Plasma diagnostics in negative ion sources

The use of thin probes and laser photodetachment for measuring the negative ion density are described. In the photodetachment method, the work done by detecting the free electrons produced by laser-induced photodetachment is described. Several detection means for the change in electron density produced by laser-induced photodetachment are reviewed: microwave cavity, electrostatic probes and optogalvanic detection. The problems of the choice of the laser and of identification of the negative ions are also discussed. The two-laser photodetachment technique, applied for the measurement of the negative hydrogen and deuterium ion temperature, is described, as are time-resolved measurements of negative ion density.