ZR Marx capacitor lifetime test results

The ZR upgrade to the Z machine at Sandia National Labs (SNL) has a total output current requirement of at least 26 MA for a 100-ns standard z-pinch load. To accomplish this with minimal impact on the surrounding hardware, the existing Marx generator capacitors must be replaced with identical size units with twice the capacitance. Before the 2005 six-month shut down and transition from Z to ZR occurs, 2500 of these capacitors will be delivered. This paper summarizes the results of our lifetime testing of the selected General Atomics P/N 32896. 11×14×25-inch, Scyllac-style insulator bushing, 2.65-μF, 100-kV, 30-nH, 35% reversal capacitor. We have completed lifetime tests with twelve capacitors at 100 kV and with fourteen capacitors at 110-kV charge voltage. The means of the fitted Weibull distributions for these two cases are about 17,000 and 10,000 shots, respectively. As a result of this effort plus the rigorous vendor testing prior to shipping, we are confident in the high reliability of these capacitors and have acquired information pertaining to their lifetime dependence on the operating voltage. One result of the analysis is that for these capacitors lifetime scales inversely with voltage to the 6.28±0.9 power, over this 100 to 110-kV voltage range. Accepting the assumptions leading to this outcome allows us to predict the overall ZR system Marx generator reliability at the expected lower operating voltages of about 85 to 90 kV.