Kinetic effects of magnetic turbulence in tokamaks

The electron kinetic theory of tokamak plasmas in the presence of magnetic turbulence is investigated. The evolution of the electron distribution function under the effect of turbulent magnetic fields, a DC electric field and Coulomb collisions is governed by a 3-D kinetic equation (2-D in velocity space and 1-D in ordinary space). The turbulence is described by a radial diffusion operator, coupled to slowing down in energy due to ambipolar fields. The resulting kinetic equation is solved numerically, by means of a new fully 3-D Fokker-Planck code. It is shown that in a turbulent plasma the central equilibrium electron distribution function is nearly Maxwellian, but in the temperature gradient region an anisotropic superthermal tail develops owing to radial diffusion of hot electrons. This affects the local electrical conductivity and the global plasma resistance. An analytical expression of this turbulent electrical conductivity is derived. (author). 31 refs, 11 figs