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abstract:
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We describe a system designed for photocathode testing
and beam dynamics studies which is based on a high
voltage extractor and a sub–ps drive laser. The system’s
distinctive characteristics are the ability to run in the short
bunch regime — where the dynamics are not governed by
the Child–Langmuir law — and the anticipated
availability of both transverse and longitudinal beam
diagnostics to determine the full beam distribution. The
system consists of a pseudo parallel plate 100 kV DC gun
with a removable cathode and a cathode–anode gap of
8 mm, yielding a cathode field of up to 10 MV/m. The
drive laser is a Nd:Glass system capable of producing
over 200 μJ at 264 nm with a pulse length adjustable from
approximately 250 fs to over 1 ps. The goals of the
system, described in this paper, are to support ongoing
photocathode studies, including measuring high current
density extraction from prepared cathodes and
investigating the effect of surface variation of the
quantum efficiency. Additional studies foreseen include
parameterizing the effect of surface variations on the
transverse emittance, and exploring beam dynamics such
as the short bunch blow out regime which has recently
been proposed as a way to produce uniform ellipsoidal
charge density distributions[1].
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