Observations of up-down differences in plasma response during ECRH on TCV
The Tokamak à Configuration Variable (TCV) ECW system, when complete, will provide 3 MW X2 and 1.5 MW X3 for 2s. Present electron cyclotron resonance heating (ECRH) experiments have been carried out using up to 1MW of power. Differences in sawtooth activity have been seen during magnetic field scans, plasma vertical displacement (about 20cm) and mirror launching angle scans. These differences are strongly correlated with the position of the heating relative to the inversion radius of the sawteeth. In addition, we have observed small but reproducible differences between the central electron temperature, X-ray intensity and hot ion tail temperature when heating above or below the plasma midplane. There are several possible explanations for these differences; perhaps, the most plausible is that the asymmetry in the field line geometry, due to the presence of the poloidal field, leads to a small current drive component during ECRH even at perpendicular injection. As is well known, significant differences in central temperature and sawtooth activity are often seen between CO-and COUNTER-current drive. More recently, polarization experiments during electron cyclotron current drive (ECCD) have shown that these differences exist even when a relatively small fraction of the total injected power is properly coupled to the X-mode. The TORAY ray-tracing code, providing linear ECCD efficiencies, indicates that ECCD efficiencies during perpendicular injection can approach those with low X-mode fraction and that an up-down asymmetry exists. Experimental evidence of this asymmetry will be presented and discussed.
Bibliographic Reference: Article: 1998 International Congress on Plasma Physics, 25th EPS Conference on Controlled Fusion and Plasma Physics, Prague (CZ), June 29 � July 3, 1998
Record Number: 199811268 / Last updated on: 1998-10-27
Original language: en
Available languages: en