Tesla transformer based 500 kv pulser for low emittance test stand at Paul Scherrer Institute

Abstract: 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.