Plasma Rotation Across the H-mode Transition in TCV
The variation of plasma poloidal rotation across an Ohmic H-mode transition has been measured using from the Doppler shift of visible radiation from intrinsic impurities. Using a 1m Cz-erny-Turner spectrometer with an OMA III detector a 2.5ms time resolution was achieved with a sensitivity to plasma rotation of better than 0.5km/s. The measurement was simultaneously performed for CIII radiation and CV radiation corresponding to the region around and inside the last closed flux surface respectively. There is a clear difference in the behaviour of the radiation from these species across the transition. CIII shows a 75% drop in intensity, a 2km/s jump in toroidal rotation velocity and a ~50% increase in ion temperature. CV shows little intensity change across the transition, a 10km/s jump in the poloidal rotation velocity and a ~130% increase in the ion temperature. These values, combined with estimations of the ion pressure profiles result in an estimated radial electric field of ~10kV/m just inside the last closed flux surface. Although the time resolution does not permit a clear identification, there is evidence that the poloidal velocity change actually precedes the H-mode transition, suggesting that the electric field is necessary for the transition rather than caused by it.
Bibliographic Reference: Article: Proceedings Vol II of 1998 International Congress on Plasma Physics 25th EPS Conference on Controlled Fusion and Plasma Physics, (1998)
Record Number: 199910913 / Last updated on: 1999-07-05
Original language: en
Available languages: en