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137 papers
| title: | Generation and Measurement of Relativistic Electron Bunches Characterizzed by a Linearly Ramped Current Profile |
| format: | journal article |
| year: | May 28, 2008 |
| 3 authors: | | | |
| abstract: | We report the first successful attempt to generate ultrashort (1–10 ps) relativistic electron bunches characterized by a ramped longitudinal current profile that rises linearly from head to tail and then falls sharply to zero. Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free-electron lasers as a means of reducing asymmetry in microbunching due to slippage. The scheme used to generate the ramped bunches employs an aniso-chronous dogleg beam line with nonlinear correction elements to compress a beam having an initial positive time-energy chirp. The beam current profile is measured using a deflecting mode cavity, and a pseudoreconstruction of the beam’s longitudinal phase space distribution is obtained by using this diagnostic with a residual horizontal dispersion after the dogleg. |
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| title: | Breakdown Limits on Gigavolt-per-Meter Electron-Beam-Driven Wakefields in Dielectric Structures |
| format: | journal article |
| year: | May 27, 2008 |
| 15 authors: | | | | | | | | | | | | | | | |
| abstract: | First measurements of the breakdown threshold in a dielectric subjected to GV=m wakefields produced by short (30 – 330 fs), 28.5 GeV electron bunches have been made. Fused silica tubes of 100 |
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| title: | Dielectric Wakefield Accelerator Experiments at the Saber Facility |
| format: | conference procceeding |
| conference: | PAC07 |
| year: | 2007 |
| 17 authors: | | | | | | | | | | | | | | | | | |
| abstract: | Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC Final Focus Test Beam (FFTB), are foreseen to be produced at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of multi-GV/m in plasmas. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 um and 200 um ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in fused silica (with full data analysis still ongoing) [1]. With the construction and commissioning of the SABER facility at SLAC, new experiments would be made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. This collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures. |
| keywords: | pbpl |
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| title: | Experiment to Measure Ramped Electron Bunches at the UCLA Neptune Laboratory Using a Transverse Deflecting Cavity |
| format: | conference procceeding |
| conference: | 12th Advanced Accelerator Concepts Workshop |
| year: | 2006 |
| 5 authors: | | | | | |
| 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. |
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| title: | Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation |
| format: | conference procceeding |
| conference: | |
| year: | |
| 8 authors: | | | | | | | | |
| abstract: | We discuss future experimental work proposed to study the performance of a cylindrical dielectric wakefield accelerating structure as a coherent Cerenkov radiation source at the Neptune laboratory at UCLA. The Cerenkov wakefield acceleration experiment carried out recently by UCLA/SLAC/USC, using the ultrashort and high charge beam (Q = 3 nC, RMS bunch length = 20 micron) at the SLAC FFTB, demonstrated electromagnetic wakes at the few GV/m level. The motivation of our prospective experiment is to investigate the operation of a similar scenario using the comparatively long pulse, low charge beam (Q = 0.5 nC, RMS bunch length = 200 micron) at UCLA Neptune. The field amplitude produced in this setup would be one to two orders of magnitude lower, at the few tens to few 100 MV/m level. Such a decelerating field would extract a significant amount of energy from a low-energy beam in a distance on the order of a few centimeters, allowing the use of short dielectric structures. We discuss details of the geometry and composition of the structures to be used in the experiment. We also examine the possibility of a future dedicated facility at UCLA Neptune based on a hybrid photoinjector currently in development. The intrinsic bunch compression capabilities and improved beam parameters (RMS bunch length = 100 micron, Q = 1 nC) of the photoinjector would allow the creation of a high power radiation source in the terahertz regime. |
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| title: | PRELIMINARY RESULTS FROM THE UCLA/SLAC ULTRA-HIGH GRADIENT CERENKOV WAKEFIELD ACCELERATOR EXPERIMENT |
| format: | conference procceeding |
| conference: | Erice 2005 |
| year: | 2006 |
| 12 authors: | | | | | | | | | | | | |
| 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. |
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| title: | RESULTS FROM THE UCLA/FNPL UNDERDENSE PLASMA LENS EXPERIMENT |
| format: | conference procceeding |
| conference: | Erice 2005 |
| year: | 2006 |
| 11 authors: | | | | | | | | | | | |
| 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 σx,y ≈ 650 μm and σz ≈ 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 also imaged into a streak camera in order to directly measure the correlation between z and σ within the beam. |
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| title: | The LCLS Single-shot Relative Bunch Length Monitor System |
| format: | conference procceeding |
| conference: | Erice 2005 |
| year: | 2006 |
| 4 authors: | | | | |
| abstract: | The Particle Beam Physics Lab (PBPL) at UCLA is developing a single-shot relative bunch length monitor system for the Linac Coherent Light Source (LCLS) X-ray Free Electron Laser at SLAC. To ensure high-quality lasing, feedback systems are needed. The bunch length monitor system will be a crucial part of the linac longitudinal feedback system, which is necessary to keep the final peak beam current stable. The system will consist of two multi-channel single-shot grating polychromators, one after each bunch compressor, and will use the coherent synchrotron radiation (CSR) or coherent edge radiation (CER) from bunch compressor chicane dipole magnets. Details of the system will be presented, and the system will be compared to alternatives. Plans for testing and integration into the LCLS beamline will be presented as well. |
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| title: | Working Group 2 Summary: Diagnostics and Beam Manipulation |
| format: | talk |
| year: | 2005 |
| 1 author: | |
| 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. |
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| title: | Creation of plasma density transitions short compared to the plasma skin-depth |
| format: | journal article |
| year: | 2005 |
| 3 authors: | | | |
| 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 |
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| title: | High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| 17 authors: | | | | | | | | | | | | | | | | | |
| 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 ¯eld 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 ¯rst 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. |
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| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| 19 authors: | | | | | | | | | | | | | | | | | | | |
| 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. |
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| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| format: | preprint |
| year: | 2005 |
| 19 authors: | | | | | | | | | | | | | | | | | | | |
| 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. |
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| title: | Observation of Anomalously Large Spectral Bandwidth in a High Gain Self-amplified Spontaneous Emission Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| 14 authors: | | | | | | | | | | | | | | |
| 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. |
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| title: | RF AND MAGNETIC MEASUREMENTS ON THE SPARC PHOTOINJECTOR AND SOLENOID AT UCLA |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| 8 authors: | | | | | | | | |
| 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. |
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| title: | Velocity bunching of high-brightness electron beams |
| format: | journal article |
| year: | 2005 |
| 11 authors: | | | | | | | | | | | |
| 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. |
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| title: | Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| 11 authors: | | | | | | | | | | | |
| 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. |
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| title: | Observation of Anomalously Large Spectral Bandwidth in a High-Gain Self-Amplified Spontaneous Emission Free Elctron Laser |
| format: | journal article |
| year: | 2005 |
| 14 authors: | | | | | | | | | | | | | | |
| 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. |
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| title: | X-Band Dipole Mode Deflecting Cavity for the UCLA Neptune Beamline |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| 5 authors: | | | | | |
| 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. |
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| title: | Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system |
| format: | journal article |
| year: | 2005 |
| 9 authors: | | | | | | | | | |
| 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. |
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| title: | A Coherent Compton Backscattering High Gain FEL Using an X-Band Microwave Undulator |
| format: | conference procceeding |
| conference: | Proceedings of the 27th International Free Electron Laser Conference |
| year: | 2005 |
| 6 authors: | | | | | | |
| abstract: | High power microwave sources at X-Band, delivering 400 to 500 of megawatts for about 400 ns, have been recently developed. These sources can power a microwave undulator with short period and large gap, and can be used in short wavelength FELs reaching the nm region at a beam energy of about 1 GeV. We present here an experiment designed to demonstrate that microwave undulators have the field quality needed for high gain FELs. compensate RF power losses, it might be convenient to have an open waveguide geometry, as will be discussed later in the paper. However the initial FEL calculations are based on a circular cross-section waveguide. The undulator is powered by two transverse electric modes, shifted in the time phase by |
| keywords: | pbpl |
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| title: | Sextupole Correction of the Longitudinal Transport of Relativistic Beams in Dispersionless Translating Sections |
| format: | journal article |
| year: | |
| 6 authors: | | | | | | |
| abstract: | We examine the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg. Through heuristic analytical arguments and examples derived from recent experimental endeavors and augmented by simulations using the particle tracking codes PARMELA and ELEGANT, sextupole corrections are found to be potentially useful in facilitating the use of such structures for beam compression or for shaping the current profile of the beam, by manipulation of the second-order longitudinal dispersion (or T566). Recent experimental evidence of the use of sextupoles to manipulate second-order horizontal and longitudinal dispersion of the beam is presented. The theoretical and experimental results indicate that these manipulations could be used to create an electron bunch with a current profile having a long ramp followed by a sharp cut-off, which is optimal for driving large amplitude wake fields in a plasma wake field accelerator. |
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| title: | Optimization and beam dynamics of a superconducting radio-frequency gu |
| format: | journal article |
| year: | |
| 5 authors: | | | | | |
| abstract: | Recent advances in superconducting radio-frequency (RF) technology and a better understanding of RF photoinjector design optimization make it possible to propose a specific design for a superconducting RF gun that can simultaneously produce both ultra-high peak brightness and high average current. Such a device is a critical component of next generation X-ray sources, such as self-amplified spontaneous emission free-electron lasers (SASE FEL) and energy recovery linac-based systems. The design presented in this paper is scaled from the present state-of-the-art normal conducting RF photoinjector that has been studied in the context of the linac coherent light source and SPARC SASE FEL injection schemes. Issues specific to the superconducing RF photoinjector, such as accelerating gradient limit, RF cavity and cryostat design, and compatibility with magnetic focusing and laser excitation of a photocathode are discussed. |
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| title: | Ultra-High Density Electron Beams for Beam Radiation and Beam Plasma Interaction |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | |
| 11 authors: | | | | | | | | | | | |
| abstract: | Current and future applications of high brightness electron beams, which include advanced accelerators such as the plasma wake-field accelerator (PWFA) and beam radiation interactions such as inverse-Compton scattering (ICS), require both transverse and longitudinal beam sizes on the order of tens of microns. Ultra-high density beams may be produced at moderate energy (50 MeV) by compression and subsequent strong focusing of low emittance, photoinjector sources. We describe the implementation of this method used at the PLEIADES ICS x-ray source in which the photoinjector-generated beam has been compressed to 300 fsec duration using the velocity bunching technique and focused to 20 um rms size using an extremely high gradient, permanent magnet quadrupole (PMQ) focusing system. |
| keywords: | pbpl |
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| title: | Status of the UCLA/NICADD Plasma Density Transition Trapping Experiment |
| format: | preprint |
| year: | 2004 |
| 8 authors: | | | | | | | | |
| 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. |
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| title: | Creation of plasma density transitions short compared to the plasma skin depth |
| format: | preprint |
| year: | 2004 |
| 3 authors: | | | |
| 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. |
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| title: | A PMQ-based, Ultra-short Focal Length, Final Focus System for Next Generation Beam-Radiation and Beam-Plasma Experiments |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 4 authors: | | | | |
| 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. |
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| title: | A PMQ-based, Ultra-short Focal Length, Final Focus System for Next Generation Beam-Radiation and Beam-Plasma Experiments |
| format: | talk |
| year: | 2004 |
| 1 author: | |
| 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. |
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| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 7 authors: | | | | | | | |
| abstract: | The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, σz= 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 few 100 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. |
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| title: | A Helical Undulator Wave-guide Inverse Free-Electron Laser |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 8 authors: | | | | | | | | |
| 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. |
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| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 7 authors: | | | | | | | |
| 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. |
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| title: | VISA IB: Ultra-High Bandwidth, High Gain SASE FEL |
| format: | journal article |
| year: | |
| 15 authors: | | | | | | | | | | | | | | | |
| abstract: | We report the results of a high energy spread SASE FEL experiment, the intermediary experiment linking the VISA I and VISA II projects. A highly chirped beam (1.7 %) was transported, without corrections of longitudinal aberrations in the ATF dogleg, and injected into the VISA undulator. The ouput radiation displayed an uncharacteristicly large bandwidth (12 %) with extremely stable lasing and mea- sured energy of about 2 μJ . Start-to-end simulations re- produced key features of the experiment and provided an insight into the michanisms giving rise to such a high band- width. These analyses have important implications on the VISA II experiment. |
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| title: | Free-Electron Lasers as Pumps for High-Energy Solid-State Lasers |
| format: | conference procceeding |
| conference: | 25th International Free Electron Laser Conference |
| year: | 2004 |
| 3 authors: | | | |
| 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. |
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| title: | Design Considerations for a High-Efficiency High-Gain Free-Electron Laser for Power Beaming |
| format: | conference procceeding |
| conference: | 25th International Free Electron Laser Conference |
| year: | 2003 |
| 2 authors: | | |
| 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. |
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| title: | Design and Status of the VISA II Experiment |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 12 authors: | | | | | | | | | | | | |
| 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. |
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| title: | Status of the Inverse Free Electron Laser Experiment at the Neptune Laboratory |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 10 authors: | | | | | | | | | | |
| 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. |
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