Investigation of the effects of waterline switch capacitance on the electrical prepulse of the Z-accelerator

The Z-accelerator at the Sandia National Laboratories (SNL) was modified in 1996 to deliver a 20 MA pulse to a Z-pinch load in 100 ns. The pulsed-power driver is a 36 module waterline accelerator. Each waterline contains four self-break switches as part of the pulse-forming section. A study was conducted to investigate the effects of increasing the capacitance of the waterline switches on the shape of the electrical prepulse at the load. Past studies have shown that increasing the prepulse at the Z-pinch load increases the X-ray output power. In this study, one set of switches with its surrounding waterline hardware was modeled in 3D and capacitance calculated using the electrostatic code, COULOMB. The capacitance values were used in a SCREAMER model of the Z-accelerator. SCREAMER, an SNL-developed, lumped-element circuit code was used to calculate the time-dependent current waveforms delivered to the Z-pinch load. The design was changed and a new capacitance matrix and output waveforms were calculated. This paper presents the results of the COULOMB 3-D modeling, and the SCREAMER circuit model analyses.