ZR laser triggered gas switch requirements and performance

Abstract

Summary form only given. The Z machine at Sandia National Laboratories is presently undergoing an upgrade, called Z-Refurbishment (ZR), that is aimed at improving capacity, precision, and capability to nearly all of its pulsed power components, including its thirty six laser-triggered gas switches (LTGS). Voltage and current requirements for the ZR LTGS have increased 25% from the onset of the ZR program, with no allowable increase to the physical footprint (or inductance) for the device. Initial design studies indicated that a total machine peak current of 26 MA could be achieved with each LTGS operating at 5 MV and 600 kA. Increases in the final design inductance in the transition from vertical water transmission lines to horizontal magnetically insulated transmission lines, higher inductance in vacuum from changes in the load position for improved diagnostic access, and conservatism in the vacuum power How requirements caused the LTGS operations goals to become 6.25 MV and 750 kA for a total machine peak current of 26 MA. Tests of the proposed switch design at 5 MV with a resistive load demonstrated jitter (<4 ns), voltage precision (range 0.05 -1.5 percent), and lifetime (mean 220 shots), which were all within the initial ZR design goals. The prefire rate was 1.2% which was substantially higher than desired for ZR. Subsequent tests on a single ZR engineering module as the operating voltage increased resulted in random housing flashovers, difficulties in consistently triggering the switch and even higher prefire rate. This paper summarizes LTGS design changes and new cleaning/assembly protocols that were developed to meet evolving ZR goals. Performance of LTGS at 5.2 MV and 6.1 MV on the engineering module are discussed. The data are utilized to project performance on ZR.