The effect of a steady azimuthal field on rotating magnetic field current drive

Abstract

The method of generating steady azimuthal currents in a cylindrical plasma column by means of a rotating magnetic field is investigated numerically and analytically for the case where an external steady azimuthal magnetic field is applied to the plasma. For a plasma of low resistivity, the effect of imposing a strong azimuthal field is a substantial reduction in the amount of current that can be driven. For a resistive plasma the effect is more complicated. In some cases the azimuthal field enhances current drive as has been observed in recent experiments.

Small aspect ratio tokamak configurations generated by rotating magnetic field current drive

“…This led to the more detailed experimental investigation of the RF components as outlined in Section 4. In the light of these experimental results, the existing theory of RMF current drive has been re-examined and extended to include a steady TF [17]. This modified theory agrees qualitatively with many of the experimental observations reported here.…”

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)

“…This application is a straightforward example of the ͗j ϫb͘ mechanism in action and has been the subject of numerous publications. [10][11][12][13][14][15][16][17][18][19] The applied rotating magnetic field induces an Ẽ z electric field. If we first consider a situation in which the influence of the resistive term in Eq.…”

Rotating magnetic field current drive in a hollow plasma column with a steady toroidal field

“…Experimental measurements in rotamaks with a steady toroidal field 3 and theoretical calculations in infinitely long plasma columns, also with a steady toroidal field, 9,10 have shown the existence of poloidal currents in the former and axial currents in the later, which are generally diamagnetic. We studied this issue for the two conditions indicated above.…”

“…Previous theoretical studies in configurations with a steady toroidal field 9,10 assumed that in steady state the timedependent part of all physical quantities can be described using only the first Fourier harmonic. To check this approximation we investigated the dependence of A and B with respect to Ϫ, in steady state.…”

“…8 Theoretical studies in configurations with a steady toroidal field have been limited to the calculation of steady state solutions for cylindrical plasma columns having an infinitely thin wire that carries a steady longitudinal current along the symmetry axis. 9,10 These studies assumed that, in steady state, the time-dependent part of all physical quantities can be represented using only the first Fourier harmonic ͓exp͕i(Ϫt)͖, where is the frequency of the rotating magnetic field͔. Solving the resulting set of nonlinear equations, which depends on a limited number of parameters such as resistivity, driving magnetic field, and external longitudinal current, Bertram 9 and Watterson 10 showed the possibility of driving a significant amount of current in the azimuthal direction.…”