Radial electric field during dynamic processes in a tokamak and L-H transitions

Expressions for the radial electric field in tokamaks are derived with allo wance for an additional contribution of the longitudinal electron viscosity (or the associated Ware drift). It is shown that, in transient processes d uring which the toroidal electric field at the plasma edge increases, the a dditional electric field can become rather strong. An increase in the shear of the poloidal plasma rotation can trigger the GH transition. That the ex perimentally observed transitions to an improved confinement mode can be as cribed to this effect is illustrated by simulating discharges in the curren t ramp-up experiments in the Tuman-3M tokamak. (C) 2001 MAIK " Nauka/Interp eriodica ".