DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 495: Can n=3 fields raise n=1 error field thresholds? | ||
| Name: | Richard Buttery
( |
Affiliation: | UKAEA |
| Research Area: | Error Fields | Presentation time: | Not requested | Co-Author(s): | Cole, Schaffer, la Haye |
| Description: | Test whether application of n=3 fields can raise plasma viscosity to the point that n=1 error field thresholds are increased, using a simple 2 shot test. | ||
| Experimental Approach/Plan: | Pick vanilla flavour standatrd DIII-D Ohmic plasma. Ramp n=1 fields. Repeat with n=3 applied also. Further repeats may be desirable to test result as we vary density. Ideally it would be best if we can wire I coils for both n=1 and n=3 independently. Otherwise do n=1 with C coils.
It may also make sense to do some repeats with low level of beams and apply rotation feedback with beam balancing, so that q=2 surface has the same rotation in cases with and without n=3 field. Nevertheless, the basic proof of principal is a 2 shot test - perhaps could be squeezed in at the start of a day, while NBI cranking up? | ||
| Background: | Error field scalings have been a longstanding theoretical problem, with robust experiment data (particularly density scalings) not matched by theoretical models. However a new model (Cole et al) appears to be able to explain the data in terms of resonant error fields being accompanied by non-resonant (NR) components. These NR fields increase plasma viscosity, thereby making the localised braking of q=2, and consequent error field penetration, harder. This modifies the density dependence of the threshold scaling.
This also raises the possibility of a new technique to reduce plasma sensitivity to error fields, by deliberate application of non resonant fields to increase the plasma viscosity. Indeed, such an effect may already play some of the role in D3D, where the correction of the C coils has historically been hard to understand in the context of in vessel intrinsic error measurements (although Park's ideal response model goes some way to explaining this also). | ||
| Resource Requirements: | Ohmic, I coils, C coils. Some NBI if 2nd part pursued. | ||
| Diagnostic Requirements: | magnetics. CER for second part. density profiles. | ||
| Analysis Requirements: | Some analysi of optimal phasing and plasma configuration for n=3 fields is needed - want large amplitude at q=2 surface. | ||
| Other Requirements: | -- | ||
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