Two-Dimensional Pic Simulation of Spark Gaps with Longitudinal Magnetic Fields

We have performed two-dimensional, relativistic, particle-in-cell simulations of low-pressure, argon-filled, spark-gap closing switches in the presence of an external longitudinal magnetic field. This study has been confined to a relatively low pressure range (0.01-1 Torr). Two different issues have been examined. The first is the variation of breakdown voltage with magnetic field for switches operating in the Townsend discharge regime. The second is the variation of current risetime with the field - this study is done in a different parameter range as compared to the breakdown study. We find that both the breakdown voltage and current risetime are sensitive functions of the applied magnetic field B. For a given fill pressure, as B is increased, the breakdown voltage first decreases, passes through a minimum and then increases. The rise time shows a similar trend. The value of B corresponding to the minimum breakdown voltage tends to increase with the fill pressure.