Resistive interchange modes in reversed-field pinches

A new regime is found in which the growth rate of the resistive interchange mode in cylindrical geometry is considerably smaller than previously believed. This stabilization is due to coupling to the external, tearing stable, region. Considering the crossover point from the conventional resistive interchange to the new regime as a critical beta, βc, it is found that βc∼7% for classical resistivity with Te = 10 eV, in agreement with recent numerical studies. However, βc scales as T−3/5e, giving βc∼1% for Tc = 1 keV. Marginally stable pressure profiles for totally localized modes in the Bessel function model for a reversed-field pinch are also computed, and show that for tearing stable equilibria the central pressure may be up to 400 times the pressure at the wall.