Plasma resistivity in the presence of a reversed-field pinch dynamo

A global calculation of reversed-field pinch (RFP) plasma resistivities, ηw∥ and ηk∥, based on power balance and magnetic helicity balance, respectively, is discussed. For reasonable RFP beta values (β<0.1), ηk∥ provides an estimate of plasma resistivity parallel to the magnetic field, and agrees with the Spitzer resistivity within a factor of two. The expression (1−ηk∥/ηw∥) indictes the fraction of ohmic heating power absorbed by fluctuations in the discharge. An examination of 180 kA discharges on the Los Alamos ZT-40M experiment suggests that approximately one-third of the ohmic heating power drives fluctuations, including the dynamo effect, during discharge sustainment.