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44 papers
| title: | Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation |
| format: | conference procceeding |
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| 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: | Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators |
| format: | journal article |
| year: | 2005 |
| 5 authors: | | | | | |
| abstract: | Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear collider have included intense electron beams with densities many times in excess of the plasma density. The beam’s electric fields expel the plasma electrons from the beam path to many beam radii in this regime. We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA collider scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are presented. Implications of ion motion on the feasibility of the PWFA-based colliders are discussed. |
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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: | 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: | The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 4 authors: | | | | |
| 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 |
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| title: | Plasma density transition trapping as a possible high-brightness electron beam source |
| format: | journal article |
| year: | 2004 |
| 3 authors: | | | |
| 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-of principle transition trapping experiment is planned for the near future. The proposed experiment is described in detail. |
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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: | Procedure for the production of a 10 micron aluminum foil OTR window |
| format: | tech note |
| year: | 2004 |
| 1 author: | |
| abstract: | |
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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: | Plasma Density Transition Trapping of Electrons in Plasma Wakefield Accelerators |
| format: | thesis |
| year: | 2004 |
| 1 author: | |
| 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. |
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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: | 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: | The UCLA/NICADD Plasma Density Transition Trapping Experiment |
| format: | talk |
| year: | |
| 1 author: | |
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| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulations, Scaling, and Accelerating Wakefields |
| format: | preprint |
| year: | 2004 |
| 4 authors: | | | | |
| abstract: | The energy loss and gain of a beam in the nonlinear, ‘‘blowout’’ regime of the plasma wakefield accelerator, which features ultrahigh accelerating fields, linear transverse focusing forces, and nonlinear plasma motion, has been asserted, through previous observations in simulations, to scale linearly with beam charge. Additionally, from a recent analysis by Barov et al., it has been concluded that for an infinitesimally short beam, the energy loss is indeed predicted to scale linearly with beam charge for arbitrarily large beam charge. This scaling is predicted to hold despite the onset of a relativistic, nonlinear response by the plasma, when the number of beam particles occupying a cubic plasma skin depth exceeds that of plasma electrons within the same volume. This paper is intended to explore the deviations from linear energy loss using 2D particle-in-cell simulations that arise in the case of experimentally relevant finite length beams. The peak accelerating field in the plasma wave excited behind the finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude into the nonlinear regime. At large enough normalized charge, the linear scaling of both decelerating and accelerating fields collapses, with serious consequences for plasma wave excitation efficiency. Using the results of parametric particle-in-cell studies, the implications of these results for observing severe deviations from linear scaling in present and planned experiments are discussed. |
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| title: | The UCLA/NICADD Plasma Density Transition Trapping Experiment |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| 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. |
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| title: | Horizontal Phase-Space Distortions Arising from Magnetic Pulse Compression of an Intense, Relativistic Electron Beam |
| format: | journal article |
| 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. |
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| title: | New Vacuum Chamber for the Plasma Density Transition-Trapping Experiment |
| format: | tech note |
| year: | 2003 |
| 2 authors: | | |
| 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. |
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| title: | Energy Loss and Accelerating Field in the Plasma Wakefield Accelerator |
| format: | preprint |
| year: | 2003 |
| 4 authors: | | | | |
| abstract: | |
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| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulation |
| format: | conference procceeding |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year: | 2003 |
| 3 authors: | | | |
| abstract: | There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron 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. |
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| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis |
| format: | conference procceeding |
| conference: | ICFA Workshop on Physics and Applications of High Brightness Electron Beams |
| year: | 2003 |
| 3 authors: | | | |
| abstract: | There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron 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. |
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| title: | Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 2 authors: | | |
| 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 1014 A= mrad 2. A proof-ofprinciple transition trapping experiment is planned for the near future. The proposed experiment is described in detail. |
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| title: | Plasma Wakefield Experiments |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 6 authors: | | | | | | |
| abstract: | |
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| title: | Longitudinal Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 3 authors: | | | |
| abstract: | |
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| title: | Velocity bunching experiment at the Neptune Laboratory |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 5 authors: | | | | | |
| abstract: | |
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| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Nonlinear plasma response and linear scaling |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 4 authors: | | | | |
| abstract: | |
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| title: | Beam-plasma interaction experiments at the UCLA Neptune Laboratory |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| 5 authors: | | | | | |
| 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. |
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| title: | Dynamics of a Driver Beam Propagating in an Underdense Plasma with a Downward Density Transition |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| 7 authors: | | | | | | | |
| 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. |
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| title: | Commissioning of the Neptune photoinjector |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| 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). |
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| title: | Production and synchronization of electron beams from RF photoinjector/compressor systems for ultra-fast applications |
| format: | conference procceeding |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| year: | 2001 |
| 2 authors: | | |
| 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. |
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| title: | Commissioning and measurements of the Neptune photo-injector |
| format: | conference procceeding |
| conference: | 9th Advanced Accelerator Concepts Workshop |
| 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). |
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| title: | Observation and analysis of self-amplified spontaneous emission at the APS low-energy undulator test line |
| format: | conference procceeding |
| conference: | 22nd International Free Electron Laser Conference |
| year: | 2001 |
| 153 authors: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| abstract: | Exponential growth of self-amplified spontaneous emission at 530 nm was first experimentally observed at the Advanced Photon Source low-energy undulator test line in December 1999. Since then, further detailed measurements and analysis of the results have been made. Here, we present the measurements and compare these with calculations based on measured electron beam properties and theoretical expectations. (31 References). |
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| title: | Electron Beam Photocathode Cleaning |
| format: | conference procceeding |
| 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 |
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| title: | Commissioning of the Neptune Photoinjector |
| format: | conference procceeding |
| 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. |
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| title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma |
| format: | preprint |
| year: | 2000 |
| 3 authors: | | | |
| 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. |
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| title: | Commissioning of the Neptune photoinjector |
| format: | conference procceeding |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| 21 authors: | | | | | | | | | | | | |