Abstract
In reversed field pinches (RFPs), edge fast electrons play some important roles in the energy transport and RFP dynamo. There have been here detailed measurements of electron currents and floating potential with electrostatic probes at the edge region, showing that field-aligned current is carried by superthermal electrons, which results in reversed toroidal current outside the reversal surface. The time evolution of radial electric field, which is estimated from that of floating potential measured with insertable probes with some assumptions, revealed that radially outward electric field is formed in about 100 μs. Given that the radial electric field is a result of superthermal electron diffusion in a stochastic magnetic field line, then the estimated diffusion coefficient agrees well with the numerically calculated values, which were obtained by using Monte-Carlo particle orbit calculation in combination with a 3-dimentional nonlinear MHD simulation. It is concluded that the radial electric field is formed by stochastic diffusion of superthermal electrons, which also play important roles in RFP dynamo.
