DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 372: Inducing 3/2 TM or NTM in hybrid discharges by means of modulated ECCD | ||
| Name: | Francesco Volpe ( |
Affiliation: | ORAU |
| Research Area: | Core Integration (Advanced Inductive) | Presentation time: | Requested | Co-Author(s): | R. La Haye |
| Description: | Drive current filament on the q=3/2 surface (around which island will form), by means of ECCD modulated at twice its CER rotation frequency. | ||
| Experimental Approach/Plan: | Measure with CER the toroidal rotation velocity of the 3/2 surface (identified/localized through MSE and EFIT). Repeat the shot with modulated ECCD at twice that frequency (because n=2). In case of excessive variation from-shot-to-shot or within-the-shot, some work on the PCS might allow to respond in real-time to the changes of CER frequency. Compare co- and ctr-CD, expected to drive classical and neoclassical TMs, respectively. | ||
| Background: | NTMs are not always undesired instabilities: small 3/2 NTMs are desirable in 'hybrid' discharges, where they help to prevent sawteeth. Despite the existence of consolidated experimental recipes, difficulties were recently encountered (March 2007) in developing hybrid scenarios with "natural" 3/2 NTMs. The purpose of this proposal and of #371 is to develop a tool to trigger these modes on demand, when required. The basic idea is that, in the absence of mode and therefore of filamentation, the 3/2 surface is "smooth" and consists of identical 3/2 current filaments, all carrying the same current. Artificially increasing or decreasing the current in one of them by means of co- or ctr-CD would break the axisymmetry and introduce the helical current perturbation around which an island would form. If sufficiently big (wider than 'marginal'), this island would evolve, grow and saturate. Tailoring the island to the hybrid discharge needs would then be a question of setting beta -or otherwise modifying the Rutherford equation- in such a way that the saturated width is tolerable. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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