Driven, steady-state RFP computations

A 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 Alfven 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. (author)