Effect of asymmetric sources on tokamak neoclassical transport in the plateau regime

A plasma source is present in the edge of tokamak plasmas that can modify neoclassical flows and fluxes, including the self-consistent value of the electric field. The usual neoclassical assumption of divergenceless flows yields well-known equilibrium rotation rates; equilibrium rotation in the presence of sources, however, can be very different. In order to study this problem when toroidal symmetry is broken a kinetic approach is necessary. Estimates from TEXT [Nucl. Technol./Fusion 1, 479 (1981)] indicate that the source term in the drift kinetic equation is of the same order as the guiding center drift frequency. The drift kinetic equation is solved in the plateau regime with toroidally and poloidally localized sources. A modification of the radial and parallel neoclassical flows is obtained. Possible implications for L–H transitions are studied.