Synchronous photoinjection using a frequency-doubled gain-switched fiber-coupled seed laser and ErYb-doped fiber amplifier

Light at 1560 nm from a gain-switched fiber-coupled diode laser and ErYb-doped fiber amplifier was frequency doubled to obtain over 2 Waverage power at 780 nm with ~40 ps pulses and pulse repetition rate of 499 MHz. This light was used to drive the 100 kV DC high voltage GaAs photoemission gun at the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory to produce a high average current beam (100 μA) of highly spin-polarized electrons ( \u3e 80%). This new drive-laser system represents a significant advance over laser systems used previously, providing significantly higher power and enhanced reliability

Synchronous photoinjection using a frequency-doubled gain-switched fiber-coupled seed laser and ErYb-doped fiber amplifier

Light at 1560 nm from a gain-switched fiber-coupled diode laser and ErYb-doped fiber amplifier was frequency doubled to obtain over 2 Waverage power at 780 nm with ~40 ps pulses and pulse repetition rate of 499 MHz. This light was used to drive the 100 kV DC high voltage GaAs photoemission gun at the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory to produce a high average current beam (100 μA) of highly spin-polarized electrons ( \u3e 80%). This new drive-laser system represents a significant advance over laser systems used previously, providing significantly higher power and enhanced reliability

Correlation of CsK2Sb Photocathode Lifetime With Antimony Thickness

CsK2Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali

Electrostatic Design and Conditioning of a Triple Point Junction Shield for a −200 kV DC High Voltage Photogun

Nuclear physics experiments performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at the Jefferson Lab require a DC high voltage photogun to generate polarized electron beams from GaAs photocathodes. The photogun uses a tapered ceramic insulator that extends into the vacuum chamber and mechanically holds the cathode electrode. Increasing the operating voltage from nominal −130 kV to −200 kV will provide lower beam emittance, better transmission through injector apertures, and improved photocathode lifetime. This desire to increase the photogun operating voltage led to the design of a triple-point-junction shield electrode which minimizes the electric field at the delicate insulator-metal-vacuum interface and linearizes the potential across the insulator, thus reducing the risk of arcing along the ceramic insulator. This work describes the results obtained using COMSOL® electrostatic-field simulation software and presents the high voltage conditioning results of the upgraded −200 kV CEBAF photogun. Published by AIP Publishing

Search for spin-polarized photoemission from GaAs using light with orbital angular momentum

Laser light with photon energy near the band gap of GaAs and in Laguerre-Gaussian modes with different amounts of orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree of electron spin polarization was measured using a micro-Mott polarimeter and found to be consistent with zero with an upper limit of ∼3% for light with up to ±5h of orbital angular momentum. In contrast, the degree of spin polarization of 32.3 ± 1.4% using circularly polarized laser light at the as the same wavelength, which is typical for bulk GaAs photocathodes

Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun

Polarization in Heavy Ion Physics

Role of polarization studies in heavy ion physics is discussed with emphasis on the search for quark-gluon plasma formation and studies of its dynamical properties.Comment: 6 pages, 5 figures, plenary talk at the 18th International Symposium on Spin Physics, October 6-11, 2008, University of Virginia, Charlottesville, US

Unique Electron Polarimeter Analyzing Power Comparison and Precision Spin-Based Energy Measurement

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Moller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise ( better than 10-4) absolute measurement of the final electron beam energy