Influence of the plasma shape on mode locking during the plasma ramp-up in TCV
Locking modes have occasionally been seen during Tokamak à Configuration Variable (TCV) plasma ramp-up. Results are given of a study carried on the regions of the operational domain where the locking modes occur, together with suggestions for operation scenarios which avoid regions with significant probability of encountering locking modes. Locking modes are considered to be ultimately fatal as soon as they appear in the plasma. The regions in the operational domain to avoid are therefore those close to their birth place. The birth time can be deduced from the spectogram of a soft X-ray signal. Locking modes frequently start close to a rational value of the safety factor and are located in a small region of the operational domain. Clusters of locking modes have been identified in order to define the dangerous regions. The estimated probability of encountering a locking mode is then based on the normalized distance to these clusters. To test the viability of this estimate, the prediction error from the confusion matrix was calculated. The result is already better than 15 % errors on all TCV shots. This method could be used to increase the safe operation of large tokamaks such as the International Thermonuclear Experimental Reactor (ITER) and will be tested on TCV.
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: 199811274 / Last updated on: 1998-10-27
Original language: en
Available languages: en