Investigation of the mechanism of electron current suppression in an ion diode with magnetic self - insulation

Abstract

The results of a study of the generation of a pulsed ion beam of gigawatt power formed by a diode with an explosive-emission potential electrode in a mode of magnetic self-insulation are presented. The studies were conducted at the TEMP-4M ion accelerator set in double pulse formation mode: the first pulse was negative (300–500 ns and 100–150 kV) and the second positive (150 ns, 250–300 kV). The ion current density was 20–40 A/cm2; the beam composition was protons and carbon (70%) ions. It was shown that plasma is effectively formed over the entire working surface of the graphite potential electrode. During the ion beam generation a condition of magnetic cutoff of electrons along the entire length of the diode (B/Bcr ≥ 4) is fulfilled. Because of the high drift rate the residence time of the electrons and protons in the anode-cathode gap is 3‒5 ns, while for the C+ ions it is more than 8 ns. This denotes low efficiency of magnetic self-insulation in a diode of such a design. At the same time it has been experimentally observed that during the generation of ion current (second pulse) the electronic component of the total current is suppressed by a factor of 1.5–2 for a strip diode with plane and focusing geometry. A new model of the effect of limiting the electron emission explaining the decrease in the electronic component of the total current in a diode with magnetic self-insulation is proposed.