Measurement of the H- thermal energy in a volume ion source plasma

Abstract

The H- negative ion thermal energy measured using the two-laser-pulse photodetachment technique is reported to be in the range from 0.1 to 0.7 eV for various conditions of volume ion source operation (pressure-from 2 to 7 mTorr, discharge current-from 1.5 to 20 A). The hydrogen pressure has a significant effect in lowering the negative ion temperature, while the increase of the discharge current leads to a rise in T-. It is found that T- is a fraction of the electron temperature, T e. This fraction is strongly dependent on the gas pressure. T - scales linearly with the electron temperature and exceeds the highest values predicted by the theory of dissociative attachment. The possible mechanisms for H- ion heating are discussed.