Abstract
Design principles and basic properties of broad-beam gas ion sources based on a low-pressure glow discharge are discussed. It is shown that properties of the discharge in a coaxial electrode structure with a hollow cathode and a rod anode in a magnetic field favor its use in sources of gas ions. Two main types of ion sources using this electrode structure are described. Application of a weak magnetic field facilitates igniting of the discharge, ensures stable running of high-current discharges under low gas pressures, and provides for formation of a homogeneous plasma. These conditions are realized in an inverted magnetron-type electrode system with ion extraction from the plasma generated in the cathode part of the discharge. The discharge with a strong magnetic field in the cathode region, which is used in a plasmatron-type electrode system with extraction of ions from the anode plasma, gives improved gas and energy efficiency of the ion source. The discharge ignition and operation conditions, ion-emission properties and mass-charge composition of the plasma, contamination of the plasma as a result of the cathode sputtering in the glow discharge, features specific to extraction of ions and beam formation by an electrostatic ion-optical system are analyzed and compared for these two structures. Glow-discharge gas ion sources generate broad ion beams with a 5–200 cm2 cross-section and an energy of 1–50 keV under pulsed and continuous regimes. The beam current density is from 10 μA/cm2 to 10 mA/cm2.
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