Toroidal drift of a collisionless plasma

The toroidal drift of a collisionless plasma flowing along a curved magnetic field has been directly observed. The experiment was done using a low density plasma generated in a small single-ended Q machine. The magnetic lines were bent into an arc of a circle with curvature adjustable by additional magnetic windings, designed for smooth line curvature with the aid of a stereoscopic computer-graphics device; the magnetic geometry was also determined by a weak electron beam. The polarization field in the plasma was short-circuited by the presence of the hot ionizer which terminated one end of the plasma. The toroidal drift was observed experimentally by a movable battery of 45 probe wires mounted in an insulator which terminated the other end of the plasma. The plasma potential and plasma density were measured with this and displayed quantitatively using a fast analog-digital data printer. The experimental data correlated satisfactorily with a two-fluid theory in which the curvature drift was modeled by an effective gravitational force.