Long Lifetime Optically Triggered Solid State Marx

Marx generators are used to produce high voltage, high current, short pulses for a variety of applications. High energy Marx generators are typically switched by gas insulated spark gaps, which have short lifetimes, <10⁵ pulses, thus limiting practical applications of the Marx generators. APP has developed optically triggered, economical, compact, 48 kV, >30 kA/mus, 8 kA, and 100 ns turn-on solid state switches and examined their performance under normal and fault-mode operating conditions in Marx generators. With 48 kV compact solid state switches, >10⁷ pulse lifetime, high voltage Marx generators capable of high pulse repetition rates can be built. Three different Marx configurations have been tested; a conventional unipolar Marx, a unipolar Marx that uses magnetic assist to achieve >70 kA/mus current risetimes, and an inverting LC mode. For practical applications, solid state switches must survive system faults, such as shorts in downstream components or the load, which can result in twice the normal forward current, a large reverse current and with a large fraction of the system energy deposited in the switches. The switches should also tolerate trigger failures that can result in overvoltaging of one or more switches. This paper will include a description of the solid state Marx and triggering system and show data from multi-million pulse operation as well as fault mode survival testing such as load shorts and switch triggering failures. Near-term applications for the switches include the retro-fitting of the 5 pps Marxes used for the Electra laser pre-amplifier and main amplifier. Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory. This program is developing technologies to meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. The technologies developed on Electra should be directly scalable to a full size fusion power plan- - t beam line. The present Electra Marxes use gas insulated spark gap switches with lifetimes of 10⁵ pulses. By using the 48 kV Compact Solid State switch, lifetimes in excess of 10⁷ pulses are expected.