DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 494: RWM thresholds without tearing modes | ||
| Name: | Richard Buttery
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Affiliation: | UKAEA |
| Research Area: | RWM Physics | Presentation time: | Not requested | Co-Author(s): | Rob La Haye (his idea!) |
| Description: | Use pre-emptive ECCD to prevent tearing at the q=2 surface, while exploring onset threshold (rotation, beta) for RWM. Do this at various injected torques (low to high). | ||
| Experimental Approach/Plan: | Replicate various RWM onset scenarios in the presence/absence of 2/1 pre-emptive tearing mode current drive control. Do this for balanced, low, medium and high rotation plasmas. Some time may be needed to optimise ECCD deposition, as it may be hard to discern/check q=2 location directly - use real time MSE, and try to make modes in some cases (either rotating, or if locked use 10Hz EF phase sweep to rotate it past ECE). ECCD could also be applied in reverse direction to help destabilise tearing mode (both to measure location and discern effect on RWM). | ||
| Background: | It is becoming clear that the role of error fields and generation of tearing modes are intimately related to the process of RWM onset. Indeed, recent studies at high rotation have shown an error field penetration like process. At low rotation, new D3D measurements with 10Hz forced phase sweeps of the mode (from applied error field) indicate RWM onset is accompanied by island structures from very close to the point of RWM onset.
Interstingly, the latest theoretical model (eg Liu) propose further stabilisation effects for the RWM physics from kinetic damping and precessional drifts, possibly making theoretical predictions too stable to match observations of RWM onset. This all suggests that an additional destabilising force may be playing a role in RWM experiments to date - this could be coming from the tearing mode physics, either directly from error field induced islands, or the changes to tearing stability (delta prime) that seem to come about in low torque plasmas (cite D3D baseline scenario NTM torque scan). Indeed, this even raises the possibility that the "RWM" is just a facit of an error field mode or delta prime driven mode onset. Is the real physics governing mode onset that of the tearing mode, with RWM components (although remaining stable) modifying the plasma response and energetics of the plasma to assist in tearing mode formation and generate RWM like signatures? | ||
| Resource Requirements: | Up to 6 beams including 2 counter. ECRH at least 2 gyrotrons, real time targetting from MSE. I coils for error field minimsation and phase locking control. | ||
| Diagnostic Requirements: | ECE, magnetics, MSE, CER. | ||
| Analysis Requirements: | Results should be apparent in changes in RWM thresholds. | ||
| Other Requirements: | Experience of D3D RWM experts in making target regimes. | ||
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