Effects of mixing low-Z gases on a 2.45-GHz multiply charged ion source

Fundamental phenomena in mixing low-Z gases into the operating gas have been experimentally studied in an electron cyclotron resonance (ECR) multicharged ion source (2.45 GHz). The ECR plasma is confined in the mirror held superimposed by the octupole magnetic field. An ECR zone is formed near the bottom of the mirror trap. The main operating gas is argon. Hydrogen, helium, nitrogen, and oxygen gases are chosen as admixtures. The multicharged ions pass through the extractor at the mirror end, and the charge state distributions are investigated at various pressures and mixing ratios. The gas-mixing effect enhances production efficiency of high-charge state ions (Ar/sup 6+-9+/); in particular their currents substantially increase in the case of oxygen mixing. There exists an optimum mixing ratio and total pressure for each admixture. The electron temperature and density are measured by a Langmuir probe. The cause of enhanced production by admixing low-Z gases is discussed by taking account of plasma parameters including plasma potentials and ion temperatures estimated from elaborate measurement of the ion beam.