Characterization of a 200-nF unipolar, high current, low inductance capacitor switch assembly.

Abstract

Capacitor switch assemblies (CSAs) are a viable alternative to the standard Linear Transformer Driver (LTD) brick-the prime power "building block" in LTD-based high current drivers. In a CSA, the geometrical advantages combined with the switch's placement within a CSA produce a significantly lower inductance structure compared to the LTD brick. Lower inductances enable higher peak currents and faster rise times when all other parameters are held constant, thus making low inductance a crucial feature in high current systems. In this article, the experimental characterization of a 200-nF, 38-nH CSA is presented. When charged to 56 (57 kV), this CSA generates a 76 (64-kA) current peak into 0.28 (0.46-Ω) resistive loads. Comparing the experimental data's waveforms with those of an analytic circuit model, close agreement with underdamped RLC circuit theory is obtained. Based on this CSA's performance, the experimental data are extrapolated to model the performance of a bipolar 100-nF (±90 kV) CSA and a unipolar 200-nF (90 kV) CSA and compared with a standard 40-nF, bipolar (±100 kV) LTD brick. Furthermore, circuit simulations are performed for a 2.2-m diameter LTD cavity with 20 dual polarity (±100 kV) standard bricks and 23 dual polarity (±90 kV) CSAs. An increase by a factor of 2 in the power output is obtained for the CSA-LTD cavity over the brick LTD cavity while maintaining the same cross-sectional area. This has a large potential impact on the pulsed power generator design, both for smaller university-scale machines and proposed next-generation [60 Mega Amp (MA)] accelerators.