Polarization and charge limit studies of strained GaAs photocathodes

Technical Report · Sat Mar 01 04:00:00 EST 1997

DOI:https://doi.org/10.2172/486020· OSTI ID:486020

Saez, P J

This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of {approximately} 2.5 A/cm{sup 2} at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don`t have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes.

• Research Organization: Stanford Linear Accelerator Center, Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Research, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00515
• OSTI ID: 486020
• Report Number(s): SLAC-R--501; ON: DE97006543
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ELECTRON BEAMS
ELECTRON SOURCES
GALLIUM ARSENIDES
PARAMETRIC ANALYSIS
PHOTOCATHODES
POLARIZATION
POLARIZED BEAMS