Driven, steady-state RFP computations

Abstract

A previously described pseudospectral three-dimensional MHD code is used to compute the dynamical behaviour of a channel of magnetofluid carrying an axial current and magnetic flux. This situation contains the essential MHD behaviour of the reversed-field-pinch (RFP). An externally imposed electric field is applied to an initially current-free magnetofluid, and drives currents that rise and eventually fluctuate about values corresponding to pinch ratios Θ ≈ 1·3, 2·2 and 4·5. A period of violent turbulence leads to an approximately force-free core, surrounded by an active MHD boundary layer that is not force-free. A steady state is reached that can apparently be sustained indefinitely (≥several hundred Alfvén transit times). The turbulence level and time variability in the steady state increase with increasing Θ. The average toroidal magnetic field at the wall reverses for the Θ ≈ 2·2 and 4·5 runs, but not for the Θ ≈ 1·3 one. Negative toroidal current filaments are observed. The Lundquist numbers are of the order of a few hundred.