DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 198: Tearing Mode locking avoidance with toroidal phase advance in the feedback | ||
| Name: | Michio Okabayashi ( |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Disruptions | Presentation time: | Requested | Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait |
| Description: | The feedback experiment in last year has shown very interesting results on the tearing mode behavior. The feedback operated with toroidal phase shift can synchronize the I-coil currents to the tearing mode, and not only prevent the mode from locking, but also modify the mode characteristics. The scheme can be applied for successful maneuverability of tearing mode in ITER once RWM control coil is installed.
Observations were: (1) The Feedback can shift freely the tearing mode direction and frequency without losing the stored energy. The feedback fields accelerate/decelerate the mode and, interestingly, the mode frequency is lower by two-three times in the CTR direction (to the plasma rotation) compared to that in the CO direction. (2) The synchronization transition from 0.5-1 kHz frequency to the feedback-controlled frequency (20-60 Hz) is smooth when the phasing is correctly adjusted. The choice of +30 degrees (CTR-direction of the mode) is very favorable, but so far only one shot tried. On the other hand, the -30 degrees (CO- direction of the mode) causes mode locking and beta collapse, which was reproducibly observed more than several shots. The zero phase shift may be acceptable. These results suggest that the tearing mode is quite maneuverable so that the mode can be slowed down to low frequency range, and then can be controlled. Although it is to be examined further whether the tearing mode can be quenched in time, it seems, at least, we can sustain as a forced rotation-tearing mode. However, caution is to be made that this can occur only when the error field correction is extremely well compensated and of course only with high bandwidth amplifier-coil system. We conclude that it is worthwhile to pursue this subject further, considering the possibility of the ITER application with internal coils | ||
| Experimental Approach/Plan: | Proposed experiments
(1) To survey systematically the impact of feedback toroidal phase on tearing modes (2) To explore possibilities of quenching by varying the phase/gain in time (3) To explore the implication to ITER internal coil option. | ||
| Background: | -- | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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