Electric-field enhancement and ion-flux focusing at the multiwire cathode of a high-current plasma-filled diode

The time evolution of an unsteady ion sheath in the presence of cylindrical protrusions at the cathode is studied numerically in a two-dimensional model. The calculations demonstrate the enhancement of the electric field and the focusing of the ion flow at the protrusion vertices. It is shown that, in the stage of the sheath formation, in addition to the electrostatic focusing of the ion flux, there is also focusing caused by the curvature of the plasma boundary around a protrusion. The results of calculations agree satisfactorily with the experimental data on the delay time of explosive emission at the multi-wire cathode of a high-current plasma-filled diode. For the case of planar cathode, the analytical formulas for maximum values of electric field strength and ion current density are obtained.