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 equati on in three dimensions (two dimensions in velocity space and one dimen sion in real space). To this end, a Fokker-Planck code has been develo ped, including Coulomb collisions, direct current (dc) electric field, radial diffusion due to magnetic turbulence, ambipolar electric field s, 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 o f fast electrons associated with stochastic magnetic fields might be a ble to sustain the reversed field configuration. Quantitatively, it is found that the level of magnetic turbulence necessary to obtain the t oroidal field reversal at the plasma edge is compatible with levels ty pically measured in reversed field pinch devices. In particular, the m ain parameters of standard discharges in the largest existing facility of this type, RFX (reversed field experiment) [Proceedings of the 14t h Conference on Plasma Physics and Controlled Nuclear Fusion Research, Wurzburg, 1992 (International Atomic Energy Agency, Vienna, 1993), Vo l. 2, p. 583], have been successfully simulated.