Radial Transport Effects on Eccd in the Tcv and Diii-D Tokamaks and on Ohmic Discharges in the MST Rfp

The comprehensive CQL3D Fokker-Planck/Quasilinear simulation code has been benchmarked against experiment over a wide range of electron cyclotron conditions in the DIII-D tokamak (C.C. Petty et al., 14th Topical Conf. on RF Power in Plasmas, 2002). The same code, in disagreement with experiment, gives 560 kA of ECCD for a well documented, completely ECCD-driven, 100 kA TCV shot [O. Sauter et al, PRL, 2000]. Recent work (R.W. Harvey et al, Phys. Rev. Lett., 2002) has resolved the differences as due to radial transport at a level closely consistent with ITER scaling. Transport does not substantially affect DIII-D ECCD, but at similar ECH power has an overwhelming effect on the much smaller TCV. The transport is consistent with electrostatic-type diffusion (D_ρρ constant in velocity-space) and not with a magnetic-type diffusion (D_ρρ ∝ |v_|||).

Fokker-Planck simulation of Ohmic reversed field pinch (RFP) discharges in the MST device reveals transport velocity dependence stronger than |v_||| will give agreement with current and soft X-ray spectra in standard discharges, but in the higher confinement, current profile controlled PPCD discharges, transport is again electrostatic-like. This is consistent with the object of PPCD, which is to replace magnetic turbulence driven current with auxiliary CD to improve transport. The tokamak and high-confinement RFP results mutually reinforce the constant-in-velocity-space "electrostatic-type turbulence" conclusion. The steady-state energy and toroidal current are governed by the same radial transport equation.