DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 180: Complete ELM suppression with n=2 RMPs | ||
| Name: | Richard Buttery
( |
Affiliation: | UKAEA |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Requested | Co-Author(s): | Max Fenstermacher, T Evans, D Howell, M Schaffer, O Schmidt, R Moyer, T Osbourne, G Jackson |
| Description: | It is proposed to extend the 4 shot proof-of-principal 2007 studies which demonstrated complete ELM suppression with n=2 fields. These shots identified a possible "sweet spot" in q95 ramps, at q95=3.4, where ELMs were completely suppressed for up to 500ms. Other narrower resonances were observed at other q95 values. The key goal of this follow up study is to confirm the location of the resonance, and test whether slower q ramps or freezing the q value, allows the ELM removal effect to be sustained longer or indefinitely. It should also explore how wide the resonance is in q95.
The initial proof of principal confirmation would take around half a day, but should be extended if a robust method is found. A range of follow up studies (vary harmonic mix with I phasing, explore several sweet spots, combine with n=3 fields could be envisaged if successful, explore collisionality dependence, and physics studies with pellets). Prioritisation committees are invited to consider also planning for an extension along these lines. | ||
| Experimental Approach/Plan: | This would pick up 2007 studies, using already optimised discharges (ITER-like shape single null), q95 ramps, and maximum possible I fields. I phasing of 120 would be used - calculated to be optimally aligned with field pitch. Error correction to be done by C coils. No RMP references will be needed of all key results. | ||
| Background: | Complete and robust suppression of ELMs is a requirement for fusion power plants and highly desirable for ITER. Present n=3 techniques have been somewhat limited in their range of applicability, although appear to demonstrate the best potential for the power plant goal. Use of other n values may establish a way of extending resonance windows, either inherent to the different harmonic (eg applying a broader resonance) alone, or by combining fields with different n.
In this proposal we are taking a first step by evaluating use of n=2 fields alone. A wide range of extensions can be envisaged, if this proved successful, and should include combining with n=3 fields if suitable wiring is possible. This experiment utilise a unique capability worldwide, in terms of DIII-D capacity to apply high amplitude n=2 fields, which through I coils flexible phasing, can have poloidal spectrum tuned for optimal resonance with the plasma. Further experiments on JET will be bid for 2008, though we should note that these will be more limited with regard to spectrum and amplitude, and the coils tend to apply higher levels of core resonance than DIII-D's I coils. Nevertheless, preliminary first tests of n=2 at JET in 2007 showed a modest ELM frequency rise, indicating a potentially viable technique. The complete suppression demonstrated in DIII-D also showed signs of strike splitting and redistribution, which may indicate edge ergodisation effects, although further studies (eg with pellets) are needed. | ||
| Resource Requirements: | I coils 240, C Coils, 4 beams, (possible use of pellets as a further diagnostic). | ||
| Diagnostic Requirements: | Usual ELM control diagnostics, with particular emphasis on pedestal measurement. Esp. CO2, TS, CER, magnetics, filterscopes, Dimes TV, IR. | ||
| Analysis Requirements: | Results should be self evident, but detailed diagnostic analysis will be required to quantify effects. | ||
| Other Requirements: | -- | ||
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