Limitation of the electron emission 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 and 250–300 kV). The ion current density was 20–40 A/cm2; the beam composition was protons and carbon 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+ carbon 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.