Comparison of H− and D− production in a magnetically filtered multicusp source

Abstract

A JAERI (Japan Atomic Energy Research Institute)negative ion source was tested at LBL (Lawrence Berkeley Laboratory) as part of the U.S.–Japan Fusion Cooperation Program. By varying the strength of the magnetic filter from 450 to 930 G cm, we compared production, transport, and extraction of the negative ions. The maximum current densities, which were obtained at the corresponding optimum filter strength for each gas species, were 10.4 mA/cm2 for H− and 8.4 mA/cm2 for D− at arc discharges of 40 kW. The ratio of the ion current densities (JD−/JH−) is about 0.8, which is higher than 1/(2)1/2 . The electron to negative ion ratio was 13 for hydrogen and 38 for deuterium at the corresponding optimum filter strength. The higher ratio in deuterium is probably due to higher space potential of deuterium plasma by a few volts.