Ion beam generation with inhomogeneous anode and cathode plasmas

The physical understanding of the ion beam enhancement and divergence in magnetically insulated ion sources, Bappl-diodes, for pulsed power generators is still lacking. We propose a phenomenological analytical model for the "stable" regime of operation of Bappl-diodes. The effect of rippled anode-plasma surfaces on the focusing properties of the diode is analysed. Conditions for the experimentally observed value of the microdivergence Θ ≃10–20 mrad are obtained. The effect of scattering of the electrons in the disturbed electrical fields is calculated. Its effect on the electron distribution in the magnetically insulated vacuum gap is estimated: A low level ≤1% of excitations for the “slow” and “fast” fluctuations generates enough broadening of the electron distribution. — Work is in progress to incorporate the model into the computer code BFCPIC to be used in computer experiments for designing high brightness diodes. This is a useful tool in the process of optimizing Bappl-diodes for good focusing properties. The first results on the effect of moving plasma boundaries are reported.