DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 383: Simultaneous control of ELMs and RWMs | ||
| Name: | Francesco Volpe ( |
Affiliation: | ORAU |
| Research Area: | Core-Edge Integration | Presentation time: | Requested | Co-Author(s): | -- |
| Description: | Simultaneously use I-coils for RMP control of ELMs and for RWM control. Look for conflicts or synergies. | ||
| Experimental Approach/Plan: | Simple superposition of AC, <1kA RWM control waveform, whatever algorithm or method it is based on, on DC, 6kA baseline for ELM control. Ramp down q95 in initial discharges, then continue at optimal values for ELM control. Try to obtain first ELM suppression above no-wall limit (and, for comparison, shots with ELM control only, RWM control only, and no control at all). | ||
| Background: | I-coils have been used with success at DIII-D to control ELMs or RWMs. It is important to assess conflicts or synergies between the two control techniques, on the way to an integrated coil system for ITER, which will have to fulfil these and other tasks, such as error field correction. The concern is that optimal current and helicity settings for RWMs might not be optimal for ELMs and viceversa.
For example, the n=1 dynamic correction for the RWMs might change the optimal q95 window for ELM control. On the other hand, from a RWM perspective, ELM-suppressing RMPs are a static, typically n=3 error field affecting the plasma rotation and thus the RWM stability. Hints of simultaneous RWM suppression and ELM mitigation can be found in A.Garofalo's shots 122591-594, where an n=3 magnetic braking field was applied with the C-coils, during n=1 RWM feed-back with the I-coils. Although the real goal of those experiments was to study RWM control in the presence of n=3 magnetic braking, they provide useful information on the interplay with RMPs for ELMs. For instance, they seem to confirm the above speculation on the modified q95 window. Although encouraging, the experiments will need to be repeated at increased n=3 current (6kA, as 3kA were marginal for ELM suppression). Moreover, the I-coils can be wired as to simultaneously apply an n=1 and n=3 perturbation. Finally it will be beneficial to drastically reduce the gas puff and move the strike point to improve the pumping and limit the collisionality, and to reduce the triangularity (was 0.6). All these modifications go in the direction of facilitating the ELM suppression. It will also be important to avoid ELM-free H-modes or temporary losses of H-mode, in order to isolate real ELM-suppression evidence. n=3 RMPs were proposed here because they are the best known and most successful RMPs. However, if successful, the same experiment could be repeated with n=1 or n=2 RMPs, which showed promising results in recent ELM control experiments by R.Buttery. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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