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 vxb 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