On the origin of superthermal electrons in the edge of RFP plasmas

This paper shows that the superthermal electron tail observed at the edge of plasmas confined in reversed field pinch (RFP) configuration can be explained as the distortion of the distribution function due to the dynamo electric field. To support this view, the distribution function has been simulated with a 2D Fokker-Planck code. The results show that both the slope of the tail of the distribution function and the asymmetry of the energy fluxes with respect to the direction of the local magnetic field can be reproduced with reasonable values of the dynamo field. To support our view, we present a detailed comparison of code predictions with measurements made in the edge region of the RFX experiment.