Polarization studies of strained GaAs photocathodes at the SLAC Gun Test Laboratory

Abstract

The SLAC Gun Test Laboratory apparatus, the first two meters of which is a replica of the SLAC injector, is used to study the production of intense, highly-polarized electron beams required for the Stanford Linear Collider and future linear colliders. The facility has been upgraded with a Mott polarimeter in order to characterize the electron polarization from photocathodes operating in a DC gun. In particular, SLAC utilizes p-type, biaxially-strained GaAs photocathodes which have produced longitudinal electron polarizations greater than 80% while yielding pulses of 5 A/cm 2 at an operating voltage of 120 kV. Among the experiments performed include studying the influences of the active layer thickness, temperature, quantum efficiency and cesiation on the polarization. The results might help to develop strained photocathodes with higher polarization.

Upgraded photon calorimeter with integrating readout for the Hall A Compton polarimeter at Jefferson Lab

“…In this plot, the vertical dashed lines mark when the laser spot was moved at the accelerator source; there is a distinct measured change in polarization behavior following spot moves [20]. The observed gradual increase in polarization following spot moves is consistent with a gradual degradation of the photocathode surface, which has been observed to increase electron polarization while the quantum efficiency drops [21,22]. The photon arm of the Compton polarimeter has measured the average beam polarization over the HAPPEX-III run to be [89.41 ± 0.05(stat) ± 0.84(sys) ± 0.18(gaps)]%.…”

SLAC's polarized electron source laser system and minimization of electron beam helicity correlations for the E-158 parity violation experiment

“…§ For 1 cm 1/e 2 diameter. Adapted from [16]. cathode), providing additional flexibility in optimizing the optics system.…”

“…A diagram of the bandgap and energy levels for strained GaAsP. The arrows indicate the allowed transitions for right-and left-helicity photons of λ = 805 nm.Adapted from[16].…”