Behavior of Negative Hydrogen Ion and its Beam by Bias and Beam Extraction Voltages

Negative hydrogen ion (H-) dynamics from production to beam extraction in H- source for fusion have not been enough understood in cesium-seeded negative-hydrogen-ion sources. This dynamics understanding contributes constructions of higher performance ion sources. The H- is produced on and emitted from plasma grid electrode (PG) which is boundary electrode between source plasma and beam. The H- density in the vicinity of the PG decreased with bias voltage (between PG and arc chamber) by suppression of H- emission and/or yield. The H- density decrement was observed in H- beam extraction phase and penetrated to 30 mm depth from PG. The depth and H- beam current decreased with bias voltage. One of the possibilities which explain it is extracted H- coming from space in the vicinity of the PG. An object made of ceramic was inserted above the PG aperture. The H- beam intensity decreased if the object was set 9 mm from PG. This does not conflict with the possibility.