Ion Beam Extraction from Large Bore 11 to 13 GHz ECR Ion Source with a Pair of Cylindrically Comb-Shaped Magnetic Fields

Abstract

We have developed a large bore electron cyclotron resonance (ECR) ion source with cylindrically comb‐shaped magnetic field configuration to realize high current density and comparatively large bore ion beam which can be used for beam processes under low pressure and low microwave power. It is found that the plasma confinement of cylindrically comb‐shaped magnetic fields is more effective than that of simple multipole magnetic fields. We have constructed a large bore ion beam extractor and set to the ECR ion source. The electron density attained to 1017∼18 m−3 order, ion saturation current density is about 80∼100 A/m2 under low pressure 0.03 Pa and low microwave power 200 W. We conduct the first trial of ion beam extraction from the ECR ion source. We investigate the ion beam characteristics for extraction voltages and Ar gas pressures. The extracted ion beam current increases in proportion to extraction voltages, however at present the beam current is lower than those estimated from ion saturation current. We observed the self‐similar distribution of the extracted ion beam which is comparatively large bore. We are now investigating the ion beam extraction and going to optimize the electrode gap, the electrode position and shape of multi‐holes of the extractor.