DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
Login | Review | Submit | Logout | Help
Questions about this website? Contact Andrew LeBlanc Questions about ROF? Contact Chuck Greenfield
| Title | 162: Can we prevent locked mode from being locked ? | ||
| Name: | Yongkyoon In ( |
Affiliation: | FARTECH, Inc. |
| Research Area: | Rotation Physics | Presentation time: | Requested | Co-Author(s): | Jin Soo Kim, Michio Okabayashi, Holger Reimerdes |
| Description: | The proposal is to assess if a mode-locking is avoidable by taking a control action in pre-locked stage. | ||
| Experimental Approach/Plan: | In high beta, low torque plasmas, locked modes were frequently observed. However, to assess if locked modes are avoidable in pre-locked stage, low density plasmas below the ideal MHD no-wall stability limit would be primarily used, unless other plasma conditions (e.g. high beta, low torque plasmas) are identified to be more favorable to locked modes.
To avoid locked modes from being locked, the following attempts will be made in pre-locked stage using; 1) FAR-TECH's model-based dynamic Kalman filtered algorithm 2) Complex gains to provide toroidally advanced phase 3) Rotating field that would interact with a pre-locked mode. Assuming that the attempts in Step 1) show positive progress in terms of plasma responses, we may need to do some gain scans to optimize the effectiveness of the applied field. If no satisfactory responses are obtained in Step 1), we will attempt other approaches to see if the locked mode can be diverted using complex gains or rotating fields. | ||
| Background: | During high beta, low torque experiments, locked modes frequently occurred, even after reasonably good error field correction was provided. Interestingly, the RWMID algorithm, which combines the matched and Kalman filters based on FAR-TECH's DIII-D/RWM model, showed that the growth of locked mode has remarkable similarity to that of typical n=1 RWM in pre-locked stage. Considering that locked modes cannot be easily unlocked and no control is taken to avoid them, we might be able to take advantage of the model-based RWM algorithm to suppress or divert the locked modes electromagnetically.
Regarding complex gains, recent RWM experiments showed that the coil current demands were significantly reduced at a toroidally shifted angle from the measured mode phase which is typically attributed to 'unknown' error field. Thus, using complex gains might tackle the 'unknown' error field that might be linked to locked modes more directly. As for rotating fields, the pre-locked mode, which is not locked yet, would interact with the applied rotating field where the electromagnetically moving field would divert the locked stage. Compared with MHD spectroscopy, this approach of rotating field will be almost the same except the necessity that the applied magnetic field perturbations should affect the plasma motion. | ||
| Resource Requirements: | 4 co-beams and 2-counter beams, 4 gyrotrons for ECCD | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | FAR-TECH's model-based RWMID algorithm | ||
Print this page