Results from the UCLA/FNPL underdense plasma lens experiment

A gaussian underdense plasma lens with peak density 5 x 10{sup 12} cm{sup -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 {sigma}{sub x,y} {approx} 650 {micro}m and {sigma}{sub z} {approx} 6.5 mm onto an optical transition radiation (OTR) screen {approx}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 {sigma}{sub r} within the beam

The UCLA/SLAC Ultra-High Gradient Cerenkov Wakefield Accelerator Experiment

An experiment is planned to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range. This new UCLA/SLAC/USC collaboration will take advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., {delta}{sub z} = 20 {micro}m at Q = 3 nC). The electron beam will be focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 {micro}m/OD = 325 {micro}m and ID = 100 {micro}m/OD = 325 {micro}m. The pulse length of the electron beam will be varied in order to alter the accelerating gradient and probe the breakdown threshold of the dielectric structures. In addition to breakdown studies, we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain information about the strength of the accelerating fields

Observations of underdense plasma lens focusing of relativistic electron beams

Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion

UCLA/FNPL Underdense Plasma Lens Experiment: Results and Analysis

Focusing of a 15 MeV, 16 nC electron bunch by a gaussian underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated. The strong 1.9 cm focal length plasma lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Time resolved measurements of the focused electron bunch are also reported and compared to simulations

Preliminary Results from the UCLA/SLAC Ultra-High Gradient CerenkovWakefield Accelerator Experiment

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., {sigma}{sub z} = 20 {micro}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 {micro}m/OD = 325 {micro}m and ID = 100 {micro}m/OD = 325 {micro}m. The pulse length of the electron beam was varied in the range 20 {micro}m < {sigma}{sub z} < 100 {micro}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

Ultra-High Gradient Dielectric Wakefield Accelerator Experiments

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., {sigma}{sub z} = 20 {micro}m at Q = 3 nC). The FFTB electron beam was successfully focused down and sent through short lengths of fused silica capillary tubing (ID = 200 {micro}m/OD = 325 {micro}m). 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

Ultra-High Gradient Dielectric Wakefield Accelerator Experiments

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., {sigma}{sub z} = 20 {micro}m at Q = 3 nC). The FFTB electron beam was successfully focused down and sent through short lengths of fused silica capillary tubing (ID = 200 {micro}m/OD = 325 {micro}m). 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

COMMISSIONING OF A HIGH-BRIGHTNESS PHOTOINJECTOR FOR COMPTON SCATTERING X-RAY SOURCES

Compton scattering of intense laser pulses with ultrarelativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. 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 accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described