High Power Pulsed Supply for Electron Beam Generation

Abstract

Summary form only given. The latest results from our 450 kV, 70 kA, 240 ns pulsed power supply are presented. This power supply has been used to produce a 2 kA electron beam to drive a Free Electron Maser and produce high power (60 MW) coherent microwave radiation from a highly oversized cavity. Future developments require a reduction in power supply size and weight, increased repitition rate operation and increased electron beam current. We propose to achieve these aims with a combination of increased energy efficiency and the use of a novel design of transmission line transformer. The proposed new supply will use self sharpening "shocklines" as the transformer elements to achieve fast rise time high voltage pulses. We show that a passive tailbiter can be created by control of the secondary mode of the transmission line transformer, this tailbiter may be tuned to alter the pulse length. It is well known that the input impedance of a transmission line transformer decreases proportionately with increasing number of transmission lines. As voltage gain is determined by the number of cables, high voltage gain transmission line transformers exhibit unpleasantly low input impedance and producing sufficient drive becomes problematic. This can be ameliorated by the use of multiple parallel input circuits and switches, but low impedance drivers are still needed. We present a design of compact, low-impedance transmission line suitable as a pulse input source. The current power supply uses high pressure spark gaps as switches in both the Marx bank and the transmission line output. As the operation of spark gaps at high pulse repitition frequency (prf) is problematic we have considered alternative switching methods. IGBT switches or parallel IGBT switches are capable of high current, low loss switching when stacked with appropriate trigger and control circuitry. These solid state switches can be used as an alternative to conventional thyratron switches, though not necessarily at lower cost. Both of these options could be used for high prf operation.