DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 228: Optimization of combined Dynamic Error Field Correction and Direct RWM Feedback at Low Rotation | ||
| Name: | Michio Okabayashi ( |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics | Presentation time: | Requested | Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In 2007 campaign best shots of long-duration low-rotation discharges have been frequently produced by applying DEFC through C-coil or I-coil. Near the termination in these discharges (like in 127941), the n=1 RWM mode amplitude was increased with the increase of C- or I-coil coil currents as if the system became unstable. There remains as an unanswered question whether this is due to the unstable RWM or DEFC difficulty
Proof of principle experiment of combined DEFC and RWM direct feedback has demonstrated that the combined control of the RFA by C-coil DEFC and I-coil direct feedback made it possible to reduce the ELM-driven RWM activity leading to discharge sustainment (1286312 / 128613). The optimization of combined operation of DEFC and direct feedback is one of main issues in 2008 Subjects (1) To examine whether limitation at low rotation is due to DEFC failure or unstable RWM (2) To optimize the combined operation of DEFC and RWM direct feedback process above the limitation - Including the I-coil 180 degree connection - DEFC and direct Feedback parametric scan, mainly the gain balance between the two systems | ||
| Experimental Approach/Plan: | Approach
(1) Fundamental information is taken with additional n=1 pulses - DEFC or Direct feedback will be examined in the middle of additional n=1 pulse - Transient process: the major documentation (2) The gain balance of dynamic / direct feedback (128313/312) without n=1 pulses Extra information obtained 1. Sensitivity to residual error field 2. Possible formation of magnetic island and locking 3. Uniqueness of RFA (non-rigidity?) even with same statistic error field 4. Criticality of toroidal phase shift for avoiding locking (forced rotation) Discharges Approaching in time to the operational limit in low rotation (like 127941) | ||
| Background: | -- | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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