Central electron temperature enhancements due to sawtooth stabilization during counter electron cyclotron current drive in Tokamak a Configuration Variable

In the Tokamak a Configuration Variable (TCV), the central electron temperature obtained in discharges with counter (CNTR) electron cyclotron current drive (ECCD) is larger than with CO-ECCD or electron cyclotron resonance heating (ECRH) alone. Comparison of experimental results with calculations by the transport code PRETOR [IAEA Technical Conference on Advances in Simulation and Models of Thermonuclear Plasmas. Montreal 142 (International Atomic Energy Agency, Vienna 1992)] indicates that sawtooth stabilization is responsible for the increased confinement time and the attendant twofold enhancement of the central temperature. Sawtooth stabilization is caused in turn by the central safety factor q(0) rising above 1 for CNTR-ECCD; by contrast, the simulation results show that q(0)< 1 in the sawtoothing CO-ECCD and ECRH cases. (C) 2000 American Institute of Physics. [S1070-664X(00)03907-0].