First Name: R.
Middle Name:
Last Name: Yoder
Full Name: R. Yoder
tags:
Potential Duplicate Authors:
view citation format
12 papers
| 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. |
| keywords: | |
| Download | View | Details | edit | delete | |
| 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. |
| keywords: | |
| Download | View | Details | edit | delete | |
| 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. |
| keywords: | |
| Download | View | Details | edit | delete | |
| 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. |
| keywords: | |
| Download | View | Details | edit | delete | |
| title: | Acceleration of Injected Electrons In A Laser Beatwave Experiment |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 10 authors: | | | | | | | | | | |
| abstract: | Plasma-based accelerators of particles are of great interest because plasmas can sustain very strong electric fields. They are utilizing a relativistic plasma wave with a phase velocity close to the speed of light driven by a high-power laser beam. The Neptune Laboratory at UCLA is being used for plasma beatwave acceleration of injected electrons. Here, a two-wavelength laser pulse (frequencies w1,w2) resonantly drives a longitudinal electron plasma wave of frequency equal to w1-w2, providing a field strength of GeV/m and, therefore, accelerates an injected electron beam at this very high gradient. A 10 ps beam of 12 MeV electrons is loaded in a 3-cm long plasma beatwave accelerator driven by a TW CO2 laser pulse. At the resonance condition, the electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that for large volume diffraction limited plasmas, when efficiency of the plasma wave excitation is restricted by ionization-induced refraction, acceleration of electrons is enhanced significantly by using asymmetric (fast front and slow fall) long pulses. 2D PIC simulations revealed that guiding of the laser pulse in a ponderomotive, self-induced ion channel, formed ~200 ps after the field ionization, allows compensation for the ionization-induced defocusing and efficient driving of the beatwave over the entire length. |
| keywords: | |
| Download | View | Details | edit | delete | |
| title: | Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 4 authors: | | | | |
| abstract: | We have recently added a dispersionless translating section to the UCLA Neptune linear accelerator beamline. This new section of beamline will serve as a venue for beam shaping and compression experiments using the 14MeV electron beam produced by the UCLA Neptune PWT linac and newly installed photoinjector. An examination of the first and second-order optics indicates that when certain nonlinear effects are minimized through the use of sextupole magnets, the longitudinal dispersion is dominated by a negative R56 which, for an appropriately chirped initial beam, can be used to create a ramped beam of a few picosecond duration that would be ideal for driving large amplitude wake fields in a plasma and producing high transformer ratios. The beamline is now in operation. Preliminary data indicate that the beamline optics are well-predicted by simulation and that sextupoles can be used successfully to eliminate nonlinear horizontal dispersion. Future experiments are planned for measuring beam compression (using CTR autocorrelation) and doing longitudinal phase space tomography (using a transverse deflecting cavity). |
| keywords: | |
| Download | View | Details | edit | delete | |
| 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. |
| keywords: | |
| Download | View | Details | edit | delete | |
| title: | Very High Energy Gain at the Neptune Inverse Free Electron Laser Experiment |
| format: | journal article |
| year: | Dec 2004 |
| 16 authors: | | | | | | | | | | | | | | | | |
| abstract: | We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 µm laser with power larger than 400 GW. The Rayleigh range of the laser, ~ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Three-dimensional simulations, in good agreement with the measured electron energy spectrum, indicate that most of the acceleration occurs in the first 25 cm of the undulator, corresponding to an energy gradient larger than 70 MeV/m. The measured energy spectrum also indicates that higher harmonic Inverse Free Electron Laser interaction takes place in the second section of the undulator. |
| keywords: | pbpl |
| Download | View | Details | edit | delete | |
| title: | Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures |
| format: | journal article |
| year: | 2007 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | An experiment designed to test the breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been completed. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 μm. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compres- sion of the electron bunch. 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 multi-GV/m sur- faced fields that were sustained equate to on axis accelerat- ing field of several GV/m. |
| keywords: | pbpl |
| Download | View | Details | edit | delete | |
| title: | Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures |
| format: | conference procceeding |
| conference: | PAC07 |
| year: | 2007 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | An experiment designed to test the breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been completed. In this experiment at the Final Focus Test Beam (FFTB) facility, the 28.5 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 μm. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compres- sion of the electron bunch. 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 multi-GV/m sur- faced fields that were sustained equate to on axis accelerat- ing field of several GV/m. |
| keywords: | pbpl |
| Download | View | Details | edit | delete | |
| title: | Ultra-high gradient dielectric wakefield accelerator experiments |
| format: | journal article |
| year: | 2006 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | Ultra-high gradient dielectric wakefield accelerators are a potential option for a linear collider afterburner since they are immune to the ion collapse and electron/positron asymmetry problems implicit in a plasma based afterburner. 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. The experiment took advantage of the unique SLAC FFTB electron beam and its ultra-short pulse lengths and high currents (e.g., σz = 20 μm at Q = 3 nC). The FFTB electron beam was successfully focused down and sent through short lengths of fused silica capillary tubing (ID = 200 μm / OD = 325 μm). The pulse length of the electron beam was varied to produce 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 being developed for the SLAC SABER and BNL ATF we plan to use the coherent Cerenkov radiation emitted from the capillary tube as a field strength diagnostic and demonstrate GV/m range particle energy gain. |
| keywords: | pbpl |
| Download | View | Details | edit | delete | |
| title: | High Energy gain IFEL at the UCLA Neptune Laboratory |
| format: | journal article |
| year: | |
| 16 authors: | | | | | | | | | | | | | | | | |
| abstract: | We report on the observation of energy gain in excess of 20MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5MeV electron beam is injected in a 50cm longundulator strongly tapered both in period and field amplitude. A CO210.6μm laser with power > 400GW is used as the IFEL driver. The Rayleigh range of the laser(∼1.8cm)is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped instable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. Anenergygradientof>70MeVisinferred. In these cond section of the undulator higher harmonic IFEL interaction is observed. |
| keywords: | |
| Download | View | Details | edit | delete | |