A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z    

Brittian, J.

Paper Title Page
WPAP045 Ion Back-Bombardment of GaAs Photocathodes Inside DC High Voltage Electron Guns 2875
 
  • J.M. Grames, P. Adderley, J. Brittian, D. Charles, J. Clark, J. Hansknecht, M. Poelker, M.L. Stutzman, K.E.L. Surles-Law
    Jefferson Lab, Newport News, Virginia
 
  Funding: This work was supported by U.S. DOE Contract No. DE-ACO5-84-ER40150.

The primary limitation for sustained high quantum efficiency operation of GaAs photocathodes inside DC high voltage electron guns is ion back-bombardment of the photocathode. This process results from ionization of residual gas within the cathode/anode gap by the extracted electron beam, which is subsequently accelerated backwards to the photocathode. The damage mechanism is believed to be either destruction of the negative electron affinity condition at the surface of the photocathode or damage to the crystal structure by implantation of the bombarding ions. This work characterizes ion formation within the anode/cathode gap for gas species typical of UHV vacuum chambers (i.e., hydrogen, carbon monoxide and methane). Calculations and simulations are performed to determine the ion trajectories and stopping distance within the photocathode material. The results of the simulations are compared with test results obtained using a 100 keV DC high voltage GaAs photoemission gun and beamline at currents up to 10 mA DC.