170-kV laser-triggered water switch experiments

We report the results of experiments using a small Q-switched Nd:YAG laser at 532 and 1064 nm to trigger a 170-kV pulse-charged water switch. 1-sigma jitters as low as +/- 1.7 ns were demonstrated; an order of magnitude improvement over the +/- 25-ns jitter of the switch in its self-breaking mode. At the optimum observed triggering wavelength of 532 nm, a 7-ns laser pulse gave better results than a 0.15-ns laser pulse. Time resolved optical diagnostics suggest a multistage triggering process in which the laser forms a string of point plasmas between the switch electrodes. These point plasmas expand, cool and merge, forming a vapor column between the electrodes that breaks down rapidly with low jitter.