examine the focusing of a 4 nC beam of 30 psec pulse duration as it passes through a thin 2 cm Ar plasma lens. We are also developing a negative R_56 compressor beamline that will allow us to create ramped sub-picosecond beams of a shape well suited for driving large amplitude plasma wake fields and producing high transformer ratios. Simulations made using the 2-1/2 dimensional particle-in-cell code MAGIC indicate that we could use these ramped beams to produce fields of up to 10 GeV/m in a 10(16) cm(-3) plasma. Ramped beams are also suitable for driving plasma density gradient trapping experiments. When such a beam passes through a region where the plasma density drops suddenly the fast variation of the wake fields traps several pC of plasma electrons in the accelerating portion of the wake field. |
| title: | Chicane compressor development for BNL ATF- applications to SASE FEL |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | R. Agustsson,J. Rosenzweig |
| abstract: | A chicane compressor is being designed and constructed at UCLA for implementation at the BNL Accelerator Test Facility. The beam optics, including collective fields, and expected performance of the device has been simulated using TRACE3D and ELEGANT. Based on these studies, as well as constraints due to downstream ATF optics, the chicane magnet specifications were determined. The dipole magnets were designed using AMPERES 3D magnetostatic modeling, and have been constructed. Implementation of this device at the ATF, as well as initial physics experiments on coherent synchrotron radiation emission (and associated emittance growth) at 70 MeV, and expected performance enhancement of the VISA SASE FEL experiment, are discussed. |
| title: | Chirped-beam two-stage SASE-FEL for high power femtosecond X-ray pulse generation |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | . |
| abstract: | We present a method for generating femtosecond duration X-ray pulses using a single-pass free-electron laser (FEL). This method uses an energy-chirped electron beam to produce a frequency-chirped X-ray pulse through self-amplified spontaneous emission (SASE). After the undulator we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse, and therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped-beam two-stage SASE-FEL, and consider the performance of the chirped-beam two-stage option for the for the Linac Coherent Light Source (LCLS). |
| title: | Chirped-beam two-stage SASE-FEL for high power femtosecond x-ray pulse generation |
| conference: | Conference on Optics for Fourth-Generation X-Ray Sources |
| year: | 2001 |
| authors: | C. Schroeder,C. Pellegrini,S. Reiche,J. Arthur,P. Emma |
| abstract: | We present a method for generating femtosecond duration x-ray pulses using a single-pass free-electron laser (FEL). This method uses an energy-chirped electron beam to produce a frequency-chirped x-ray pulse through self-amplified spontaneous emission (SASE). After the undulator we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse, and therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped-beam two-stage SASE-FEL, and consider the performance of the chirped-beam two-stage option for the Linac Coherent Light Source (LCLS). |
| title: | Commissioning and measurements of the Neptune photo-injector |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | S. Anderson,M. Loh,P. Musumeci,J. Rosenzweig,H. Suk,M. Thompson |
| abstract: | The photo-injector for the Neptune Advanced Accelerator Laboratory is introduced. Its component parts, including the radio frequency gun, photo-cathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics, and control system are described. The injector is designed to produce high brightness, short pulse electron beams. Measurements of the photo-injector beams including quantum efficiency, emittance, pulse length, and pulse compression are presented. (21 References). |
| title: | Commissioning of the Neptune photoinjector |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | R. Agustsson,J. Rosenzweig,S. Anderson,P. Musumeci,M. Loh,M. Thompson,S. Boucher,A. Burke,J. England |
| abstract: | The status of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The components of the photoinjector: the RF gun and booster linac, chicane compressor, and beam diagnostic systems are described. Measurement techniques used to diagnose the short pulse length, high brightness beam are detailed and measurements of emittance and pulse compression are given. The effect of the pulse compressor on transverse emittance is explored. (11 References). |
| title: | Commissioning of the UCLA PEGASUS Photoinjector Laboratory |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | S. Telfer,S. Reiche,J. Rosenzweig,P. Frigola,G. Andonian |
| abstract: | The PEGASUS Photoinjector has been commissioned at UCLA. The Plane Wave Transformer Photoinjector provides a high-brightness 17 MeV beam that will be used for numerous beam-radiation studies. Some of these will include SASE FEL, transition radiation from non-standard surfaces, and monochromatic x-ray production via PXR and Thompson scattering. |
| title: | Design considerations for a SASE X-ray FEL |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | C. Pellegrini |
| abstract: | The well developed theory of short wavelength SASE-FELs is now being used to design two X-ray lasers, LCLS and Tesla-FEL. However, the physics and technology of these projects present some unique challenges, related to the very high peak current of the electron beam, the very long undulator needed to reach saturation, and the importance of preserving the beam phase-space density even in the presence of large wake-field effects. In the first part of the paper, we review the basic elements of the theory, the scaling laws for an X-ray SASE-FEL, and the status of the experimental verification of the theory. We then discuss some of the most important issues for the design of these systems, including wake-field effects in the undulator, and the choice of undulator type and beam parameters. (74 References). |
| title: | Development of an X-Band PWT Photoinjector |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | D. Newsham,Y. Luo,J. Zeng,D. Yu,J. Rosenzweig |
| abstract: | Development of an X-band Plane-Wave-Transformer (PWT), integrated photoinjector continues. Modifications of the end-cell design in this two-section device allow for simultaneous frequency and phase tuning of the accelerating field, thus preventing deceleration at the drift region that separates the two sections. The Los Alamos version of PARMELA is used to determine the expected performance parameters from the final design. |
| title: | Dynamics of a Driver Beam Propagating in an Underdense Plasma with a Downward Density Transition |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | H. Suk,N. Barov,J. England,E. Esarey,G. Kim,J. Rosenzweig,M. Thompson |
| abstract: | When a short electron beam propagates in an underdense plasma (plasma density n_p < beam density n_b) with a downward density transition, it is known that some background plasma electrons are trapped and accelerated by the plasma wakefield[1]. Beam quality of the trapped plasma electrons is severely affected by the wakefield that is generated by the driving electron beam, so dynamics and instabilities of the driver beam are very important. In this paper, we present some simulation results on the self-trapping and driver beam dynamics. |
| title: | Emittance measurements of the space charge dominated Thomson source photoinjector |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | S. Anderson,J. Rosenzweig,G. Le Sage,J. Crane |
| abstract: | The photocathode rf gun test facility in Livermore National Laboratory's Thomson source is described. The quadrupole scan and slit based emittance measurement techniques are used to measure the emittance of the space charge dominated beam. Experimental results are compared with simulation and theoretical calculations. (10 References). |
| title: | Exponential gain and saturation of a self-amplified spontaneous emission free-electron laser |
| journal: | Science |
| vol-pages: | 2037-41 |
| year: | 2001 |
| authors: | S. Milton,E. Gluskin,N. Arnold,C. Benson,W. Berg,S. Biedron,M. Borland,Y. Chae,R. Dejus,M. Den Hartog,B. Deriy,M. Erdmann,Y. Eidelman,M. Hahne,Z. Huang,K. Kim,J. Lewellen,Y. Li,A. Lumpkin,O. Makarov,E. Moog,A. Nassiri,V. Sajaev,R. Soliday,B. Tieman,E. Trakhtenberg,G. Travish,I. Vasserman,G. Wiemerslage,B. Yang,N. Vinokurov,X. Wang |
| abstract: | Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent X-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational X-ray free-electron laser. (30 References). |
| title: | IFEL experiment at the Neptune Lab |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | P. Musumeci,C. Pellegrini |
| abstract: | We present a two stage Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Lab. Proof-of-principle experiments on the IFEL scheme have been carried out successfully. This experiment is intended to achieve a 100 MeV energy gain, staging two IFEL modules. It will use a 16 MeV electron beam, a 1 TW CO/sub 2/ laser and two different tapered helical undulators. The problem of refocusing both laser and electron beam is analyzed in detail. A preliminary beam-line layout and numerical simulation are presented. (11 References). |
| title: | Initial gain measurements of an 800 nm SASE FEL, VISA |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | P. Frigola,A. Murokh,P. Musumeci,C. Pellegrini,S. Reiche,J. Rosenzweig,A. Tremaine,M. Babzien,I. Ben-Zvi,E. Johnson,R. Malone,G. Rakowsky,J. Skaritka,X. Wang,K. Van Bibber,L. Bertolini,J. Hill,G. Le Sage,M. Libkind,A. Toor,R. Carr,M. Cornacchia,L. Klaisner,H. Nuhn,R. Ruland,D. Nguyen |
| abstract: | The visible to infrared SASE amplifier (VISA) FEL is designed to obtain high gain at a radiation wavelength of 800 nm. The FEL uses the high brightness electron beam of the accelerator test facility (ATF), with energy of 72 MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6 mm and a period of 1.8 cm. To obtain large gain the beam and undulator axis have to be aligned to better than 5 mu m. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations. (10 References). |
| title: | Intra-undulator measurements at VISA FEL |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | A. Murokh,P. Frigola,C. Pellegrini,J. Rosenzweig,A. Tremaine,E. Johnson,X. Wang,V. Yakimenko,L. Klaisner,H. Nuhn,A. Toor |
| abstract: | We describe a diagnostics system developed, to measure exponential gain properties and the electron beam dynamics inside the strong focusing 4-m long undulator for the VISA (Visible to Infrared SASE Amplifier) FEL. The technical challenges included working inside the small undulator gap, optimising the electron beam diagnostics in the high background environment of the spontaneous undulator radiation, multiplexing and transporting the photon beam. Initial results are discussed. |
| title: | Investigations of electron-beam microbunching and beam coalignment using CTR in a high-gain SASE FEL |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | A. Lumpkin,W. Berg,S. Biedron,M. Borland,Y. Chae,R. Dejus,J. Lewellen,S. Milton,E. Moog,G. Travish,B. Yang |
| abstract: | We recently extended our experiments on z-dependent electron-beam microbunching using coherent transition radiation (CTR) into the high-gain, self-amplified spontaneous emission free-electron laser (FEL) regime. The UV-visible FEL at the Advanced Photon Source was operated at 530 nm and 385 nm using the bunch-compressed photocathode gun electron beam, linac, and 21.6 m of undulator length. The longitudinal microbunching of the electron beam was tracked by inserting a metal foil and a mirror after each of the nine 2.4-m-long undulators. The visible CTR generated by the electron-beam interaction was imaged and analyzed for z-dependent intensity, angular distribution, and spot size. Additionally, the image centroids and structures were used in evaluating the critical electron beam/photon beam overlap issue as a complement to the trajectory data from the beam position monitors. (9 References). |
| title: | Limitations on Measuring a Transverse Profile of Ultradense Electron Beams with Scintillators |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | A. Murokh,J. Rosenzweig,I. Ben-Zvi,X. Wang,V. Yakimenko |
| abstract: | As the high-brightness electron beams become denser and reach sub-100 um sizes, a resolution of the transverse profile diagnostics become an important issue. The applicability of the traditional scintillators as the diagnostics for most generic transverse properties of small dense beams is questionable. Recently, a YAG:Ce single crystal was used successfully, but studies indicated the presence of saturation effects. At BNL-ATF (Accelerator Test Facility) we have generated ultra-small beams, and continued an experimental work to further illuminate the nature of YAG:Ce saturation. We have also evaluated alternative diagnostics, such as LuAG:Ce. Imaging properties of various diagnostics were studied, including measurements of emission spectra. |
| title: | Measuring FEL radiation properties at VISA-FEL |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | A. Murokh,R. Agustsson,P. Frigola,C. Pellegrini,S. Reiche,J. Rosenzweig,A. Tremaine,M. Babzien,I. Ben-Zvi,E. Johnson,R. Malone,G. Rakowsky,J. Skaritka,X. Wang,K. Van Bibber,L. Bertolini,J. Hill,G. Le Sage,M. Libkind,A. Toor,R. Carr,M. Cornacchia,L. Klaisner,H. Nuhn,R. Ruland |
| abstract: | The VISA (Visible to Infrared SASE Amplifier) SASE free electron laser has been successfully operated at the Accelerator Test Facility (ATF) at BNL. High gain and saturation were observed at 840 nm. We describe here the diagnostic system, experimental procedures and data reduction algorithms, as the FEL performance was measured along the length of the undulator. We also discuss selected spectral radiation measurements. (10 References). |
| title: | Monitoring and manipulation of sub-picosecond beams |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | J. Rosenzweig |
| abstract: | In cutting-edge applications such as advanced accelerators and free-electron lasers, very high brightness beams of duration shorter than a picosecond are required. Further, these applications demand specific types of longitudinal beam profiles, such as pulse trains, and ramped pulses. The production of such types of beams present challenges both in technique, and in the instrumentation required to verify the method employed. The techniques for producing such short beams which have received the most investigation in recent years include chicane compression, and modulation via free-electron laser mechanism and its inverse. We discuss the principles and relevant single particle and collective effects which impact their performance. We review progress in implementing these schemes, as well as newer concepts such as relativistic velocity bunching and use of negative R_56 compressors. We also discussed the challenges in diagnosing these state-of-the-art beam systems. |
| title: | ORION: An Advanced Accelerator Facility at SLAC |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | D. Palmer,E. Colby,M. Hogan,R. Noble,R. Siemann,J. Spencer,D. Walz,C. Joshi,W. Mori,J. Rosenzweig,T. Katsouleas,P. Muggli,R. Byer |
| abstract: | Extending the center-of-mass energy frontier for high-energy physics depends on the research and development that is conducted now in the area of advanced accelerator physics and technology. In this article, we present the design and beam dynamics simulations for the emittance-compensated, RF photoinjector of the ORION Facility. (4 References). |
| title: | On the IFEL experiment at the UCLA Neptune Lab |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | P. Musumeci,C. Pellegrini,J. Rosenzweig,A. Varfolomeev,S. Tolmachev,T. Yarovoi |
| abstract: | We present an inverse free electron laser accelerator proposed for construction at the UCLA Neptune Lab. This experiment will use a 1TW CO/sub 2/ laser to accelerate through two strongly tapered undulators an electron beam from 16 MeV up to 55 MeV. The scheme proposed is the diffraction dominated IFEL interaction. The Raleigh range of the laser beam is about 2 cm, much shorter than the interaction length (the undulator length is 50 cm). In this regime adiabatic capture is possible in the first part of the undulator. In the focus region, we propose a solution to the problem of the dephasing between electrons and photons due to the Guoy phase shift. Ponderomotive effects and implications for tolerances are also studied. (13 References). |
| title: | Optimization of an X-ray SASE FEL |
| conference: | 19th ICFA Beam Dynamics Workshop on Physics of, and Science with, the X-Ray Free-Electron Laser |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | C. Pellegrini,S. Reiche,J. Rosenzweig,C. Schroeder,A. Varfolomeev,S. Tolmachev,H. Nuhn |
| abstract: | The most important characteristics of an X-ray SASE-FEL are determined by the electron beam energy, transverse and longitudinal emittance, and by choice of the undulator period, field, and gap. Among them are the gain and saturation length, the amount and spectral characteristics of the spontaneous radiation, the wake fields due to the vacuum pipe. The spontaneous radiation intensity is very large in all X-ray SASE-FELs now being designed, and it contributes to the final electron beam energy spread, thus affecting the gain. It also produces a large background for the beam and radiation diagnostics instrumentation. The wake fields due to the resistivity and roughness of the beam pipe through the undulator, also affects the beam 6-dimensional phase space volume, and thus the gain and the line width. In this paper, we discuss ways to optimize the FEL when considering all these effects. In particular we consider and discuss the use of a hybrid iron-permanent magnet helical undulator to minimize some of these effects, and thus optimize the FEL design. |
| title: | Optimization of an x-ray SASE-FEL |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | C. Pellegrini,S. Reiche,J. Rosenzweig,C. Schroeder,A. Varfolomeev,S. Tolmachev,H. Nuhn |
| abstract: | The most important characteristics of an X-ray SASE-FEL are determined by the electron beam energy, transverse and longitudinal emittance, and by choice of the undulator period, field, and gap. Among them are the gain and saturation length, the amount and spectral characteristics of the spontaneous radiation, the wake fields due to the vacuum pipe. The spontaneous radiation intensity is very large in all X-ray SASE-FELs now being designed, and it contributes to the final electron beam energy spread, thus affecting the gain. It also produces a large background for the beam and radiation diagnostics instrumentation. The wake fields due to the resistivity and roughness of the beam pipe through the undulator, also affects the beam 6-dimensional phase space volume, and thus the gain and the line width. In this paper, we discuss ways to optimize the FEL when considering all these effects. In particular we consider and discuss the use of a hybrid iron-permanent magnet helical undulator to minimize some of these effects, and thus optimize the FEL design. |
| title: | Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition |
| journal: | Physical Review Letters |
| vol-pages: | 1011?1014 |
| year: | 2001 |
| authors: | J. Rosenzweig,E. Esarey |
| abstract: | A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a single, short electron pulse travels through an underdense plasma with a sharp, localized, downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field, due to the rapid wavelength increase of the induced wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell simulations. To investigate the trapping and acceleration mechanisms further, a 1D Hamiltonian analysis, as well as 1D simulations, has been performed, with the results presented and compared. |
| title: | Production and synchronization of electron beams from RF photoinjector/compressor systems for ultra-fast applications |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | M. Thompson,J. Rosenzweig |
| abstract: | The RF photoinjector, when coupled with a magnetic pulse compression system, is now an ubiquitous tool for production of sub-picosecond electron beam pulses which are to be used in advanced accelerator and light source experiments. As the time-scale for both pulse lengths and synchronization to external systems approaches the femtosecond level, a clear understanding of the longitudinal dynamics of the electron injector is required. This paper presents an analysis of the longitudinal beam dynamics of electron bunches in the photoinjector/compressor system from birth at the photocathode, through their initial violent acceleration in the RF gun, and subsequent phase space manipulation in the post-acceleration linac and magnetic chicane. The phenomena of phase focusing due to RF forces, and defocusing due to longitudinal space-charge, are discussed, as is the process of magnetic pulse compression. The issues relevant to synchronization of electron pulses with external lasers are examined, using the examples of beat-wave acceleration and Compton light sources, and solutions involving appropriate compressor configurations are proposed. Diagnosis of the relevant physical effects in such schemes is discussed. |
| title: | Proposal for a IR Waveguide SASE FEL at the PEGASUS Injector |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | S. Reiche,J. Rosenzweig,S. Telfer |
| abstract: | Free Electron Lasers up to the visible regime are dominated by diffraction effects, resulting in a radiation size much larger than the electron beam. Thus the effective field amplitude at the location of the electron beam, driving the FEL process, is reduced. By using a waveguide, the radiation field is confined within a smaller aperture and an enhancement of the FEL performance can be expected. The PEGASUS injector at UCLA will be capable to provide the brilliance needed for an IR SASE FEL. The experiment PERSEUS (Power Enhanced Radiation Source Experiment Using Structures) is proposed to study the physics of a waveguide SASE FEL in a quasi 1D environment, where diffraction effects are strongly reduced as it is the case only for future FELs operating in the VUV and X-ray regime. The expected FEL performance is given by this presentation. |
| title: | Proposal for a IR waveguide SASE FEL at the PEGASUS injector |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | S. Reiche,J. Rosenzweig,S. Telfer |
| abstract: | Free Electron Lasers up to the visible regime are dominated by diffraction effects, resulting in a radiation size much larger than the electron beam. Thus the effective field amplitude at the location of the electron beam, driving the FEL process, is reduced. By using a waveguide, the radiation field is confined within a smaller aperture and an enhancement of the FEL performance can be expected. The PEGASUS injector at UCLA will be capable to provide the brilliance needed for an IR SASE FEL. The experiment Power Enhanced Radiation Source Experiment Using Structures (PERSEUS) is proposed to study the physics of a waveguide SASE FEL in a quasi I D environment, where diffraction effects are strongly reduced as it is the case only for future FELs operating in the VUV and X-ray regime. The expected FEL performance is given by this presentation. |
| title: | Quantum effects in high-gain free-electron lasers |
| journal: | Physical Review E |
| vol-pages: | 056502 |
| year: | 2001 |
| authors: | C. Schroeder,C. Pellegrini,P. Chen |
| abstract: | A many-particle fully quantized theory for a free-electron laser which is valid in the high-gain regime is presented. We examine quantum corrections for the high-gain single-pass free-electron laser. It is shown that quantum effects become significant when the photon energy becomes comparable to the gain bandwidth. The initiation of the free-electron laser process from quantum fluctuations in the position and momentum of the electrons is considered, and the parameter regime for enhanced start-up is identified. Photon statistics of the free-electron laser radiation are discussed, and the photon number statistics for the self-amplified spontaneous emission are calculated. (21 References). |
| title: | RF photoinjector development for a short-pulse, hard X-ray Thomson scattering source |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | G. Le Sage,S. Anderson,T. Cowan,J. Crane,T. Ditmire,J. Rosenzweig |
| abstract: | An important motivation in the development of the next generation X-ray light sources is to achieve picosecond and sub-ps pulses of hard X-rays for dynamic studies of a variety of physical, chemical anti biological processes. Present hard X-ray sources are either pulse-width or intensity limited, which allows ps-scale temporal resolution only for signal averaging of highly repetitive processes. A much faster and brighter hard X-ray source is being developed at LLNL, based on Thomson scattering of fs-laser pulses by a relativistic electron beam, which will enable X-ray characterization of the transient structure of a sample in a single shot. Experimental and diagnostic techniques relevant to the development of next generation sources including the Linac Coherent Light Source can be tested with the Thomson scattering hard X-ray source. This source will combine an RF photoinjector with a 100 MeV S-band linac. The photoinjector and linac also provide an ideal test-bed for examining space-charge induced emittance growth effects. A program of beam dynamics and diagnostic experiments are planned in parallel with Thomson source development. Our experimental progress and future plans will be discussed. |
| title: | Saturation measurements of a visible SASE FEL |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | A. Tremaine,P. Frigola,A. Murokh,C. Pellegrini,S. Reiche,J. Rosenzweig,M. Babzien,I. Ben-Zvi,E. Johnson,R. Malone,G. Rakowsky,J. Skaritka,X. Wang,V. Yakimenko |
| abstract: | VISA (visible to infrared SASE amplifier) is an FEL designed to obtain high gain at a radiation wavelength of 800 nm. Large gain is achieved by driving the FEL with the 71 MeV, high brightness beam of the Accelerator Test Facility (ATF) and using a novel, strong focusing, 4 m long undulator with a gap of 6 mm and a period of 1.8 cm. We report measurements of exponential gain, saturation, and spectra of the FEL radiation intensity. (11 References). |
| title: | Start-to-end simulation for the LCLS X-ray FEL |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | S. Reiche,C. Pellegrini,J. Rosenzweig,P. Emma,P. Krejcik |
| abstract: | X-ray FELs, such as the LCLS and TESLA FEL, require electron beams with large peak current and very small emittance. The X-ray peak power, temporal and spectral properties, depend significantly on details of the electron beam phase space distribution. The electron beam distribution is determined by many effects, as the emission process at the gun photo-cathode, bunch compression, acceleration and wakefields within the undulator. Although analytical results can give an estimate of the expected performance, the complexity of the electron beam generation, acceleration and compression can only be evaluated using a numerical simulation of all these processes, a start-to-end simulation. In this presentation we discuss the LCLS X-Ray FEL performance estimated by a start-to-end simulation, and we compare the results with those obtained using a simpler model. (19 References). |
| title: | The PEGASUS free electron laser laboratory |
| conference: | 22nd International Free Electron Laser Conference |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | S. Telfer,S. Reiche,J. Rosenzweig,P. Frigola |
| abstract: | The PEGASUS (Photoelectron Generated Amplified Spontaneous Radiation Source) free electron laser laboratory is currently being commissioned at UCLA. |
| title: | The free-electron laser collective instability and the development of X-ray FELs |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | C. Pellegrini |
| abstract: | We discuss the physics of collective instabilities in particle beams, and consider one particular case: the free-electron laser (FEL) collective instability. We present a review of the main characteristics of this instability, and its application to the development of Self Amplified Spontaneous Emission (SASE) FELs from the infrared to the X-ray region. (17 References). |
| title: | Transition radiation for uneven, limited surfaces |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | S. Reiche,J. Rosenzweig |
| abstract: | In the most common approach to modeling transition radiation, the annihilation of the incident particle with its image particle at the metallic boundary is calculated. This is valid only for ideal planar boundaries, and is not applicable if the surface is modulated, rough or limited in the transverse dimension. In this paper, we show results obtained by replacing the image current with the induced surface charge and surface distributions. Special problems such as a modulated surface are analytically solved and compared to a numerical simulation. Implications for experimental use of transition radiation-based beam monitors are discussed. (9 References). |
| title: | Trapping of background plasma electrons in a beam-driven plasma wake field using a downward density transition |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year published: | 2001 |
| year authored: | 2000 |
| authors: | H. Suk,N. Barov,J. Rosenzweig,E. Esarey |
| abstract: | Trapping of background plasma electrons by a beam-driven plasma wake field is studied as a new self-injection method. In this scheme, a short electron beam pulse is sent through an underdense plasma with a downward density transition and some background plasma electrons are trapped by the strong wake field due to the sudden increase of the wake wave wavelength at the density transition. Two-dimensional PIC (Particle-In-Cell) simulations show that a significant amount of plasma electrons are trapped and accelerated to a higher energy than the driving beam energy. Furthermore, the trapped-beam quality is fairly good. In this paper, the 2-D simulation results, dynamics of the trapped beam and the driving beam, and the proposed experiment for the UCLA Neptune Laboratory are described. (15 References). |
| title: | Ultra high-gradient energy loss by a pulsed electron beam in a plasma |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| authors: | N. Barov,K. Bishofberger,J. Rosenzweig,J. Carneiro,P. Colestock,H. Edwards,M. Fitch,W. Hartung,J. Santucci |
| abstract: | The plasma wake-field mechanism can be used to couple energy at a high rate from a bunched electron beam into a plasma wave. We will present results from the Fermilab A0 facility where a beam with an initial energy of 14 MeV passes through the plasma to emerge with a much broader energy spread, spanning from a low of 3 MeV to a high of over 20 MeV. Over the 8 cm length of the 10(14) cm(-3) plasma, this implies a 140 MeV/m deceleration and 72 MeV/m acceleration gradient. (12 References). |
| title: | Visible-infrared self-amplified spontaneous emission amplifier free electron laser undulator |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 122402 |
| year: | 2001 |
| authors: | R. Carr,M. Cornacchia,P. Emma,H. Nuhn,B. Poling,R. Ruland,E. Johnson,G. Rakowsky,J. Skaritka,S. Lidia,P. Duffy,M. Libkind,P. Frigola,A. Murokh,C. Pellegrini,J. Rosenzweig,A. Tremaine |
| abstract: | The visible-infrared self-amplified spontaneous emission amplifier (VISA) free electron laser (FEL) is an experimental device designed to show self-amplified spontaneous emission (SASE) to saturation in the near infrared to visible light energy range. It generates a resonant wavelength output from 800?600 nm, so that silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is designed to show how SASE FEL theory corresponds with experiment in this wavelength range, using an electron beam with emittance close to that planned for the future Linear Coherent Light Source at SLAC. VISA comprises a 4 m pure permanent magnet undulator with four 99 cm segments, each of 55 periods, 18 mm long. The undulator has distributed focusing built into it, to reduce the average beta function of the 70?85 MeV electron beam to about 30 cm. There are four FODO cells per segment. The permanent magnet focusing lattice consists of blocks mounted on either side of the electron beam, in the undulator gap. The most important undulator error parameter for a free electron laser is the trajectory walk-off, or lack of overlap of the photon and electron beams. Using pulsed wire magnet measurements and magnet shimming, we were able to control trajectory walk-off to less than ±50 µm per field gain length. |
| title: | A diagnostic system to measure SASE-FEL radiation properties along the 4-meter VISA undulator |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | A. Murokh,E. Johnson,J. Rosenzweig,A. Tremaine |
| abstract: |
| title: | A method for measuring the FEL radiation power along an undulator |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | S. Reiche |
| abstract: | A highly desirable measurement in Free Electron Laser (FEL) experiments is the dependency of the radiation power along the undulator. Most designs of undulators prohibit detection of the radiation power within the undulator or extracting the electron beam at arbitrary positions. Transport of both, the radiation field and the electron beam, through the entire undulator, and thus an ongoing FEL interaction, is unavoidable. If there are many correction magnets distributed along the beam pipe, one can think of exciting a large orbit distortion downstream from any of these correctors. For a gain length comparable to or larger than the beta function this excitation of a coherent betatron oscillation might degrade the FEL amplification to a level, for which the radiation power does not further grow over the remaining length of the undulator. This paper presents the efficiency of this method for the parameters of the VUV FEL at the TESLA Test Facility. |
| title: | A two stage IFEL accelerator |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | P. Musumeci,C. Pellegrini |
| abstract: | We present a two stage Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Lab. Proof-of-principle experiments on the IFEL scheme have been carried out succesfully. This experiment is intended to achieve a 100 Mev energy gain, staging two IFEL modules. It will use the 16 Mev electron beam produced by the Neptune linac, the 1 TW MARS CO2 laser and two different tapered undulators. The problem of refocusing both laser and electron beam is analyzed in detail. A preliminary beamline layout and numerical simulations are presented. |
| title: | Boiling the Vacuum with an X-ray FEL |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | C. Pellegrini |
| abstract: | We discuss the possibility of producing an electromagnetic field on the order of the Schwinger critical field by focusing the X-ray beam produced by the X-ray free-electron laser, LCLS, under development by a SLAC-ANL-BNL-LANL-UCLA collaboration. We also discuss an experiment which would use this very large field to test QED through the production of electron-positron pairs in vacuum, with no real particles being present in the initial state. |
| title: | Characterizing The Electron Beam For The Aps Leutl Free Electron Laser |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | G. Travish,J. Lewellen,M. Hahne |
| abstract: | The Advanced Photon Source (APS) Low-Energy Undulator Test Line (LEUTL) project was originally intended to test and characterize advanced undulator designs via electron beambased diagnostics technique. It is presently being used to conduct free electron laser (FEL) research for a future fourth-generation light source. The APS injector linac has been upgraded to deliver a beam suitable for these FEL tests. The project has as an initial goal the operation of a self amplified spontaneous emission (SASE) device operating in the visible at 530 nm (green light). The visible FEL requires a 217 MeV moderately high brightness beam with a peak current of 100 A or greater, a normalized rms emittance of 5 ?m or less, and an energy spread of 0.1% or better. Beam characterization is fundamental to being able to match experimental results with theoretical models. This paper describes the LEUTL FEL, lists the major goals, the beam diagnostics, and presents the initial electron beam measured properties. Future plans are also discussed. |
| title: | Commissioning of the Neptune Photoinjector |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | S. Anderson,J. Rosenzweig,A. Burke,X. Ding,M. Loh,P. Musumeci,C. Pellegrini,H. Suk,M. Thompson,C. Clayton,C. Joshi,K. Marsh,P. Muggli |
| abstract: | The status of the commissioning of the rf photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the rf gun, photocathode drive laser system, booster linac, rf system, chicane compressor, beam diagnostics systems, and control system are described. Recent improvements in the rf gun, rf timing, and chicane compressor systems are detailed. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented. |
| title: | Compensation of FEL gain reduction by emittance effects in a strong focusing lattice |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | S. Reiche |
| abstract: | As the constraint of a small transverse emittance becomes more severe, the higher the electron beam energy in an FEL. To compensate for the transverse and thus the longitudinal velocity spread. a compensation scheme has been proposed previously by Derbenev and Sessler et al., for Free Electron Lasers by introducing a correlation between the energy and the average betatron amplitude of each electron. This compensation scheme is based on a constant absolute value of the transverse velocity, a feature of the natural focusing of undulators. and does not include strong focusing of a superimposed quadrupole lattice. This paper focuses on the electron motion in a strong focusing lattice with a variation in the axial velocity. The resulting reduction of the compensation efficiency is analyzed using simulations. It is seen that the compensation scheme is not much affected if the lattice cell length is shorter than the gain length. For the results presented in this paper, the parameters of the proposed TESLA X-ray FEL have been used. |
| title: | Electron Beam Photocathode Cleaning |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | M. Thompson,S. Anderson,M. Loh,P. Musumeci,J. Rosenzweig,H. Suk,D. Palmer |
| abstract: | We are experimenting with low energy electron beams as a means of cleaning and improving the quantum efficiency of metallic photocathodes. Electron beam surface cleaning has been used successfully in electron cooling devices at Fermilab (S. Nagaitsev) and Novosibirsk (A.N. Sharapa and A.V. Shemyakin). The cooling device data indicates that a 2 mA h/cm2 specific dose of 3 keV electrons on the surface of the photocathode will produce a surface with an outgas rate at least one order of magnitude lower than a 24 hour 400° C bake achieves. We are currently commissioning a photocathode cleaning "mini-gun" based on a 1 cm2 dispenser cathode to determine how these reduced outgassing rates translate into improvements in quantum efficiency. The mini-gun will be permanently attached to a spare laser port on our 1.6 cell photoinjector gun so that we can clean in situ and on the fly. The cleaning beam will have a large spot size (~5mm) and ample current up to 60 mA at 5 keV. We expect cleaning times on the order of several minutes to achieve a 2 mA h/cm2 specific dose over the interaction region of the photocathode. |
| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma |
| format: | preprint |
| year: | 2000 |
| authors: | N. Barov,J. Rosenzweig,M. Thompson |
| abstract: | There has been much interest in the regime of plasma wake-field acceleration (PWFA) having ultra-high fields, and associated nonlinear plasma motion. With an exact analytical approach, we examine here a fundamental limit of PWFA excitation, by an infinitesimally short relativistic bunched beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams. |
| title: | HOMDYN study for the LCLS RF photo-injector |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | M. Ferrario,J. Clendenin,D. Palmer,J. Rosenzweig,L. Serafini |
| abstract: | We report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that led to the discovery of a new effective working point for a split RF photoinjector. The HOMDYN code, the main simulation tool adopted in this work, is described together with its recent improvements. The new working point and its LCLS application is discussed. Validation tests of the HOMDYN model and low emittance predictions, 0.3 mm-mrad for a 1 nC flat top bunch, are performed with respect to the multi-particle tracking codes ITACA and PARMELA. (26 References). |
| title: | High power femtosecond pulses from an X-ray SASE-FEL |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | C. Pellegrini |
| abstract: | We discuss how to use the large-gain bandwidth of an X-ray SASE-FEL to produce femtosecond long pulses by chirping and compressing the output FEL radiation. We consider the power level, spectral width, and intensity fluctuations of the compressed X-ray pulse compared to the case with no compression. (9 References). |
| title: | High-Brightness Beam Generation and Characterization at the Advanced Photon Source Low-Energy Undulator Test Line Linac |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | J. Lewellen,S. Biedron,M. Borland,M. Hahne,K. Harkay,A. Lumpkin,S. Milton,N. Sereno,G. Travish |
| abstract: | Improvements to the Advanced Photon Source injector linac have been made to allow for the production and characterization of high-brightness beams in support of fourth-generation light source research. In particular, effort has been directed at generating beams suitable for use in the low-energy undulator test line (LEUTL) free-electron laser (FEL). We describe the enhancements to the linac operational and diagnostic capabilities that enabled self-amplified spontaneous emission (SASE) operation of the FEL at 530 nm. Electron beam measurement techniques and recent results will be discussed. Beam properties are measured under the same operational conditions as those used for FEL studies. The nominal FEL beam parameters are as follows: 217 MeV beam energy; less than 0.15 mm-mrad normalized emittance; 100 A peak current from a 0.7-nC charge at a 7-psec bunch. |
| title: | High-Brightness Beams from a Light Source Injector: The Advanced Photon Source Low-Energy Undulator Test Line Linac |
| conference: | 2000 Linear Accelerator Conference |
| year: | 2000 |
| authors: | G. Travish,S. Biedron,M. Borland,M. Hahne,K. Harkay,J. Lewellen,A. Lumpkin,S. Milton,N. Sereno |
| abstract: | The use of existing linacs, and in particular light source injectors, for free-electron laser (FEL) experiments is becoming more common due to the desire to test FELs at ever shorter wavelengths. The high-brightness, highcurrent beams required by high gain FELs impose technical specifications that most existing linacs were not designed to meet. Moreover, the need for specialized diagnostics, especially shot-to-shot data acquisition, demands substantial modification and upgrade of conventional linacs. Improvements have been made to the Advanced Photon Source (APS) injector linac in order to produce and characterize high brightness beams. Specifically, effort has been directed at generating beams suitable for use in the low-energy undulator test line (LEUTL) FEL in support of fourth-generation light source research. The enhancements to the linac technical and diagnostic capabilities that allowed for self-amplified spontaneous emission (SASE) operation of the FEL at 530 nm are described. Recent results, including details on technical systems improvements and electron beam measurement techniques, will be discussed. The linac is capable of accelerating beams to over 650 MeV. The nominal FEL beam parameters used are as follows: 217 MeV energy; 0.1-0.2% rms energy spread; 4-8 um normalized rms emittance; 80-120 A peak current from a 0.2-0.7 nC charge at a 2-7 ps FWHM bunch. |
| title: | Highlights of AAC 2000 Workshop |
| conference: | 2000 Linear Accelerator Conference |
| year: | 2000 |
| authors: | J. Rosenzweig |
| abstract: | The Advanced Accelerator Concepts 2000 (AAC2K) Workshop was held in Santa Fe in June, 2000, and included a wide array of conceptual and theoretical advances at the frontier of accelerator physics. This paper reviews the highlights of the workshop, with subjects ranging from acceleration using lasers, plasmas and microstructures, to the beam physics of muon colliders. Particular emphasis is given to the topics which are relevant to research at existing linear accelerator facilities, and the effect of this research on the capabilities of such facilities. |
| title: | IFEL experiment at Neptune Lab |
| conference: | 2000 European Particle Accelerator Conference |
| year: | 2000 |
| authors: | P. Musumeci,C. Pellegrini |
| abstract: | We present a two stage Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Lab. Proof-of-principle experiments on the IFEL scheme have been carried out successfully. This experiment is intended to achieve a 100 MeV energy gain, staging two IFEL modules. It will use a 16 MeV electron beam, a 1 TW CO2 laser and two different tapered helical undulators. The problem of refocusing both laser and electron beam is analysed in detail. A preliminary beam-line layout and numerical simulations are presented. |
| title: | Initial operation of S-band plane wave transformer photoinjector |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | X. Ding,C. Pellegrini,J. Rosenzweig,S. Telfer |
| abstract: | An integrated S-Band RF photoinjector based on the plane wave transformer (PWT) is being built and operated in the Particle Beam Physics Laboratory at UCLA. This novel structure integrates a photocathode directly into a PWT Linac making the structure simple and compact. Due to the strong coupling between each adjacent cell, this structure is relatively easy to fabricate and operate. This photoinjector can provide high brightness beams at energies of 15 to 20MeV, with emittance less than 1mm-mrad at charge of 1 nC. These short-pulse beams can be used in various applications: space charge dominated beam physics studies, plasma lenses, plasma accelerators, free-electron laser microbunching techniques, and SASE-FEL physics studies. It will also provide commercial opportunities in chemistry, biology and medicine. The initial operation of the PWT photoinjector with high RF power is described. A comparation of experimental result and theoretical design is also discussed. |
| title: | Limitations on the resolution of YAG:Ce beam profile monitor for high brightness electron beam |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | A. Murokh,J. Rosenzweig,V. Yakimenko,E. Johnson,X. Wang |
| abstract: | The performance of single crystal YAG:Ce (Y_(3)Al_(5)O_(12)) beam profile monitors was studied for transverse masurements on the high brightness ultrarelativistic electron beam at Accelerator Test Facility (ATF) at BNL. The test demonstrated systematic intensity dependent beam enlargement on YAG monitors, compared to other diagnostics. Possible mechanisms of the effect have been studied. The quantitative examination was performed and compared to the developed phenomenological models. Limitations on the use of YAG:Ce diagnostics are discussed with respect to the high-brightness electron sources. |
| title: | Multi-dimensional free-electron laser simulation codes: a comparison study |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | S. Biedron,Y. Chae,R. Dejus,B. Faatz,H. Freund,S. Milton,H. Nuhn,S. Reiche |
| abstract: | A self-amplified spontaneous emission (SASE) free-electron laser(FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL. |
| title: | New design study and related experimental program for the LCLS RF photoinjector |
| conference: | 2000 European Particle Accelerator Conference |
| year: | 2000 |
| authors: | M. Ferrario,P. Bolton,J. Clendenin,D. Dowell,S. Gierman,M. Hernandez,D. Nguyen,D. Palmer,J. Rosenzweig,J. Schmerge,L. Serafini |
| abstract: | We report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that lead to the discovery of a new effective working point for a split RF photoinjector. We consider the emittance compensation regime of a space charge beam: by increasing the solenoid strength, the emittance evolution shows a double minimum behavior in the drifting region. If the booster is located where the relative emittance maximum and the envelope waist occur, the second emittance minimum can be shifted to the booster exit and frozen at a very low level (0.3 mm-mrad for a 1 nC flat top bunch), to the extent that the invariant envelope matching conditions are satisfied. Standing Wave Structures or alternatively Traveling Wave Structures embedded in a Long Solenoid are both candidates as booster linac. A careful measurement of the emittance evolution as a function of position in the drifting region is necessary to verify the computation and to determine experimentally the proper position of the booster cavities. The new design study and supporting experimental program under way at the SLAC Gun Test Facility are discussed. |
| title: | Non-equilibrium transverse motion and emittance growth in space-charge dominated beams |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | S. Anderson,J. Rosenzweig |
| abstract: | The transverse dynamics of space-charge dominated beams are investigated both analyitically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave-breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined, in order to illuminate the most effective approaches to beam handling during the emittance compensation process, as well as during subsequent beam transport. |
| title: | Nonequilibrium transverse motion and emittance growth in space-charge dominated beams |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | S. Anderson,J. Rosenzweig |
| abstract: | The transverse dynamics of space-charge dominated beams are investigated both analytically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave-breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined, in order to illuminate the most effective approaches to beam handling during the emittance compensation process, as well as during subsequent beam transport. (13 References). |
| title: | Nonequilibrium transverse motion and emittance growth in ultrarelativistic space-charge dominated beams |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 094201 |
| year: | 2000 |
| authors: | S. Anderson,J. Rosenzweig |
| abstract: | The transverse dynamics of space-charge dominated beams are investigated both analytically and computationally, in order to understand the mechanisms for emittance oscillations and growth due to nonlinear space-charge fields. This work explores the role of space-charge dominated equilibrium and its relationship to phase space wave breaking, which is responsible for the irreversible emittance growth in these systems. The physics of both coasting and accelerating beams are examined in order to illuminate the most effective approaches to beam handling during the emittance compensation process as well as during subsequent beam transport. These results are discussed within the context of recent ultrahigh brightness RF photoinjector designs. (20 References). |
| title: | Observation of plasma wakefield acceleration in the underdense regime |
| journal: | Physical Review Special Topics-Accelerators & Beams |
| vol-pages: | 011301 |
| year: | 2000 |
| authors: | N. Barov,J. Rosenzweig,M. Conde,W. Gai,J. Power |
| abstract: | Initial experiments which have explored the physics of the underdense (blowout) regime of the plasma wakefield accelerator (PWFA) at the Argonne Wakefield Accelerator facility are reported. In this regime, the relativistic electron beam is denser than the plasma, causing the beam channel to completely rarefy, and leaving a high quality accelerating region which also contains a uniform ion column. This ion column in turn allows the drive and accelerating beams to be well guided over many initial beam beta-function lengths. The results of these experiments, which have taken place over several years, are reviewed. Notable achievements in the course of these studies include the creation and measurement of drive and witness beam generated in an rf photoinjector, as well as previously published studies on drive beam guiding in the underdense regime. In addition, these experiments allowed measurement of both beam energy loss and gain, at a maximum average rate of 25 MeV/m in this regime of the PWFA, which is consistent with a peak acceleration gradient of 62 MeV/m in the excited waves. Difficulties associated with this type of experiment are discussed, as are prospects for mitigating these difficulties and achieving high gradient acceleration in planned future experiments. |
| title: | Observation of self-amplified spontaneous emission and exponential growth at 530 nm |
| journal: | Physical Review Letters |
| vol-pages: | 988-91 |
| year: | 2000 |
| authors: | S. Milton,E. Gluskin,S. Biedron,R. Dejus,P. Den Hartog,J. Galayda,K. Kim,J. Lewellen,E. Moog,V. Sajaev,N. Sereno,G. Travish,N. Vinokurov,N. Arnold,C. Benson,W. Berg,J. Biggs,M. Borland,J. Carwardine,Y. Chae,G. Decker,B. Deriy,M. Erdmann,H. Friedsam,C. Gold,A. Grelick,M. Hahne,K. Harkay,Z. Huang,E. Lessner,R. Lill,A. Lumpkin,O. Makarov,G. Markovich,D. Meyer,A. Nassiri,J. Noonan,S. Pasky,G. Pile,T. Smith,R. Soliday,B. Tieman,E. Trakhtenberg,G. Trento,I. Vasserman,D. Walters,X. Wang,G. Wiemerslage,S. Xu,B. Yang |
| abstract: | Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator. (20 References). |
| title: | Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition |
| format: | preprint |
| year: | 2000 |
| authors: | H. Suk,N. Barov,J. Rosenzweig,J. Rosenzweig,E. Esarey |
| abstract: | A new scheme for plasma electron injection into an acceleration phase of a plasma wakefield is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp, localized downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell (PIC) simulations. To investigate the trapping and acceleration mechanism further, a 1-D Hamiltonian analysis as well as 1-D simulations have been performed, with the results are presented and compared. |
| title: | Plasma electron trapping and acceleration in a plasma wake field using a density transition |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | H. Suk,N. Barov,J. Rosenzweig,E. Esarey |
| abstract: | A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp downward density transition and some plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave at the density transition. To investigate the trapping and acceleration mechanism, two-dimensional particle-in-cell (PIC) simulations were performed, and the illustrative 2-D simulation shows that the new injection method can produce a relatively large charge (~0.5 nC), short (~1 ps) and high energy (> driving beam energy) electron beam pulse with a plasma density transition from 5x10(13) cm(-3) to 3.5x10(13) cm(-3). In addition to the 2-D simulations, 1-D analytic work based on the Hamiltonian formalism and 1D simulations have been performed and the results are also presented. Finally, a proposed experiment at the Neptune Laboratory of UCLA is described. |
| title: | Plasma source test and simulation results for the underdense plasma lens experiment at the UCLA Neptune Laboratory |
| journal: | IEEE Transactions on Plasma Science |
| vol-pages: | 271-7 |
| year: | 2000 |
| authors: | H. Suk,C. Clayton,C. Joshi,T. Katsouleas,P. Muggli,R. Narang,C. Pellegrini,J. Rosenzweig |
| abstract: | The planned plasma lens experiment at the UCLA Neptune Laboratory is described. In the experiment, electron beams with an energy of 16 MeV, a charge of 4 nC, and a pulse duration of 30 ps full-width at half-maximum (FWHM) are designed to be produced from the 1.625-cell photoinjector radio-frequency gun (f=2.856 GHz) and PWT linac in the Neptune. The generated beams are passed through a thin plasma with a density of low 10/sup 12/ cm/sup -3/ range and a thickness of a few centimeters. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. In this paper, the overview of the planned plasma lens experiment and the test results of the plasma source for various conditions are presented. In addition, computer simulations with a 2-1/2 dimensional particle-in-cell code (MAGIC) were performed and the simulation results are shown. (19 References). |
| title: | Radiation pulse line-width and time duration control for an X-ray free-electron laser. |
| conference: | APS April Meeting |
| year: | 2000 |
| authors: | C. Pellegrini |
| abstract: | An X-ray free-electron laser, named the Linear Coherent Light Source (LCLS), will be built at SLAC using the SLAC linear accelerator. LCLS is being developed by a SLAC-ANL-BNL-LANL-UCLA collaboration. The LCLS will produce coherent radiation at 1.5 to 0.15 nm, with peak power as high as 10 GW in a 100fs pulse length, and a line width of about 0.01possibilities now being studied to manipulate the X-ray pulse to control the peak power between 1 and 10 GW, the line-width between 0.01between 100 and 10 fs. |
| title: | Report of the U.S. Department of Energy Fusion Energy Sciences Advisory Committee (FESAC) panel reviewing the theory and computing program |
| journal: | Journal of Fusion Energy |
| vol-pages: | 229-44 |
| year: | 2000 |
| authors: | J. Sheffield,T. Antonsen,L. Berry,M. Brown,J. Dahlburg,R. Davidson,M. Greenwald,C. Hegna,W. McCurdy,D. Newman,C. Pellegrini,C. Phillips,D. Post,M. Rosenbluth,T. Simonen,J. Van Dam |
| abstract: | This Panel was set up by the Fusion Energy Sciences Advisory Committee (FESAC) at its November 2000 meeting for the purpose of addressing questions from the Department of Energy concerning the theory and computing/simulation program of the Office of Fusion Energy Sciences. Although the Panel primarily addressed programmatic questions, it acknowledges that the theory and computing in fusion energy sciences has a stellar record of research successes. (A recent FESAC report entitled "Opportunities in the Fusion Energy Sciences Program" listed a number of theory and computing research highlights.) Last year the National Research Council performed an assessment of the quality of the fusion energy sciences program-including theory and computing-and concluded that the quality of its research is on a par with that of other leading areas of contemporary physical science. |
| title: | Simulation of time-dependent energy modulation by wake fields and its impact on gain in the VUV free electron laser of the TESLA Test Facility |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | S. Reiche,H. Schlarb |
| abstract: | For shorter bunches and narrower undulator gaps the interaction between the electrons in the bunch and the wake fields becomes so large that the FEL amplification is affected. For a typical vacuum chamber of an X-ray or VUV Free Electron Laser three major sources of wake fields exist: a resistance of the beam pipe, a change in the geometric aperture and the surface roughness of the beam pipe. The generated wake fields, which move along with the electrons, change the electron energy and momentum, depending on the electron longitudinal and transverse position. In particular, the accumulated energy modulation shifts the electrons away from the resonance condition. Based on an analytic model the energy loss by the wake fields has been incorporated into the time-dependent FEL simulation code GENESIS 1.3. For the parameters of the TESLA Test Facility the influence of the bunch length, beam pipe diameter and surface roughness has been studied. The results are presented in this paper. |
| title: | Single crystal copper photo-cathode in the BNL/SLAC/UCLA 1.6 cell RF gun |
| conference: | 2nd ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | D. Palmer,S. Anderson,J. Rosenzweig |
| abstract: | Previous experimental measurements in the two dimensional (2D) variation of the quantum efficiency, QE, of a polycrystalline copper photo-cathode have measured a 25% variation in this quantity. Two possible causes of this 2D QE variation are contamination of the photo-emitting surface and the work function variation of copper due to crystal facet orientation. We report on the progress to eliminate the 2D QE variation due to the non-uniform crystal facet orientation of copper photo-emitters. This is accomplished by replacing the polycrystalline photo-emitter region of the cathode plane in a modified version of the BNL/SLAC/UCLA 1.6 cell rf gun with a thin disk of a single crystal copper Cu_100. In this paper we present a theoretical discussion on the effect that the crystal structure orientation of a photo-emitter has on the 2D QE. The manufacturing process used in the construction of the single crystal Cu_100 photo-cathode used in these photo-emission experiments are discussed. Preliminary experimental results are presented along with a discussion of our future experimental plans. |
| title: | Status and initial commissioning of a high gain 800 nm SASE FEL |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | A. Tremaine,P. Frigola,A. Murokh,P. Musumeci,C. Pellegrini,J. Rosenzweig,M. Babzien,I. Ben-Zvi,E. Johnson,R. Malone,G. Rakowsky,J. Skaritka,X. Wang,L. Yu,K. Van Bibber,J. Hill,G. Le Sage,R. Carr,M. Cornacchia,H. Nuhn,R. Ruland,D. Nguyen |
| abstract: | We describe the status and initial commissioning of the visible to infrared SASE amplifier (VISA) experiment. VISA uses a strong focusing 4 m undulator, the Brookhaven National Laboratory ATF linac with an energy of 72 MeV, and a photoinjector electron source. The VISA fundamental radiation wavelength is near 800 nm and the power expected at saturation is near 60 MW. Power, angular and spectral measurements are planned for the VISA radiation and these results will be analyzed and compared with SASE FEL theory and computer simulation. In addition, the induced electron beam micro-bunching will be measured using coherent transition radiation. (12 References). |
| title: | The Drive Laser for the APS LEUTL FEL RF Photoinjector |
| conference: | 21st International Free Electron Laser Conference |
| year published: | 2000 |
| year authored: | 1999 |
| authors: | G. Travish,N. Arnold,R. Koldenhoven |
| abstract: | The APS LEUTL free-electron laser (FEL) is a high-gain, short-wavelength device requiring a high-current, low-emittance beam. An rf photoinjector driven by a laser is used to provide the requisite beam. The drive laser consists of a diode-pumped Nd:Glass oscillator and a chirped pulse amplification (CPA) system consisting of a grating stretcher, a flashlamp-pumped Nd:Glass regenerative amplifier, and a grating compressor. The system generates 4-mJ pulses in the IR with a pulse length as short as 2 ps FWHM and a repetition rate of 6 Hz. Nonlinear doubling crystals are used to generate fourth-harmonic output of ~500 uJ in the UV (263 nm), which is required to exceed the work function of the copper cathode in the gun. This paper describes the drive laser as well as the extensive controls implemented to allow for remote operation and monitoring. Performance measurements as well as the operating experience are presented. |
| title: | A Comparison Between the Performance of Split and Integrated RF Photoinjectors |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | J. Rosenzweig,S. Anderson,X. Ding,L. Serafini |
| abstract: | RF photoinjectors, the present source of choice for production of ultra-high brightness electron beams, have two basic design types: split, in which a short, high gradient rf gun is followed by a a drift and a booster linac, and a lower gradient integrated photoinjector, in which the linac acceleration is connected directly to the gun. The first type is represented at UCLA by the Neptune photoinjector, the second by the newly constructed S-band PWT photoinjector. We examine, through simulation and theory, the relative merits of each type of injector, both from the point of view of the beam physics (ability of the source to produce high currents and low emittances), and of relative technical advantages. |
| title: | A High Voltage Extractor with Photocathodes |
| conference: | 1998 European Particle Accelerator Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | G. Travish,D. Giove,P. Michelato,C. Pagani,P. Pierini,L. Serafini,D. Sertore |
| abstract: | We describe a system designed for photocathode testing and beam dynamics studies which is based on a high voltage extractor and a sub–ps drive laser. The system’s distinctive characteristics are the ability to run in the short bunch regime — where the dynamics are not governed by the Child–Langmuir law — and the anticipated availability of both transverse and longitudinal beam diagnostics to determine the full beam distribution. The system consists of a pseudo parallel plate 100 kV DC gun with a removable cathode and a cathode–anode gap of 8 mm, yielding a cathode field of up to 10 MV/m. The drive laser is a Nd:Glass system capable of producing over 200 ?J at 264 nm with a pulse length adjustable from approximately 250 fs to over 1 ps. The goals of the system, described in this paper, are to support ongoing photocathode studies, including measuring high current density extraction from prepared cathodes and investigating the effect of surface variation of the quantum efficiency. Additional studies foreseen include parameterizing the effect of surface variations on the transverse emittance, and exploring beam dynamics such as the short bunch blow out regime which has recently been proposed as a way to produce uniform ellipsoidal charge density distributions[1]. |
| title: | A measurement of high gain SASE FEL induced electron beam micro-bunching using coherent transition radiation |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | A. Tremaine,S. Anderson,P. Frigola,M. Hogan,A. Murokh,C. Pellegrini,J. Rosenzweig,D. Nguyen,R. Sheffield |
| abstract: | Coherent transition radiation (CTR) was used to study the longitudinal modulations of an electron beam exiting the UCLA/LANL high gain SASE FEL. The induced longitudinal micro-bunching of the electron beam at the exit of the undulator was measured with a frequency domain technique using the CTR emitted when this beam strikes a thin conducting foil. Formalisms for both CTR and SASE theories are related using the simulation code GINGER in which the SASE FEL gain of the output radiation and the micro-bunching of the electron beam are given. Experimental results from the CTR measurement will show the limit of standard transition radiation theory is being approached and new analysis is needed. (8 References). |
| title: | A permanent-magnet focused X-band photoinjector |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | D. Yu,D. Newsham,P. Wilson,J. Zeng,J. Rosenzweig,X. Ding,F. Hartemann,E. Landahl |
| abstract: | A Plane-Wave-Transformer (PWT), integrated photoinjector operating at an X-band frequency (8.547GHz) is being developed by DULY Research Inc. in a DOE SBIR project, in collaboration with UCLA and UCD/ILSA. Upward frequency scaling from an S-band PWT photoinjector would result in a compact photoinjector with unprecedented brightness. Challenging technological innovations are required at X-band. In particular, water cooling capacity, mechanical support strength, and materials properties do not scale linearly with frequency. Instead of using large solenoids, we have successfully designed the required focusing for an X-band PWT using a compact, permanent magnet system. Also described in this paper is a system design of the X-band photoinjector, including the RF system and the cooling/support of the PWT structure. |
| title: | An Optimized Slab-Symmetric Dielectric-Based Laser Accelerator Structure |
| conference: | 8th Advanced Accelerator Concepts Workshop |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | J. Rosenzweig,P. Schoessow |
| abstract: | A slab-symmetric, partially dielectric filled, laser excited structure which may be used to accelerate charged particles is analyzed theoretically and computationally. The fields associated with the accelerating mode are calculated, as are aspects of the resonant filling and impedance matching of the structure to the exciting laser. It is shown through computer simulation that the accelerating mode in this structure can be excited resonantly and with large quality factor Q. Practical aspects of implementing this structure as an accelerator are discussed. (7 References). |
| title: | An X-ray transition radiation beam profile detector for the LCLS |
| conference: | 1998 ICFA Workshop on Nonlinear and Collective Phenomena in Beam Physics |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | S. Monteiro,C. Pellegrini |
| abstract: | We discuss the characteristics of a transverse beam profile detector for a high energy charged particle accelerator, and propose a candidate detector based on transition radiation in the X-ray region of the spectrum. The detector is useful for low emittance, high energy beams, for example, the LCLS electron beam. We expect that it can resolve spatial details as small as a few microns. The advantages of this method over previous ones are that the measurements are linear with the beam density and the results are a point by point map of the beam density. (14 References). |
| title: | Coherent Radiation Diagnosis of Self Amplified Spontaneous Emission free Electron Laser-Derived Electron beam Microbunching |
| format: | thesis |
| year: | 1999 |
| authors: | A. Tremaine |
| abstract: | This thesis presents an experiment in which the longitudinal profile of an electron beam was measured by studying the coherrent transition radiation (CTR) emitted when the beam strikes a thin conducting foil. A high gain Self Amplified Spontaneous Emission (SASE) Free Electron laser (FEL) was implemented and the source fo the longitudinal beam profile modulation. Diagnostics measuring very short periodic electron beam modulation will be necessary for future experiments in which the modulating wavelength will be several microns. Up to this point, there have been reliable tools used for such longitudinal beam profile measurements. However, the limits of resolution in these devices are being approached and new and less expensive methods are needed. Transition radiation from an electron beam striking a metallic surface is an easily emplementable and inexpensive diagnostic and is shown to be a reliable diagnostic for the future. This thesis presents the theoretical calculation of the expected CTR photon spectrums and compares the analysis with an experiment recently done on an electron beam which has been longitudinally modulated by SASE FEL. The accelerator beamline and its parameters important to the experiment are described. Also, discussed, are the requirements on the system needed for the best CTR emission possible and the importance in choosing a good metallic radiating foil. Results from the data are compared with computer simulation in which these issues are taken into account. Also, the experimental results point out approximations used in traditional transition radiation modeling that will not be valid in future CTR experiemnts and more rigorous theorectical analysis will be needed. |
| title: | Coherent transition radiation-based diagnosis of electron beam pulse shape |
| conference: | 8th Advanced Accelerator Concepts Workshop |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | J. Rosenzweig,A. Murokh,A. Tremaine |
| abstract: | The bunch shapes of an electron beams is increasingly difficult to measure, as the time-scales of interest are now sub-picosecond. We discuss here the use of coherent transition radiation (CTR) for such measurements. Two types of measurements are presented: the deduction of macroscopic (0.3 psec resolution) pulse profile using interferometry, and the examination of microbunch (50 fsec) structure from an FEL-bunched beam using spectral characteristics of the CTR. For the macrobunch measurement we discuss the problem of missing low frequency radiation and one solution for extracting meaningful data with this problem are presented. For microbunch CTR, we examining initial spectrally-resolved measurements, and some interesting deviations in the CTR spectrum from the standard theoretical predictions. (23 References). |
| title: | Commissioning of the Neptune photoinjector |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | S. Anderson,J. Rosenzweig,K. Bishofberger,X. Ding,T. Holden,A. Murokh,C. Pellegrini,H. Suk,A. Tremaine,C. Clayton,C. Joshi,K. Marsh,P. Muggli,R. Agustsson,S. Anderson,P. Musumeci,M. Loh,M. Thompson,S. Boucher,A. Burke,J. England |
| abstract: | The status of the commissioning of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the RF gun, photocathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics systems, and control system are described. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented. (10 References). |
| title: | Experimental non linear beam dynamics studies with a turn-by-turn phase space monitor at SPEAR |
| conference: | ICFA Workshop on Nonlinear and Collective Phenomena in Beam Physics |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | A. Terebilo,C. Pellegrini,M. Cornacchia |
| abstract: | About 10 years ago the possibility of using turn-by-turn phase beam position monitors to gain insight into phase space dynamics of a single particle in a storage ring raised some interest among accelerator physicists. It was soon argued that Landau damping and collective effects would seriously complicate the interpretation of data. We have established that in SPEAR it is possible to lock a single bunch into a collective 'rigid body' mode. When in this mode the bunch will behave similar to a super particle of finite size with the charge equal to that of the bunch. In this paper we report on experiments that demonstrate this effect. We also numerically study the strong coupling limit, in which the transition to 'rigid body' motion occurs, for the two models proposed earlier. We present the experiments on non-linear resonance crossing and frequency map measurement in the 'super particle' framework. (11 References). |
| title: | First results of the Fermilab high-brightness RF photoinjector |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | J. Carneiro,R. Carrigan,M. Champion,P. Colestock,H. Edwards,J. Fuerst,W. Hartung,K. Koepke,M. Kuchnir,J. Santucci,L. Spentzouris,M. Fitch,A. Melissinos,P. Michelato,C. Pagani,D. Sertore,N. Barov,J. Rosenzweig |
| abstract: | A collaboration has been formed between FNAL, UCLA, LNFN Milano, the University of Rochester, and DESY to develop the technology of an RF photoinjector, followed by a superconducting cavity, to produce high bunch charge (8 nC) with low normalized emittance ([left angle bracket]20 mm mrad) in bunch spacing trains of 800 bunches separated by mu s. The activities of bunch charge the collaboration fall into two categories: 1. the development of Injector II for the TeSLA/TTF accelerator. This photoinjector (TTF RF Gun) was tested at Fermilab in September and October 1998 and installed at DESY in November 1998. 2. the installation at the A0 Hall of Fermilab of a modified version of the TTF photoinjector, for photoinjector R&D and to study novel applications of high-brightness, pulsed electron beams. This photoinjector (A0 RF Gun) produced its first beam in March 1999. This paper presents a summary of the tests done at Fermilab on the TITF Injector II and the first results obtained on the new Fermilab photoinjector. |
| title: | GENESIS 1.3: a fully 3D time-dependent FEL simulation code |
| conference: | 20th International Free Electron Laser Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | S. Reiche |
| abstract: | Numerical simulation codes are basic tools for designing Free Electron Lasers (FEL). They are used to study the impact of different parameters, e.g. wiggler errors and external focusing, which allow FEL users to optimize the performance. For faster execution some simulation codes assume radial symmetry or decompose the radiation field into a few azimuthal modes, although then this treatment does not include the full description of the FEL. This contribution describes the new FEL code GENESIS 1.3 which uses a fully three-dimensional representation of the FEL equations in the paraxial approximation for time-dependent and steady-state simulations of single-pass FEL. In particular this approach is suitable for cases where the radial symmetry is broken by the electron beam distribution as well as by wiggler errors, betatron motion and off axis injection of the electron beam. The results, presented here, are based on the parameters of the TESLA Test Facility FEL at DESY. |
| title: | Influence of electron beam halos on the FEL performance |
| conference: | 20th International Free Electron Laser Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | B. Faatz,S. Reiche |
| abstract: | For single-pass free-electron lasers (FEL), such as amplifiers and SASE devices, saturation of the radiation power has to be reached within the length of the undulator. Therefore, detailed knowledge of electron beam parameters is crucial. So far, simulations have been performed with a given rms emittance and energy spread. At short radiation wavelengths, hunch compressors are used to compress the electron beam to achieve the desired high peak currents. In addition, external focusing along the entire undulator is used to maintain a constant small radius. The rotation of phase space due to compression might lead to a significant part of the bunch in tails that could increase the gain length. Furthermore, it is in general not possible to match both the beam core and the tail to the focusing structure. In this contribution, the influence of these tails, both transverse and in energy, on the FEL performance will be investigated. Simulations will be performed for beam parameters that have been assumed for the TESLA Test Facility FEL at DESY. |
| title: | Measured free-electron laser microbunching using coherent transition radiation |
| conference: | 20th International Free Electron Laser Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | A. Tremaine,J. Rosenzweig,S. Anderson,P. Frigola,M. Hogan,A. Murokh,C. Pellegrini,D. Nguyen,R. Sheffield |
| abstract: | The microbunch distribution of an electron beam exiting a SASE free-electron laser has been measured using the emitted coherent transition radiation (CTR) produced from a thin aluminum foil placed at the end of the undulator. The wavelength of the coherent transition radiation is shown to be the same as the FEL wavelength, and thus a measure of the beam microbunch spacing. Also, the study of the CTR linewidth and angular acceptance of the radiation captured are shown to be derived from this coherent radiative process. Scattering effects on the forward emitted transition radiation from the electron beam traversing an aluminum foil are also considered. (11 References). |
| title: | Numerical Studies for a Single Pass High Gain Free-Electron Laser |
| format: | thesis |
| year: | 1999 |
| authors: | S. Reiche |
| abstract: |
| title: | Optimal scaled photoinjector designs for FEL applications |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | J. Rosenzweig,S. Anderson,X. Ding,C. Pellegrini,G. Travish |
| abstract: | Much of the research and development surrounding the effort to create X-ray FELs based on the SASE process has centered on the creation of ultra-high brightness electron beam sources. The sources for existing short wavelength FEL designs, which employ RF photoinjector technology, have all been specified to contain 1 nC of charge. We show, by scaling existing designs, that this constraint causes the maximum beam brightness to be found when the RF wavelength is shortened to X-band. If, instead of holding the charge constant, we assume a certain RF wavelength device and then scale the charge, notable improvements in the beam brightness, and thus the FEL performance, are found. Charge scaling assumes that the density and aspect ratio of the beam stays constant as the charge is changed. If we relax the requirement of a constant aspect ratio in order to maximize the beam current and brightness by shortening the beam pulse, we find that the pulse lengthening due to space charge eventually brings this effort to a stop. The results of this investigation and their impact on SASE FEL design is discussed. |
| title: | Output power control in an X-ray FEL |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | C. Pellegrini,X. Ding,J. Rosenzweig |
| abstract: | Recent theoretical and experimental advances of the high gain self-amplified spontaneous emission free-electron laser (SASE-FEL), have demonstrated the feasibility of using this system as a 4/sup th/ generation light source. This source will produce diffraction-limited radiation in the 0.1 nm region of the spectrum, with peak power of tens of GW, subpicosecond pulse length, and very large brightness. The peak power density in such a system is very large, and in some experiments it might damage the optical systems or the samples, or it might be simply larger than what is needed for the particular experiment being considered. Some options to reduce the power level, for example by using a gas absorption cell to reduce the X-ray intensity, have been studied. In this paper we discuss another possibility to control the power output of an X-ray SASE-FEL by varying the charge from the electron source, and the longitudinal bunch compression during the acceleration in the linac. |
| title: | Photon beam diagnostics for VISA FEL |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | A. Murokh,C. Pellegrini,J. Rosenzweig,P. Frigola,P. Musumeci,A. Tremaine,M. Babzien,I. Ben-Zvi,A. Doyuran,E. Johnson,J. Skaritka,X. Wang,K. Van Bibber,J. Hill,G. Le Sage,D. Nguyen,M. Cornacchia |
| abstract: | The VISA (Visible to Infrared SASE Amplifier) project is designed to be a SASE-FEL driven to saturation in the sub-micron wavelength region. Its goal is to test various aspects of the existing theory of self-amplified spontaneous emission, as well as numerical codes. Measurements include: angular and spectral distribution of the FEL light at the exit and inside of the undulator; electron beam micro-bunching using CTR; single-shot time resolved measurements of the pulse profile, using an auto-correlation technique and FROG algorithm. The diagnostics are designed to provide maximum information on the physics of the SASE-FEL process, to ensure a close comparison of the experimental results with theory and simulations. (9 References). |
| title: | Slab symmetric dielectric micron scale structures for high gradient electron acceleration |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | P. Schoessow,J. Rosenzweig |
| abstract: | A class of planar microstructures is proposed which provide high accelerating gradients when excited by an infrared laser pulse. These structures consist of parallel dielectric slabs separated by a vacuum gap; the dielectric or the outer surface coating are spatially modulated at the laser wavelength along the beam direction so as to support a standing wave accelerating field. We have developed numerical and analytic models of the accelerating mode fields in the structure. We show an optimized coupling scheme such that this mode is excited resonantly with a large quality factor. The status of planned experiments on fabricating and measuring these planar structures is described. (9 References). |
| title: | Synchronization of sub-picosecond electron and laser pulses |
| conference: | 8th Advanced Accelerator Concepts Workshop |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | J. Rosenzweig,G. Le Sage |
| abstract: | Pulse-compression techniques apply a longitudinal restoring force which improves synchronization between electron bunches and the RF drive, partially or completely correcting errors in the exit time from the injector. While this feature is beneficial in terms of linac related phase matching issues and jitter in the photocathode laser system, laser jitter with respect to the RF clock is in fact worsened in terms of the final interaction of laser and electron pulses. That is, if one attempts to synchronize the electron bunch to an external laser, deriving external laser timing from, say, the photocathode drive laser oscillator, the relative timing of electron and the external laser will be mismatched, because the electron beam is pulled toward a given phase of the RF clock. Thus, if one wishes to take advantage of the locking of the electron beam to the (assumed stable) RF clock, then an equivalent mechanism must be found for locking the external laser to the RF clock as well. |
| title: | TREDI: fully 3D beam dynamics simulation of RF guns, bendings and FELs |
| journal: | Nuclear Instruments & Methods A |
| vol-pages: | 443-4 |
| year: | 1999 |
| authors: | L. Giannessi,P. Musumeci,M. Quattromini |
| abstract: | We describe a three-dimensional code modelling the propagation of charged beams in accelerator devices. The inclusion of space charge fields is taken into account by means of the Lienard-Wiechert retarded potentials. As an illustration of the capabilities of the program, the results of a simulation are given that, describe the beam dynamics from the cathode to the undulator through the whole accelerating system. Evidence of bunching in the undulator, as an indication of SASE is observed. |
| title: | Test results of the plasma source for underdense plasma lens experiments at the UCLA Neptune Lab |
| conference: | 8th Advanced Accelerator Concepts Workshop |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | H. Suk,C. Clayton,R. Narang,P. Muggli,J. Rosenzweig,C. Pellegrini,C. Joshi |
| abstract: | A plasma source was developed at UCLA for planned underdense plasma lens experiments, where the plasma density is less than the electron beam density. The argon plasma, produced by a discharge between a LaB_6 cathode at 1330 degrees C and a tantalum anode, is confined by a solenoidal magnetic field and flows transversely across the electron beam path. Extensive test of the plasma source is under way for various conditions before it is assembled with the UCLA photocathode-based electron linac. In particular, different longitudinal (with respect to the electron beam) plasma profiles and effective plasma lengths can be obtained by adjusting the moveable sliding door between the plasma source and the transverse beamline. Test results of the plasma source are presented. (11 References). |
| title: | The APS SASE FEL: Modeling and code comparison |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | S. Biedron,Y. Chae,R. Dejus,B. Faatz,H. Freund,S. Milton,H. Nuhn,S. Reiche |
| abstract: | A self-amplified spontaneous emission (SASE) free electron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL. |
| title: | The APS SASE FEL: status and commissioning results |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | S. Milton,S. Biedron,P. Den Hartog,J. Lewellen,E. Moog,A. Nassiri,G. Travish |
| abstract: | A self-amplified spontaneous emission (SASE) free-electron laser (FEL) is under construction at the Advanced Photon Source (APS). Three gun systems, an rf-test area, laser room, numerous diagnostics, a transfer line at the end of the linac and a new building, which will serve as the experimental hall, have been added. The only remaining items to be installed are the undulators into the beamline. Here, the additions to the APS in support of this project as well as commissioning results and future plans will be discussed. (9 References). |
| title: | The FEL development at the Advanced Photon Source |
| conference: | Free-Electron Laser Challenges II |
| year: | 1999 |
| authors: | S. Milton,N. Arnold,C. Benson,S. Berg,W. Berg,S. Biedron,Y. Chae,E. Crosbie,G. Decker,B. Deriy,R. Dejus,P. Hartog,R. Dortwegt,M. Erdmann,Z. Huang,H. Friedsam,H. Freund,J. Galayda,E. Gluskin,G. Goeppner,A. Grelick,J. Jones,Y. Kang,K. Kim,S. Kim,K. Kinoshita,R. Lill,J. Lewellen,A. Lumpkin,G. Markovich,O. Makarov,E. Moog,A. Nassiri,V. Ogurtsov,S. Pasky,J. Power,B. Tieman,E. Trakhtenberg,G. Travish,I. Vasserman,N. Vinokurov,D. Walters,J. Wang,X. Wang,B. Yang,S. Xu |
| abstract: | Construction of a single-pass free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) mode of operation is nearing completion at the Advanced Photon Source (APS) with initial experiments imminent. The APS SASE FEL is a proof-of-principle fourth-generation light source. As of January 1999 the undulator hall, end-station building, necessary transfer lines, electron and optical diagnostics, injectors, and initial undulators have been constructed and, with the exception of the undulators, installed. All preliminary code development and simulations have also been completed. The undulator hall is now ready to accept first beam for characterization of the output radiation. It is the project goal to push towards full FEL saturation, initially in the visible, but ultimately to UV and VUV, wavelengths. (10 References). |
| title: | The VISA FEL Undulator |
| conference: | 20th International Free Electron Laser Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | R. Carr,I. Ben-Zvi,L. Bertolini,M. Cornacchia,P. Emma,P. Frigola,E. Johnson,M. Libkind,S. Lidia,H. Nuhn,C. Pellegrini,G. Rakowsky,J. Rosenzweig,R. Ruland |
| abstract: | The Visible-Infrared SASE Amplifier (VISA) FEL is an experimental device designed to show self amplified spontaneous emission (SASE) to saturation in the 800-600 nm range, where silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is the first SASE FEL designed to saturate, and its diagnostics will provide important checks of theory. |
| title: | The design for the LCLS RF photoinjector |
| conference: | 20th International Free Electron Laser Conference |
| year published: | 1999 |
| year authored: | 1998 |
| authors: | R. Alley,V. Bharadwaj,J. Clendenin,P. Emma,A. Fisher,J. Frisch,T. Kotseroglou,R. Miller,D. Palmer,J. Schmerge,J. Sheppard,M. Woodley,A. Yeremian,J. Rosenzweig,D. Meyerhofer,L. Serafini |
| abstract: | We report on the design of the RF photoinjector of the Linac Coherent Light Source. The RF photoinjector is required to produce a single 150 MeV bunch of similar to 1 nC and similar to 100 A peak current at a repetition rate of 120 Hz with a normalized rms transverse emittance of similar to 1 pi mm-mrad. The design employs a 1.6-cell S-band RF gun with an optical spot size at the cathode of a radius of similar to 1 mm and a pulse duration with an rms sigma of similar to 3 ps. The peak RF field at the cathode is 150 MV/m with extraction 57 degrees ahead of the RF peak. A solenoidal field near the cathode allows the compensation of the initial emittance growth by the end of the injection linac. Spatial and temporal shaping of the laser pulse striking the cathode will reduce the compensated emittance even further. Also, to minimize the contribution of the thermal emittance from the cathode surface, while at the same time optimizing the quantum efficiency, the laser wavelength for a Cu cathode should be tunable around 260 nm. Following the injection linac the geometric emittance simply damps linearly with energy growth. PARMELA simulations show that this design will produce the desired normalized emittance, which is about a factor of two lower than has been achieved to date in other systems. In addition to low emittance, we also aim for laser amplitude stability of 1% in the UV and a timing jitter in the electron beam of 0.5 ps rms, which will lead to less than 10% beam intensity fluctuation after the electron bunch is compressed in the main linac. |
| title: | The development of S-band plane wave transformer photoinjector |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | X. Ding,C. Pellegrini,J. Rosenzweig,S. Telfer,A. Tremaine,W. Vernon,D. Yu,D. Newsham,J. Zeng,T. Lee,J. Chen |
| abstract: | An integrated S-band RF photoinjector based on the plane wave transformer (PWT) is being built in the Particle Beam Physics Laboratory at UCLA in collaboration with DULY Research. This novel structure integrates a photocathode directly into a PWT linac making the structure simple and compact. Due to the strong coupling between each adjacent cell, this structure is relatively easy to fabricate and operate. This photoinjector can provide high brightness beams at energies of 15 to 20 MeV, with emittance less than 1 mm-mrad at charge of 1 nC. These short-pulse beams can be used in various applications: space charge dominated beam physics studies, plasma lenses, plasma accelerators, free-electron laser microbunching techniques, and SASEFEL physics studies. It will also provide commercial opportunities in chemistry, biology and medicine. The present status of the PWT photoinjector including fabrication and cold test to characterise the structure is described. RF system and photocathode drive laser system are also discussed. |
| title: | The effects of RF asymmetries on photoinjection beam quality |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | J. Rosenzweig,S. Anderson,X. Ding,D. Yu |
| abstract: | A general multipole-based formalism to study the effects of RF asymmetries on the production of ultra-high brightness beam is presented, which employs both analytical and computational techniques. These field asymmetries can cause the degradation of beam emittance due to time dependent and nonlinear focusing effects. Two cases of interest are examined: the dipole asymmetry produced by a coupling slot in a standard high gradient RF gun, and the higher multipole content introduced by the support/cooling rods in a PWT structure. Practical implications of our results, as well as comparison to cold test and beam-based experimental tests, are discussed. (8 References). |
| title: | The operation of the BNL/ATF GUN-IV photocathode RF gun at the Advanced Photon Source |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| authors: | S. Biedron,G. Goeppner,J. Lewellen,S. Milton,A. Nassiri,G. Travish,X. Wang,N. Arnold,W. Berg,M. Babzien,C. Doose,R. Dortwegt,A. Grelick,J. Galayda,G. Markovich,S. Pasky,J. Power,B. Yang |
| abstract: | At the Advanced Photon Source (APS) at Argonne National Laboratory (ANL), a |