Measurements of the oscillating fields and the time-averaged forces in rotating magnetic field current drive

Measurement of the RF (radio-frequency) magnetic field about the equatorial plane of the rotamak has enabled the distribution of the oscillating currents to be derived. The time-averaged forces, produced by the interaction of these currents with the oscillating field, have been estimated. In the standard field-reversed configuration there is a radial force, which helps to confine the plasma pressure, and a toroidal force, which drives the equilibrium current. In compact tokamak configurations there is an additional poloidal force, which produces a diamagnetic current. As the toroidal field increases, penetration of the RF fields improves owing to the excitation of a whistler wave mode. The connection between the rotating magnetic field technique and fast wave current drive is explained.