BOUNDARY-LAYER CALCULATIONS FOR TOKAMAKS WITH TOROIDAL LIMITER

The calculations with the 2D boundary layer code SOLXY originally restricted tokamaks with a poloidal limiter have now been modified to describe also the plasma edge of a toroidal belt limiter like the ALT-II of TEXTOR. We have selfconsistently included and investigated the influence of the electric and pressure gradient drifts and electric currents comprising both the perpendicular and the radial drift flows v-perpendicular-to, v(rd), j-perpendicular-to, j(r). The numerical results show qualitative agreement with experimentally observed edge profiles of electron density and temperature as well as particle fluxes to the limiter. They not only verify the poloidal asymmetries between electron and ion side of the limiter in standard Ohmic discharges, but also recover the changes in these asymmetries when simultaneously reversing the orientations of the toroidal magnetic field and the plasma current. We work out the crucial physical role of the limiter reaction to the drift motions, combined with the poloidally varying particle and energy outflux from the core into the sol, for explaining the measured phenomena. The code-calculated profiles are discussed in detail for selected parameter sets.