Extraction of negative lithium ions from a lithium-containing hydrogen plasma

Negative lithium ions (Li-) were extracted from a 6-cm-diam 7-cm-long negative hydrogen ion (H-) source to simulate the condition of Li- extraction from a Li vapor introduced ion source for the neutral beam heating. The amount of the Li- current extracted from a hydrogen plasma with Li vapor was comparable to that extracted from a pure Li plasma. However, the amount of the H- current decreased as the H2 gas pressure in the source decreased due to a getter-pump effect of Li during the introduction of Li vapor. A heat shield installed to keep a high wall temperature was effective in mitigating the pressure decrease. However, the H- current extracted from the ion source equipped with the heat shield became 20% of the original value, as Li vapor was injected into the ion source. copyright 1996 American Institute of Physics