Numerical calculation of radial Er profiles in H-mode tokamak discharges based on a revised neoclassical theory

The radial electric field Er and the parallel B→ center-of-mass velocity Uparallel are calculated for a simple two-component plasma. This is done by combining the global ambipolarity constraint, based on the toroidal ion angular momentum equation, with the B-weighted parallel ion momentum equation describing the work of the parallel ion forces on the plasma flow. The radial density and temperature profiles are prescribed and appropriate boundary conditions introduced for Er at the separatrix and Uparallel at the edge-core interface. It turns out that, when evaluating the governing equations within the revised nc theory for a collision-dominated pure hydrogen plasma and an electron Boltzmann equilibrium parallel B→, co-directed neutral beam injection (with respect to the induced electric current) is required to reproduce the measured radial Er profile shape with a pronounced sharp minimum at the plasma edge: either by imposing a corresponding boundary condition for Uparallel in connection with rather high particle recycling, or (narrower to the experimental situation) by including additionally a loss-cone current of energetic ions in the keV range, in connection with low particle recycling consistent with a particle transport barrier