RECOVERY OF A WEAKLY MAGNETIZED NEGATIVE-ION PLASMA AFTER PHOTODETACHMENT

The experimental investigation of the negative-ion recovery after phot odetachment was effected using the two-laser-beam technique in the nei ghborhood of the extraction opening of a negative-ion source, a weakly magnetized plasma region limited by a positively biased plasma electr ode. It was found that the application of a positive bias to the plasm a electrode reduces the recovery time. This quicker recovery was attri buted to the presence in the plasma of a directed negative-ion flow, c rossing the laser channel, whose velocity increases as the positive bi as of the plasma electrode is increased. The choice of a self-similar variable allows the negative-ion flow velocity to be determined from t he shift of the experimental recovery curves, and the negative-ion tem perature from the initial phase of the recovery. As expected, increasi ng the plasma electrode positive bias does not change the negative-ion temperature.