A new 100 kV GaAs DC
load locked photogun has been constructed and is run in the Test Lab
for commissioning purposes and to study photocathodes producing up to
10 mA. The load locked design offers significant improvements compared
with the two electron guns presently used for CEBAF operation and is
planned for installation in 2007. Improvements
of photocathode handling, processing and operation in a high voltage,
high vacuum environment will be described.
A
series of photocathode lifetime measurements were performed at DC beam
current to 10 mA to benchmark operation of the new gun and for
fundamental studies of the operation of GaAs photocathodes at high
average current. Although difficult to gauge directly, we believe the
new gun design has better vacuum conditions compared to the previous
gun design, which is studied by means of photocathode lifetime. In addition, lifetime measurements were
performed using an activated photocathode coated with hydrogen. These photocathodes begin with lower quantum
efficiency, but exhibit increased yield when damaged, and consequently
enhanced operational lifetime. Finally,
lifetime measurements were performed using a biased anode electrode, to
investigate quantum efficiency decay associated with ion production
outside the gun vacuum chamber.
Finally,
I will present some highlights of the Polarized Electron Source meeting
in Kyoto, Japan, specifically discussion of polarized
electron and positron
sources for the International Linear Collider.
