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S.G. Anderson

First Name: Scott

Middle Name: G.

Last Name: Anderson

Full Name: S.G. Anderson

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pbpl  alumni  phd

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45 papers
 title: Commissioning of a High-Brightness Photoinjector for Compton Scattering X-Ray Sources format: conference proceeding conference: PAC 2007 year: 2007 13 authors: | | | | | | | | | | | | abstract: Compton scattering of intense laser pulses with ultra- relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV ener- gies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free- electron lasers and laser and plasma based advanced accel- erators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scatter- ing experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emit- tance diagnostic development, results of sputtered magne- sium photo-cathode experiments, and UV laser pulse shap- ing are discussed. Initial operation of the photoinjector is described. keywords: pbpl Download | Details | Edit | Delete
 title: The FINDER Photoinjector format: conference proceeding conference: PAC 2007 year: 2007 6 authors: | | | | | abstract: The FINDER photoinjector was developed for the inverse Compton scattering experiment under UCLA- LLNL collaboration. The improvements of this gun from SPARC gun [1, 2] at INFN-LNF (Frascati) and previous UCLA versions of the 1.6 cell S-band photoinjector are detailed here. The gun is designed to have large mode separation to suppress 0 mode excitation which may be a cause of the emittance degradation. In an effort to reduce the RF quadrupole effect the full cell tuners are replaced by vacuum ports. The laser ports are also omitted. Two openings of the solenoid shield are added to top and bottom of it where there were only two openings on the sides. S11 of the cavity was presented. The on-axis electric field was measured by the bead drop method to show the good field balance. The magnetic field in the emittance compensation solenoid was measured and the quadrupole components were derived. keywords: pbpl Download | Details | Edit | Delete
 title: Nuclear Photo-Science And Applications with Thomson-Radiated Extreme X-Ray (T-Rex) Sources format: conference proceeding conference: Linear Accelerator Conference 2006 year: 2006 15 authors: | | | | | | | | | | | | | | abstract: Recent advances in high brightness rf gun technology, coupled with novel laser systems and architecture have enabled the development of a new class of compact, tunable, monochromatic light sources capable of producing MeV photons with unprecedented brightness. Such new sources rely on Thomson scattering of incident photons produced by a TW-class laser off a bright relativistic electron beam to generate Doppler-upshifted photons in a highly collimated beam. Scaling laws [1] show that a frequency-doubled, 532 nm wavelength, 1 J, 10 ps Fourier transform-limited drive laser pulse interacting with a 250 MeV, 1 nC, 10 ps, 1 mm.mrad normalized emittance, with 0.1% relative energy spread, can yield a 2.24 MeV ?-ray flash with a peak brightness exceeding 1023 photons/[mm2 x mrad2 x s x 0.1% bandwidth]. This number is > 15 orders of magnitude beyond the output of a third-generation synchrotron at the same photon energy. Above ~ 100 keV, the photons can interact with nuclei, and nuclear applications become viable. In this paper, we present a technical overview of T- REX sources and their capabilities, and give a few examples of potential applications of interest. keywords: pbpl Download | Details | Edit | Delete
 title: Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES format: conference proceeding conference: PAC 2005 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. keywords: Download | Details | Edit | Delete
 title: Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system format: journal article publisher: Physical Review Special Topics - Accelerators and Beams 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. keywords: Download | Details | Edit | Delete
 title: Velocity bunching of high-brightness electron beams format: journal article publisher: Physical Review Special Topics - Accelerators and Beams 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. keywords: Download | Details | Edit | Delete
 title: Ultra-High Density Electron Beams for Beam Radiation and Beam Plasma Interaction format: conference proceeding conference: PAC 2005 year: 2005 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 Download | Details | Edit | Delete
 title: Production of femtosecond pulses and micron beam spots for high brightness electron beam applications format: conference proceeding conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams year: 2005 9 authors: | | | | | | | | abstract: keywords: pbpl Download | Details | Edit | Delete
 title: HIgh Energy, High Brightness X-Rays Produced by Compton Back Scattering at the Livermore PLEIADES facility format: conference proceeding conference: PAC 2005 year: 2005 11 authors: | | | | | | | | | | abstract: PLEIADES (Picosecond Laser Electron Interaction for the Dynamic Evaluation of Structures) produces tunable 30-140 keV x-rays with 0.3-5 ps pulse lengths and up to 10^7 photons/pulse by colliding a high brightness electron beam with a high power laser. The electron beam is created by an rf photo-injector system, accelerated by a 120 MeV linac, and focused to 20 ?m with novel permanent magnet quadrupoles. To produce Compton back scattered x-rays, the electron bunch is overlapped with a Ti:Sapphire laser that delivers 500 mJ, 100 fs, pulses to the interaction point. K-edge radiography at 115 keV on Uranium has verified the angle correlated energy spectrum inherent in Compton scattering and high-energy tunability of the Livermore source. Current upgrades to the facility will allow laser pumping of targets synchronized to the x-ray source enabling dynamic diffraction and time-resolved studies of high Z materials. Near future plans include extending the radiation energies to >400 keV, allowing for nuclear fluorescence studies of materials. keywords: pbpl Download | Details | Edit | Delete
 title: Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis format: journal article publisher: year: 2004 18 authors: | | | | | | | | | | | | | | | | | abstract: We present a detailed comparison of the measured characteristics of Thomson backscattered xrays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the xrays produced from the interaction are presented and shown to agree well with the simulations. keywords: pbpl Download | Details | Edit | Delete
 title: Short-pulse, high-brightness X-ray production with the PLEIADES Thomson-scattering source format: journal article publisher: Applied Physics B year: 2004 1 author: abstract: PLEIADES is a compact, tunable, high-brightness, ultra-short-pulse, Thomson-scattering X-ray source. Picosecond pulses of hard X-rays (10 keywords: Download | Details | Edit | Delete
 title: Pulse Compression via Velocity Bunching with the LLNL Thomson X-Ray Source Photoinjector format: conference proceeding conference: PAC 2003 year: 2003 5 authors: | | | | 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. keywords: Download | Details | Edit | Delete
 title: Generation of High Brightness X-Rays with the PLEIADES Thomson X-Ray Source format: conference proceeding conference: PAC 2003 year: 2003 14 authors: | | | | | | | | | | | | | 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. keywords: Download | Details | Edit | Delete
 title: Horizontal Phase-Space Distortions Arising from Magnetic Pulse Compression of an Intense, Relativistic Electron Beam format: journal article publisher: Physical Review Letters year: 2003 4 authors: | | | 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. keywords: Download | Details | Edit | Delete
 title: Ultrafast materials probing with the LLNL Thomson X-ray source format: conference proceeding conference: Linear Accelerator Conference 2002 year: 2002 24 authors: | | | | | | | | | | | | | | | | | | | | | | | 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. keywords: Download | Details | Edit | Delete
 title: Creation, Manipulation, and Diagnosis of Intense, Relativistic Picosecond Photo-electron Beams format: thesis year: 2002 1 author: 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. keywords: Download | Details | Edit | Delete
 title: Space-charge effects in high brightness electron beam emittance measurements format: journal article publisher: Physical Review Special Topics-Accelerators & Beams year: 2002 4 authors: | | | 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. keywords: Download | Details | Edit | Delete
 title: Electron Beam Production and Characterization for the PLEIADES Thomson X-Ray Source format: conference proceeding conference: AAC 2002 10th year: 2002 13 authors: | | | | | | | | | | | | abstract: We report on the performance of an S-band RF photocathode electron gun and accelerator for operation with the PLEIADES Thomson x-ray source at LLNL. Simulations of beam production, transport, and focus are presented. It is shown that a 1 ps, 500 pC electron bunch with a normalized emittance of less than 5 Tcmm-mrad can be delivered to the interaction point. Initial electron measurements are presented. Calculations of expected x-ray flux are also performed, demonstrating an expected peak spectral brightness of 1020 photons/s/mm2/mrad2/0.1% bandwidth. Effects of RF phase jitter are also presented, and planned phase measurements and control methods are discussed. keywords: Download | Details | Edit | Delete
 title: Commissioning of the Neptune photoinjector format: conference proceeding conference: PAC 2001 year: 2001 9 authors: | | | | | | | | 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). keywords: Download | Details | Edit | Delete
 title: Emittance measurements of the space charge dominated Thomson source photoinjector format: conference proceeding conference: PAC 2001 year: 2001 4 authors: | | | 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). keywords: Download | Details | Edit | Delete
 title: Commissioning and measurements of the Neptune photo-injector format: conference proceeding conference: AAC 2000 9th year: 2001 6 authors: | | | | | 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). keywords: Download | Details | Edit | Delete
 title: RF photoinjector development for a short-pulse, hard X-ray Thomson scattering source format: conference proceeding conference: AAC 2000 9th year: 2001 6 authors: | | | | | 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. keywords: Download | Details | Edit | Delete
 title: Nonequilibrium transverse motion and emittance growth in ultrarelativistic space-charge dominated beams format: journal article publisher: Physical Review Special Topics-Accelerators & Beams year: 2000 2 authors: | 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). keywords: Download | Details | Edit | Delete
 title: Non-equilibrium transverse motion and emittance growth in space-charge dominated beams format: conference proceeding conference: APS April Meeting year: 2000 2 authors: | 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. keywords: Download | Details | Edit | Delete
 title: Electron Beam Photocathode Cleaning format: conference proceeding conference: APS April Meeting year: 2000 7 authors: | | | | | | 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 keywords: Download | Details | Edit | Delete
 title: Commissioning of the Neptune Photoinjector format: conference proceeding conference: APS April Meeting year: 2000 13 authors: | | | | | | | | | | | | 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. keywords: Download | Details | Edit | Delete
 title: Single crystal copper photo-cathode in the BNL/SLAC/UCLA 1.6 cell RF gun format: conference proceeding conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd year: 2000 3 authors: | | 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. keywords: Download | Details | Edit | Delete
 title: Nonequilibrium transverse motion and emittance growth in space-charge dominated beams format: conference proceeding conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd year: 2000 2 authors: | 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). keywords: Download | Details | Edit | Delete
 title: Commissioning of the Neptune photoinjector format: conference proceeding conference: PAC 1999 year: 1999 21 authors: | | | | | | | | | | | | | | | | | | | | 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). keywords: Download | Details | Edit | Delete
 title: A Comparison Between the Performance of Split and Integrated RF Photoinjectors format: conference proceeding conference: PAC 1999 year: 1999 4 authors: | | | 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. keywords: Download | Details | Edit | Delete
 title: The effects of RF asymmetries on photoinjection beam quality format: conference proceeding conference: PAC 1999 year: 1999 4 authors: | | | 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). keywords: Download | Details | Edit | Delete
 title: Commissioning of the Neptune photoinjector format: conference proceeding conference: PAC 1999 year: 1999 21 authors: | | | | | | | | | | | | | | | | | | | | 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). keywords: Download | Details | Edit | Delete
 title: Optimal scaled photoinjector designs for FEL applications format: conference proceeding conference: PAC 1999 year: 1999 5 authors: | | | | 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. keywords: Download | Details | Edit | Delete
 title: A measurement of high gain SASE FEL induced electron beam micro-bunching using coherent transition radiation format: conference proceeding conference: PAC 1999 year: 1999 9 authors: | | | | | | | | 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). keywords: Download | Details | Edit | Delete
 title: Measured free-electron laser microbunching using coherent transition radiation format: conference proceeding conference: FEL 1998 20th year: 1999 9 authors: | | | | | | | | 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). keywords: Download | Details | Edit | Delete
 title: Measurements of gain larger than 10(5) at 12 mu m in a self-amplified spontaneous-emission free-electron laser format: journal article publisher: Physical Review Letters year: 1998 13 authors: | | | | | | | | | | | | abstract: We report measurements of very large output intensities corresponding to a gain larger than 10/sup 5/ for a single pass free-electron laser operating in the self-amplified spontaneous emission (SASE) mode at 12 mu m. We also report the observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. (18 References). keywords: Download | Details | Edit | Delete
 title: Measurements of High Gain and Intensity Fluctuations in a Self-Amplified, Spontaneous-Emission Free-Electron Laser format: journal article publisher: Physical Review Letters year: 1998 12 authors: | | | | | | | | | | | abstract: We report measurements of large gain for a single pass free-electron laser operating in self-amplified spontaneous emission (SASE) at 16 mm starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations. keywords: Download | Details | Edit | Delete
 title: Observation of Self-Amplified Spontaneous-Emission-Induced Electron-Beam Microbunching Using Coherent Transition Radiation format: journal article publisher: Physical Review Letters year: 1998 9 authors: | | | | | | | | abstract: We report the measurement of electron-beam microbunching at the exit of a self-amplified spontaneous-emission free-electron laser (SASE FEL), by observation of coherent transition radiation (CTR). The CTR was found to have an angular spectrum much narrower than spontaneous transition radiation and a narrow-band frequency spectrum. The central frequency of the fundamental CTR spectrum is found to differ slightly from that of the SASE, a finding in disagreement with previously invoked CTR theory. The CTR measurement establishes the uniformity of microbunching in the transverse dimension, indicating the SASE FEL operates in a dominant transverse mode. keywords: Download | Details | Edit | Delete
 title: The Neptune photoinjector format: conference proceeding conference: ICFA Second Generation Plasma Acceleration Workshop year: 1998 12 authors: | | | | | | | | | | | abstract: The RF photoinjector in the Neptune advanced accelerator laboratory, along with associated beam diagnostics, transport and phase-space manipulation techniques are described. This versatile injector has been designed to produce short-pulse electron beams for a variety of uses: ultra-short bunches for injection into a next-generation plasma beatwave acceleration experiment, space-charge dominated beam physics studies, plasma wake-field acceleration driver, plasma lensing, and free-electron laser microbunching techniques. The component parts of the photoinjector, the RF gun, photocathode drive laser systems, booster linac, RF system, chicane compressor, beam diagnostic systems, and control system, are discussed. The present status of photoinjector commissioning at Neptune is reviewed, and proposed experiments are detailed. (33 References). keywords: Download | Details | Edit | Delete
 title: Space charge dominated envelope dynamics of asymmetric beams in RF photoinjectors format: conference proceeding conference: PAC 1997 year: 1998 3 authors: | | abstract: While it has been proposed for several years that strongly asymmetric (sigma_x >> sigma_y) beams can be employed in RF photoinjectors to obtain asymmetric emittances for linear collider applications, it is known that the emittances obtained directly from RF photocathode guns are not suitably small for this purpose. Because of this, simulation work has been performed in an attempt to apply the principle of emittance compensation to recover the small and asymmetric emittances after suitable focusing and acceleration of photoinjector beams. In order to guide this difficult three-dimensional analysis, we present an extension of a previous theoretical model of the emittance compensation process in axisymmetric photoinjectors. In the extended model, we first analyze the general quadrupolar oscillations in a symmetric accelerating system, and then proceed to examine a propagation mode under asymmetric focusing. This mode is a generalization of the previously analyzed axisymmetric invariant envelope, allowing an optimization of the compensation process. Design philosophies, including rf cavity considerations, are included in the discussion. keywords: Download | Details | Edit | Delete
 title: Measurements of high gain and noise fluctuations in a SASE free electron laser format: conference proceeding conference: FEL 1997 19th year: 1998 12 authors: | | | | | | | | | | | abstract: We report measurements of large gain for a single pass free-electron laser operating in self-amplified spontaneous emission (SASE) at 16 mu m starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. (11 References). keywords: Download | Details | Edit | Delete
 title: Experimental confirmation of transverse focusing and adiabatic damping in a standing wave linear accelerator format: journal article publisher: Physical Review E year: 1997 10 authors: | | | | | | | | | abstract: The measurement of the transverse phase-space map, or transport matrix, of a relativistic electron in a high-gradient, radio-frequency linear accelerator (rf linac) at the UCLA photoinjector is reported. This matrix, which indicates the effects of acceleration (adiabatic damping), first-order transient focusing, and ponderomotive second-order focusing, is measured as a function of both rf field amplitude and phase in the linac. The elements of the matrix, determined by observation of centroid motion at a set of downstream diagnostics due to deflections induced by a set of upstream steering magnets, compare well with previously developed analytical theory [J. Rosenzweig and L. Serafini, Phys. Rev. E 49, 1599 (1994)]. The determinant of the matrix is obtained, yielding a direct confirmation of trace space adiabatic damping. Implications of these results on beam optics at moderate energy in high-gradient linear accelerators such as rf photoinjectors are discussed. keywords: Download | Details | Edit | Delete
 title: Measurements of high gain and noise fluctuations in a SASE free electron laser format: conference proceeding conference: Workshop on Single Pass, High Gain FELs Starting from Noise Aiming at Coherent X-Rays year: 1997 12 authors: | | | | | | | | | | | abstract: We report measurements of large gain for a single pass Free Electron Laser operating in Self Amplified Spontaneous Emission (SASE) at 16 mu m starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations. (11 References). keywords: Download | Details | Edit | Delete
 title: A high luminosity superconducting mini collider for phi meson production and particle beam physics format: conference proceeding conference: PAC 1991 year: 1991 14 authors: | | | | | | | | | | | | | abstract: A 510-MeV electron-positron collider has been proposed at the University of California at Los Angeles to study particle beam physics and phi-meson physics at luminosities larger than 1032 cm/sup -2/s/sup -1/. The collider consists of a single compact superconducting storage ring (SMC), with a bending field of 4 T and a current larger than 1 A. A discussion is presented of the main characteristics of this system and its major technical components: superconducting dipoles and the RF vacuum and injection systems. (6 References). keywords: Download | Details | Edit | Delete
 title: Progress in the Design of a DC FEL Power Source Using a Pelletron Driver format: conference proceeding conference: PAC 1987 year: 1987 7 authors: | | | | | | abstract: We discuss progress in the design of a DC Free Electron Laser power source using a Pelletron electrostatic accelerator as a driver. Such a power source should deliver up to 200 kW DC power in wavelengths ranging from a few microns to a few centimeters. The advantages of this system for use as a power source for future acceleration techniques are its efficiency, tunability and high average power. In order to achieve DC operation of the system extremely high electron recovery efficiencies are required. It is also likely that FEL operation will result in a large spread of electron energies. These design constraints require the development of a highly efficient electron beam collector as well as beam optics capable of recirculating beams with a large energy spread. We present collector and beamline designs and include electron optics studies for the full range of operating conditions. keywords: Download | Details | Edit | Delete