Modelling the magnetic field of the acceleration channel End-Hall ion source

Abstract

In recent decades, the End-Hall ion sources have been used in the optical coating industry for ion-assisted deposition and surface pre-cleaning operations e.g. /1, 2/. The employ of gridless ion sources based on magnetoplasmadynamic thrusters and Hall effect has been beneficial for many applications, because they have a relatively high ion flux density, wide spatial distribution, moderate beam energy levels of approximately 60-200 eV, and its ability to handle either inert or reactive gases. However, as modern manufacturing processes scale to larger systems, higher rates, and larger substrate areas, it has become necessary to increase power capacity of the End-Hall ion sources, reduce form-factor sand significantly improve their service ability and maintenance requirements and, thereby, reduce cost of ownership. In Hall-effect ion sources, the magnetic field B is perpendicular to the discharge current forms a barrier to electron transport from the cathode to the anode at a specific location in space, leading to the increase of the electric field E in the plasma at that location, in a direction perpendicular to the magnetic field. This electric field accelerates ions away from the source. The resulting cross-field configuration generates a current (the Hall current) that direction is perpendicular to the E×B fields e.g /3, 4/. Most Hall-effect ion sources have an axially symmetric design in which the applied magnetic field and the resulting electric field are such that the Hall current is generate in the azimuthal direction. In this configuration, the anode is at the end of the channel and the exhaust (and acceleration region) is at the other end. In the End-Hall ion configuration, the anode has a conical shape, the acceleration region is close to the anode surface, and the beam divergence is larger.