Improved version of surface plasma negative ion source

Abstract

The best features of two independently developed surface-plasma negative ion sources with separated function (independently controlled plasma generation and negative ion emission), have been combined in an optimized configuration; as a result, we propose to add a new mode of operation that will allow a 50-fold reduction in the negative ion temperature. The process of Cs injection developed for the semiplanotron negative ion source at the Budker Institute of Nuclear Physics (BINP), Novosibirsk, along with the hot cathode, first anode configuration and neutral gas injection of the ion source development at Oak Ridge National Laboratory, combines the best features of both for the continuous wave (CW) high-density, low-pressure generation of negative ions. Converter-generated cw negative ion densities of 750 mA/cm/sup 2/ are expected from the existing data base. These ions are generated with a temperature of about 7 eV; focusing these ions by a factor of 5 increases the current density to 3500 mA/cm/sup 2/ (with some mutual neutralization loss included). The ion temperature becomes 50 eV; however, according to Liouville's theorem, the brightness of the beam remains at a value of 100 mA/cm/sup 2/ eV (Volume ion sources with a cw current per channel of 100 mA, have a brightness one-third this value.) The configuration of the source geometry and atomic gas control is optimized for maximum charge exchange reduction of the ion temperature by a factor of 50. The configuration involves appropriate shaping of the converter, anode slot, and hot cathode use of a supersonic gas jet of HO, and pumping the jet into the source. Increasing the beam brightness to 1000 mA/cm/sup 2/ eV corrects for a factor of four loss in recovery of charge-exchanged ions. The concept proposed here results in a net cw brightness increase of 10, which is about 30-times greater than that otherwise available.