Electron sheath dynamics in magnetically insulated diodes

We have investigated the two dimensional dynamics of electron sheaths in magnetically insulated diodes with gap discontinuities, using MASK, a 2-1/2 dimensional electromagnetic, and relativistic particle simulation code. The discontinuity is represented by a step in the cathode surface. A simple theoretical description is consistent with numerical simulations. The critical applied magnetic field necessary for magnetic insulation depends strongly on the nature of the discontinuity and is observed to be a function of the size of the discontinuity, the direction of electron flow relative to the discontinuity, and the usual diode parameters. The ultimate object of this study is to determine the conditions for magnetic insulation and unsteady flow and the influence of electron flow irregularities on diode performance and beam divergence.