Pulsed Power for High Power Electron-Beam Pumped Lasers

Abstract

A primary consideration for operation of many high power gas lasers is the generation of a high voltage, large area electron beam. Beam parameters are dictated by laser requirements. Historically the electrical system typically has consisted of a Marx generator with pulse shaping stages or a pulse forming line. In the latter case, one or more high voltage switches (spark gaps) are required. Generally, these systems have been single pulse with cold cathode diodes. For repetitive systems, there is a trend to replace the Marx generator with a pulse transformer. For long pulses and large diode impedances, the pulse shaping elements can be placed in the transformer primary circuit. Otherwise, a PFL and high voltage switch are still required. The trend in pulsed power systems is to attempt to increase the range over which the PFL is not required. For short pulses (10's of nanoseconds), cold cathodes provide a stable impedance for at least hundreds of thousands of shots at rates to several tens of hertz. For longer pulses, where impedance collapse becomes a problem, the shot life of cold cathodes becomes short and the use of hot cathodes may be necessary. In either case, issues of beam current uniformity over large areas (including control of pinching) and mitigation of arc formation must be addressed. This paper will review on-going work relevant to the electrical systems and beam sources. State-of-the-art will be described and a modest attempt will be made to extrapolate current trends.