Efficient production of H- in high-density helicon plasmas

This paper describes the machanism of efficient H- production in a high-density hydrogen plasma produced by helicon wave discharge. An H- source using helicon wave discharge has been developed. Spatial and temporal variations of H- density in the helicon plasma were measured by laser photodetachment technique. A steep increase in H- density was observed in the afterglow. The H- ions were efficiently produced for the first 20 mu s after the termination of the discharge and mainly lost by mutual neutralization with positive ions. In the outer region of the plasma column, 20% of the negatively charged particles were H- ions. In the region of T-e=1.5-2 eV, the effective attachment rate coefficient defined as the average value for hydrogen molecules of all energy levels was evaluated to be 0.5-1.3x10(-11) cm(3)/s, of which the value is 3-order higher than that for attachment to the v = 0 level of the ground state molecules.