Ion-Emission Properties of a Plasma in a Gaseous-Ion Source with a Plasma Cathode

摘要

1. A promising scheme of sources of broad gaseous-ion beams is a two-stage electrode system involving a plasma cathode, which has a long service life, and a plasma generator with desired ion-emission characteristics such as plasma-emitter size and shape, emission-current density, and an acceptable level of emission nonuniformity. Nowadays, there are ion sources with plasma cathodes based on microwave and rf discharges, where a chamber placed in a multipole magnetic field is used in the second stage [1, 2]. Cold-cathode ion sources, where ions are extracted from the anode plasma of a glow discharge in a magnetic field, have also been designed [3]. A feature of the glow-discharge ion source described in [4] is the use of a grid separating the cathode and anode stages and the absence of a magnetic field in the second stage consisting of a hollow cathode and a thin-rod anode. Between these electrodes, gas ionization induced by injected electrons gives rise to a non-self-sustained glow discharge under low gas pressures (as low as 3 x 10~(-3) Pa). However, since the ion current is distributed over the whole surface of the second-stage cathode, the current of ions extracted from the plasma amounts to approximately 4% of the injected-electron current.