Rimfire: a six megavolt laser-triggered gas-filled switch for PBFA II

We have developed a new multiple-stage laser-triggered SF6 spark gap, which has performed well in tests at nearly 6 megavolts and half a megampere. It has survived many hundreds of shots between 5 and 5.7 MV, the highest voltage tested. A 25 millijoule ultraviolet laser pulse arriving in its trigger gap reliably closes the whole switch in 20 nanoseconds with 0.4 ns 1-sigma jitter. The closing time has a low dependence on the applied voltage, about 0.9 ns/% of self-break voltage. For a 10 mJ laser pulse, the jitter is 1.5 ns and the slope is 1.0 ns/%. No prefires have occurred; the estimated prefire rate at 90% of self-breaking voltage is less than 0.1%. The switch inductance is 400 nanohenries, of which about 100 nh comes from the spark channels. The switch is 68 cm long and 61 cm in diameter