On nonquasineutrality and turbulent heat transfer in a tokamak

A new approach is proposed for describing a steady turbulent state formed far from thermodynamic equilibrium in the plasma column of a tokamak as a result of the development of microinstabilities. A fundamental feature of such a highly nonequilibrium plasma is its nonquasineutrality, i.e., the plasma properties are largely determined by electric fields localized on a scale of the order of the Debye radius. It is established that the transverse thermal diffusivity is determined by the expression where U is the voltage per orbit of the tokamak. The relation n(r)q(r)5=const and the increase in thermal diffusivity at the periphery of the plasma column can be explained on the basis of the proposed approach. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 640–645 (10 May 1998)