Recovery of water switches

The recovery of a water switch has been studied by means of Schlieren diagnostics. it was found that a vapor bubble which begins to expand 2 μs after the electrical breakdown and decays after 1 ms determines the recovery time of the switch. The recovery time, defined as the time required to reach the full voltage across the gap after a previous switch event, was measured for two different electrode geometries by means of a pulse-probe (double pulse) system. The first pulse generated the water breakdown. The second pulse served as a probe pulse. The degree of recovery was defined as the ratio of the breakdown voltage obtained with the second pulse to that of the first pulse. Full recovery was achieved for a switch in static water with an energy deposition of 0.6 J per cm gap length after 2 ms corresponding to a repetition rate of 500 Hz. This rate could be increased to 1 kHz by flowing the water. An all-water pulse generator consisting of a water switch and a pulse forming network with water as dielectric was built and tested. This pulse generator produced 14 kV, 10 ns pulses into a 15 Ω load with a current rise of 4×10¹¹ A/s.