DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 322: Dynamic error field control for ITER | ||
| Name: | Ted Strait ( |
Affiliation: | General Atomics |
| Research Area: | Error Fields | Presentation time: | Requested | Co-Author(s): | -- |
| Description: | The goal of this experiment is to develop the use of feedback-controlled dynamic error field correction in low beta plasmas.
Such plasmas can develop non-rotating n=1 modes at low density, driven by error fields. As such a mode becomes marginally stable it should amplify the error field, just as RWMs do at high beta, providing input for the feedback system. | ||
| Experimental Approach/Plan: | Use a low-density ohmic plasma with all error correction turned off. Ramp the density down in the current flattop phase until a locked mode appears. Then turn on "slow" feedback (time constant 10-50 ms) using C-coils and SPAs. We expect to see that the feedback calls for something close to the "standard" error correction currents, and thereby avoids the locked mode.
Repeat the process in an ELMing H-mode plasma, well below the no-wall beta limit. | ||
| Background: | ITER is likely to have little or no capability to measure field errors directly. The field errors may also change as the coils and their support structures are cooled in the cryostat. Therefore "dynamic error field correction" in real time is likely to be required for all scenarios in ITER. However, this technique has so far been applied only in plasmas above the no-wall limit. The proposed experiment would provide the first demonstration of the technique in a wider range of operating conditions. | ||
| Resource Requirements: | C-coils and SPAs | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | A prerequisite is a good compensation matrix (C-matrix) in the control system to remove direct coupling of the sensors to the toroidal field, F-coils, etc. This is likely to be more critical than for dynamic error field correction at high beta. The reason is that in the high beta case, the feedback is typically turned on when the plasma current is at flattop and beta is approaching its maximum, so there is relatively little change in the coils currents. In the present low-beta case, it may be necessary to enable the feedback control early in the discharge, as the coil currents are still ramping. | ||
| Other Requirements: | -- | ||
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