Stabilization of ion beam generation in a diode with self-magnetic insulation in double-pulse mode

Abstract

The paper presents the results of statistical studies of ion beam generation in different geometry diodes with explosive emission cathode in a mode of self-magnetic insulation. The experiments were carried out using the TEMP-4M pulsed ion beam accelerator during its operation in both unipolar pulse mode (100 ns, 250–300 kV) and bipolar-pulse mode with the first negative (300–600 ns, 100–150 kV) followed by a second positive (120 ns, 250–300 kV) pulse. It is found that the standard deviation of the total energy and energy density of the beam does not exceed 10–11%, while the same shot-to-shot variation in ion current density was found to be 20–30%. The mechanism of the energy density stabilization from pulse to pulse may be associated with the charge exchange between accelerated ions and stationary molecules and formation of accelerated neutrals. We observed a high correlation between the energy density (or total beam energy) and the duration of the first voltage pulse. We performed analysis of Blumlein statistical performance when the Blumlein was terminated with a resistive load and with a self-magnetically insulated ion diode. A characteristic feature of Blumlein operation in the double-pulse mode is an excellent reproducibility of breakdown of the preliminary spark gap, the variation in breakdown voltage is <2%. At the same time, the shot-to-shot variation in the breakdown voltage of the main spark gap in both bipolar- and unipolar pulse mode is 3–4 times higher than that for the preliminary spark gap. To improve the statistical performance of the main spark gap we used the first voltage pulse at the output of Blumlein to trigger the main spark gap. The new trigatron-type regime of the main spark gap operation showed a better reproducibility of the first pulse duration, with the time jitter not exceeding 10 ns in a set of 50 pulses.