Stochastic magnetic and ambipolar electric fields in the plasma edge region of RFX

Abstract

The edge region of the reversed field pinch experiment RFX has been investigated with Langmuir and calorimetric probes. The energy flux measurements reveal a spatial structure that is consistent with the presence of a superthermal tail in the energy distribution function of the electrons, as expected according to the kinetic dynamo theory (KDT). In the framework of this model, the value of the magnetic field line diffusion coefficient in the edge region has been derived. The radial electric field obtained from the plasma potential gradient is opposite in sign to the ambipolar electric field expected in a stochastic magnetic field. The discrepancy is discussed in terms of particle recycling at the wall.