Effect of parallel electric field on ion heating in RFPs.*

Strong ion heating is observed in the reversed field pinch (RFP). During a sawtooth crash in the Madison Symmetric Torus RFP the ion temperature can spontaneously double in 100 microseconds. It is also observed that high Z impurities are heated stronger than bulk ions. The possibility of ion heating due to tearing instabilities is examined. Our previous study examined the heating due to viscous damping of strongly localized perpendicular flows existing in the vicinity of resonant surface in tearing mode. Here we present the results due to the parallel electric fields in the tearing mode. We estimate the parallel electric field in the vicinity of resonant surface from the two fluid equations in which the electric field is mainly balanced by the parallel pressure gradient. The perturbed pressure profile is found from the cylindrical tearing eigenmode in resistive MHD approximation. The ion heating in the electric field with the parallel gradient is estimated from numerical solution of kinetic equation with Landau collision operator. The potential energy of high Z impurities in such a field can exceed their thermal energy, thus the effective heating is expected.