Characteristics of an rf plasma neutralizer

Measurements of the electron density and temperature of a high-power, rf-driven, magnetic multicusp contained plasma are presented. The plasma chamber is a shortened version of an rf plasma neutralizer design for slab H- beams; hence its ends have no cusp fields, but instead contain large openings to emulate the plasma lost through beam apertures. Data is presented from operation with hydrogen in the 1--10 mTorr range and rf power up to 60 kW. Peak electron densities of 1.2 x 1013 cm-3 and maximum degrees of ionization of 12% have been recorded. This density is sufficient for an H- plasma neutralizer; but for a significant enhancement of th neutralization efficiency over that of a gas cell, the degree of ionization must be increased. Based on these results, estimates of the power requirements of a practical rf plasma neutralizer are presented