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Machie, D.

Paper Title Page
THPMS064 Lifetime Measurements of High Polarization Strained-Superlattice Gallium Arsenide at Beam Current > 1 Milliamp using a New 100kV Load Lock Photogun 3130
  • J. M. Grames, P. A. Adderley, J. Brittian, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M. L. Stutzman, R. Suleiman, K. E.L. Surles-Law
    Jefferson Lab, Newport News, Virginia
  Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.

A new 100 kV GaAs DC Load Lock Photogun has been constructed at Jefferson Laboratory, with improvements for photocathode preparation and for operation in a high voltage, ultra-high vacuum environment. Although difficult to gauge directly, we believe that the new gun design has better vacuum conditions compared to the previous gun design, as evidenced by longer photocathode lifetime, that is, the amount of charge extracted before the quantum efficiency of the photocathode drops by 1/e of the initial value via the ion back-bombardment mechanism. Photocathode lifetime measurements at DC beam intensity of up to 10 mA have been performed to benchmark operation of the new gun and for fundamental studies of the use of GaAs photocathodes at high average current*. These measurements demonstrate photocathode lifetime longer than one million Coulombs per square centimeter at a beam intensity higher than 1 mA. The photogun has been reconfigured with a high polarization strained superlattice photocathode (GaAs/GaAsP) and a mode-locked Ti:Sapphire laser operating near band-gap. Photocathode lifetime measurements at beam intensity greater than 1 mA are measured and presented for comparison.

"Further Measurements of Photocathode Operational Lifetime at Beam Intensity >1mA using the CEBAF 100 kV DC GaAs Photogun", J. Grames et al., Proc. of the 17th Inter. Spin Symposium, Japan (2006).