DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 470: Experimental emulation of ITER port-plug RWM coil asymmetries | ||
| Name: | Michael Walker ( |
Affiliation: | General Atomics |
| Research Area: | RWM Physics | Presentation time: | Not requested | Co-Author(s): | Yuri Gribov |
| Description: | The ITER port plug coils cannot be placed so as to maintain translational symmetry in the toroidal direction. Therefore, it would be very useful to study experimentally in DIII-D the effectiveness of RWM stabilization by the C-coils when one of the coils does not take part in the stabilization. This experiment could also produce very important data for validation of codes with a multimode RWM model and 3-D model of feedback coils and conducting walls. In the same configuration, it would also be useful to attempt ELM suppression and/or error field correction on the same experimental day, to determine if such a non-symmetric configuration can be effective for these tasks. The results of this experiment can provide critical guidance for decisions regarding the effectiveness of the candidate port plug coils for the proposed multiple uses. | ||
| Experimental Approach/Plan: | Disconnect one of the opposing C-coil pairs and power only one half of that pair, leaving the other coil open-circuited to emulate the expected lack of rotational symmetry in ITER. Some re-optimization of the RWM correction matrices will very likely be required. | ||
| Background: | There is concern by the ITER team that, although the port plug coils have been shown to be effective in n=1 RWM suppression, they may negatively impact the n different from one mode spectrum. Of particular concern is the expectation that there will be some pressure to install only a limited number of the total planned set of these coils. Some understanding of this issue from actual experiments would be useful, but perhaps most useful is the provision of data that can be used to validate multi-mode models. In that case, the validated models can be used to investigate this question in more detail.
The effectiveness of these in-vessel coils for other proposed purposes is also of concern. In particular, the more urgent problem in ITER at the moment may be ELM suppression. Does such a non-symmetric configuration provide for magnetic perturbations that will suppress ELMs? Also, the present plan for the error correction coils outside the vessel is to provide only DC current. There does not seem to be a clear plan for how to optimize the current in these static coils to correct ITER error fields. More importantly, it has been seen on DIII-D that the optimal compensation is actually plasma dependent, which the present use of dynamic error field compensation addresses. The question remains, however, whether this approach (using the port plug coils) is feasible in ITER in light of the fact that the field spectrum that the port-plug coils (the only coils planned with AC capability) may not be sufficiently controllable. | ||
| Resource Requirements: | 1 experimental day | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | re-optimization of RWM control matrices. Development of proposed ELM suppression m/n spectrum. Development of approach to use this non-symmetric configuration for error field correction. | ||
| Other Requirements: | -- | ||
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