The anomalous diffusion of the current sheath in a toroidal discharge

Abstract

The diffusion of the current sheath in ZETA is shown to be incompatible with classical resistive diffusion at high rates of energy input or low pressures. In the anomalous region the diffusion time is approximately proportional to mass density and inversely proportional to the applied electric field. There are considerable asymmetries in the toroidal discharge and complicated convective motions during the diffusion phase, but these appear not to be the primary cause of the enhanced diffusion. Evidence has been obtained that the enhanced diffusion is not due to the presence of a probe in the plasma. It is therefore probable that there must be an enhanced resistivity, depending on the local values of mass density and electric field, which is presumably due to some form of turbulence, but none of the simple models of such turbulence considered account for the results.