Nonlinear reversed-field pinch dynamics with nonideal boundaries

The nonlinear behavior of the reversed-field pinch bounded by a resistive shell or a distant conducting wall is investigated with a three-dimensional magnetohydrodynamic code. Nonlinear interaction between modes enhances fluctuation levels as the conducting wall is removed. The enhanced fluctuation induced v×b electric field, which produces the dynamo effect, suppresses toroidal current, and enhances surface helicity dissipation. Thus, loop voltage must increase to sustain the current and maintain helicity balance.