Generation of High-Intensity Aluminum-Ion Beams at Low Energy

Abstract

High-intensity repetitively pulsed beams of low-energy aluminum ions are generated in experiments. A continuous vacuum–arc discharge is used as a generator of metal plasma. Aluminum-ion beams with a current density of up to 0.47 A/cm2 are generated owing to the plasma immersion extraction of ions with subsequent ballistic focusing in the drift space of potential electrodes. Regularities of the generation of high-intensity ion beams are studied at a pulse repetition rate of 105 pulses per second versus bias voltage ranging from 1.2 to 3 kV, pulse duration ranging from 2 to 8 μs, and residual gas pressure. Transport efficiency and beam focusing are determined by the conditions for neutralization of the space charge. Even under complete filling of the drift space with preliminary injected plasma, the conditions for neutralization of space charge are dynamically varied due to an increase in the space charge upon ballistic focusing. Experimental results are presented to prove formation of a virtual anode under conditions for insufficient plasma injection in the drift space of the beam. It is shown that the transport efficiency of the high-intensity beam may substantially be increased in the presence of argon in the experimental chamber.