Recovery of a weakly magnetized negative-ion plasma after photodetachment

The experimental investigation of the negative-ion recovery after photodetachment was effected using the two-laser-beam technique in the neighborhood of the extraction opening of a negative-ion source, a weakly magnetized plasma region limited by a positively biased plasma electrode. It was found that the application of a positive bias to the plasma electrode reduces the recovery time. This quicker recovery was attributed to the presence in the plasma of a directed negative-ion flow, crossing the laser channel, whose velocity increases as the positive bias of the plasma electrode is increased. The choice of a self-similar variable allows the negative-ion flow velocity to be determined from the shift of the experimental recovery curves, and the negative-ion temperature from the initial phase of the recovery. As expected, increasing the plasma electrode positive bias does not change the negative-ion temperature. copyright 1997 The American Physical Society