Kinetic modeling of fast electron dynamics and self-consistent magnetic fields in a reversed field pinch

The dynamics of fast electrons in a reversed field pinch configuration is investigated by numerically solving the appropriate kinetic equation in three dimensions (two dimensions in velocity space and one dimension in real space). To this end, a Fokker-Planck code has been developed, including Coulomb collisions, direct current (dc) electric field, radial diffusion due to magnetic turbulence, ambipolar electric fields, and the self-consistent evaluation of the magnetic fields generated by the plasma itself. This has allowed the theoretical validation of the kinetic dynamo model in a realistic geometry. In contrast to fluid-turbulent theories, such a model predicts that the radial diffusion of fast electrons associated with stochastic magnetic fields might be able to sustain the reversed field configuration. Quantitatively, it is found that the level of magnetic turbulence necessary to obtain the toroidal field reversal at the plasma edge is compatible with levels typically measured in reversed field pinch devices. In particular, the main parameters of standard discharges in the largest existing facility of this type, RFX (reversed field experiment) [Proceedings of the 14th Conference on Plasma Physics and Controlled Nuclear Fusion Research, Wurzburg, 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 2, p. 583], have been successfully simulated.