Mass-Energy Analysis of Ions Generated in the Anode Plasma of a High-Current Vacuum Spark

Abstract

This paper presents research results on the ion charge state and energy distribution in the anode plasma generated at the spark stage of a high-current vacuum discharge. The cathode and the anode are both made of liquid metal Ga–In alloy. The use of a circuit with a relatively low impedance (6 $\Omega$ ) and a small interelectrode gap $({\sim}{\rm 1}~{\rm mm})$ made it possible to obtain a relatively high discharge current $({\sim}{\rm 1}~{\rm kA})$ at an initial voltage of 10–15 kV. Therefore, an electron beam consisting of a train of pulses with a duration of 5 ns and power density of ${\sim}2.5\cdot 10^{8}~{\rm W}/{\rm cm}^{2}$ is formed in ${\sim}{\rm 50}~{\rm ns}$ , giving rise to high-density anode ablation plasma. The parameters of the ion component of this plasma are investigated with a mass energy analyzer. It is found that ions with ${\rm Z}=1\hbox{--}4$ are present in the plasma, and the ion energy increases roughly in proportion with increasing ion charge. Increasing the initial voltage causes an increase in the fraction of highly charged ions and in their energy. The absolute values of the ion energy reach ${\sim}{\rm 1}~{\rm keV}$ . Two mechanisms of ion acceleration are discussed: adiabatic expansion of the anode plasma and ion acceleration by an ambipolar electric field. It is shown that the regularities found in this paper can be explained only with resort to both mechanisms.