Rotating Plasma Experiments in the B-3 Stellarator

A radial electric field can be imposed on the plasma column of a stellarator by means of a comparatively large, positively biased Langmuir probe. Measurements are presented which confirm the theoretical description of the resulting E × B rotation in terms of a leaky plasma capacitor; the leakage is caused most likely by resonant charge exchange collisions with neutral atoms. The plasma loss rate is changed in the rotating region; a decrease in loss rate by a factor 8 can be realized; too large a rotational velocity causes the loss rate to increase again. Comparisons are made with other experiments and theories. The experiments were carried out in highly ionized hydrogen and deuterium plasmas created by Ohmic heating in the B-3 stellarator, having electron temperatures of 3 to 5 eV, densities of 2 to 20 × 1012 cm−3, and confined in magnetic fields of 25 to 40 kG. An experimental justification for the interpretation of Langmuir probe characteristics under these conditions is given.