A review of rotating magnetic field current drive and the operation of the rotamak as a field-reversed configuration (Rotamak-FRC) and a spherical tokamak (Rotamak-ST)

Abstract

The physics underlying the rotating magnetic field current drive technique is presented. The rotamak is a compact torus configuration having the unique and distinctive feature that the toroidal plasma current is driven in a steady-state, noninductive fashion by means of the application of a rotating magnetic field. In its basic form, the rotamak is operated as a field-reversed configuration (Rotamak-FRC). However, by means of a simple modification, a steady toroidal magnetic field can be added to the basic rotamak apparatus and the configuration then becomes that of a spherical tokamak (Rotamak-ST). The performance of a 50-liter rotamak device, both as an FRC and as an ST, is described. Toroidal currents of over 10.5 kA have been achieved with input powers of 300 kW (at 0.5 MHz). Hydrogen plasmas with ne≈7×1018 m−3 and Te≈35 eV have been obtained. The noteworthy reproducibility of the rotamak discharge has enabled the magnetic field lines of an ST to be directly reconstructed from experimental data for the first time. Attention is drawn to the fact that a fair evaluation of the rotamak concept requires experimentation at higher radio-frequency power levels than are presently available.