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

The physics underlying the rotating magnetic field current drive technique is presented. The rotamak is a compact torus configuration having the uniqu e and distinctive feature that the toroidal plasma current is driven in a s teady-state, noninductive fashion by means of the application of a rotating magnetic field. In its basic form, the rotamak is operated as a field-reve rsed configuration (Rotamak-FRC). However, by means of a simple modificatio n, a steady toroidal magnetic field can be added to the basic rotamak appar atus and the configuration then becomes that of a spherical tokamak (Rotama k-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 w ith input powers of 300 kW (at 0.5 MHz). Hydrogen plasmas with n(e) approxi mate to 7 x 10(18) m(-3) and T-e approximate to 35 eV have been obtained. T he noteworthy reproducibility of the rotamak discharge has enabled the magn etic field lines of an ST to be directly reconstructed from experimental da ta for the first time. Attention is drawn to the fact that a fair evaluatio n of the rotamak concept requires experimentation at higher radio-frequency power levels than are presently available. (C) 1999 American Institute of Physics. [S1070-664X(99)94705-5].