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Strained-layer GaAs photocathodes are used at Jefferson Lab to obtain highly polarized electrons. Exposure to atomic hydrogen (or deuterium) is used to clean the wafer surface before the activation with cesium and nitrogen trifluoride to consistently produce high quantum yield photocathodes. The hydrogen-cleaning method is easy, reliable and inexpensive. However, recent tests indicate that exposure to atomic hydrogen may affect the polarization of the electron beam. This paper presents preliminary results of a series of tests conducted to study the effect of atomic H exposure on the polarized electron beam from a strained-layer GaAs sample. The experimental setup is described and the first measurements of the beam polarization as a function of exposure dose to atomic hydrogen are presented. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Outgassing measurements of three UHV materials (304 Stainless Steel (SS), 316L SS and 6061T-6 aluminum) were made using the conductance and accumulation techniques as given in the AVS Recommended Practice for Outgassing Measurements [1]. Measurement results indicate good agreement between the two techniques. This study was undertaken to help determine the vacuum limitations of the photoelectron guns used at Jefferson Lab and to aid in the choice of vacuum chamber materials that will be used in the construction of future photoelectron guns. The outgassing rate measured for all of the chamber materials, regardless of technique, was about 1×l0[SUP-12] Torr&mdot;l/s&mdot;cm[SUP2]. [ABSTRACT FROM AUTHOR]

The polarized photoinjector at Jefferson Lab continues to provide high average current, high polarization, high quality beam to nuclear physics Users in as many as three endstations simultaneously. Long lifetime operation has been obtained from two identical polarized guns. A new high power modelocked ti-sapphire laser has been constructed to enhance the effective operating lifetime of the photoinjector. Efforts to enhance beam polarization and reduce helicity correlated beam systematic effects are underway. [ABSTRACT FROM AUTHOR]