Development of the directional Langmuir probe for the charged particle flow measurement

The extraction mechanism of negative ion beams is affected by the behavior of positive and negative ions near the extraction apertures. Flow of the charged particles in a hydrogen discharge were measured with a newly developed directional photodetachment probe which has a single probe tip. Compared with our previous multiple-tip directional probe, the single-tip directional probe was able to measure fine flow structure of the positive and the negative ions without spatial ambiguity associated with electron deflection magnetic field and density gradient. The single-tip probe observed the turning of the flow of the negative hydrogen ion by increasing the bias voltage in the extraction region of the negative ion source.