HIGH-REPETITION-RATE HYDROGEN SPARK GAP

The Naval Surface Warfare Center has been studying the recovery of pressurized spark-gap switches for several years. A two-pulse technique has been used in which the first pulse breaks down the gap and the second is used to determine recovery. For an unblown spark gap triggered near self-break, typical recovery times are about 10 ms for most gases such as air, nitrogen, and SF6. We have found that using hydrogen gas, with its high thermal diffusivity, allows the recovery time to be an order of magnitude faster, or about 1 ms. Recovery of the switch can be made even faster by triggering the switch well below self-break. Recovery time can be decreased by making the operating voltage significantly less than the dc breakdown voltage, allowing voltage to be re-applied while the gas is still hot. Tests with hydrogen have shown that recovery times (to the operating voltage) can be further reduced an order of magnitude when the gap is undervolted by approximately 50%. Recent tests have demonstrated, for the first time, 100-mu-s recovery of an unblown spark gap using high-pressure hydrogen in a trigatron configuration. Tests were performed in 1987 at 120 kV, 200 A, at 5 J of energy. In 1988 recovery was demonstrated at 60 kV, 35 kA, 200 J using a 200-ns pulse-forming line where voltage was re-applied in a 1-cos waveform (resonant charge) during the entire recovery period. In 1989 recovery at high energies was demonstrated at 50 kV, 170 kA, 12.5 kJ with 15-mu-s pulses. Plans are underway to test the switch at 600 kV.