  For the Low Emittance Gun (LEG) project at Paul Scherrer Institute a stable
and reliable high voltage pulsed generator was needed in order to study low
emittance beams generation and transport. The system had to provide variable
asymmetric voltage pulse up to -500 kV with amplitude stability better than 1.2
part per thousand (ppt). The pulse should be applied to the cathode of variable
gap accelerating diode providing voltage gradients up to more than 100 MV/m. A
broad bandwidth electrical connection to the cathode is necessary in order to
deliver fast cathode gating signal. The design of the pulser is presented as
well as the optimization and implementation of some critical components in the
system. A detailed electrical model of the pulsed generator was created in
order to optimize and study its electrical behavior. The measured waveforms are
compared to the simulated ones and output amplitude stability is discussed.
Different electrode materials and surface treatments were studied to ensure
breakdown free operation of the gun at high electrical gradients. Diamond Like
Carbon (DLC) coating has shown excellent vacuum gap insulation capabilities
reaching surface breakdown electric field of more than 250 MV/m. The designed
high voltage system showed very good stability and reliability and it was a
useful tool for many cathode and electron beam studies.
