Experimental characterization of a laser-triggered spark-gap switch

Summary form only given. We have developed an experimental test bed to characterize the performance of a laser-triggered spark-gap switch, particularly as it transitions from photoionization to current conduction. The switch is triggered by a focused 532-nm wavelength beam from a Q-switched Nd:YAG laser with a pulse duration of about 10 ns. The trigger pulse is delivered along the longitudinal axis of the switch, and the focal spot can be placed anywhere along the 5-mm, gas-insulated gap between the switch electrodes. Laser-triggered discharges consisting of pulses with as much as 15 kV across the switch and 4 kA of current through it have been obtained. The discharge through the switch is driven using an underdamped circuit that generates pulses lasting about 500 ns. The test bed is designed to support a variety of working gases (e.g., Ar, N
₂
, He, H
₂
) over a range of pressures. Electrical and optical diagnostics are used to measure switch performance as a function of parameters such as charge voltage, trigger pulse energy, insulating gas pressure, and gas species. Among these diagnostics is a two-color (532-nm and 1064-nm wavelengths) Mach-Zehnder imaging interferometer system in which the probe beams propagate transverse to the longitudinal axis of the switch, along which the current flows. The interferometer will be used to simultaneously measure plasma free electron and neutral gas densities profiles within the switch gap at different points in time during the discharge. Experimental results obtained to date will be presented. Data from our experiments will be used to determine the minimum conditions necessary to induce breakdown and conduction of a gas-insulated electrode gap in the presence of laser-induced photoionization. The electromagnetic particle-in-cell code ICEPIC will be used to produce numerical simulations of the laser-initiated arc discharge, and the experimental data will be used to validate the calculations.