WALL EFFECTS ON ELECTRON DYNAMICS IN THE SOL

In a tokamak divertor, steep gradients in the density and temperature profiles are usually established with a scale length that is often sho rter than the mean-free path of energetic electrons. The electron flux is then non-local in nature, being determined not only by local densi ty and temperature gradients but by integrals of these quantities over an extended region in space. In the present work, such non-local expr essions for the electron particle and heat fluxes are derived, general izing earlier work to include the effects of walls bounding the plasma . The results are found to be in excellent agreement with a numerical solution of the full kinetic equation, if the temperature falls off ra pidly near the wall. In the opposite limit df a nearly isothermal plas ma, a comparison with a variational calculation of the particle flux i s presented, showing less satisfying agreement.