DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 308: Resonant vs non-resonant braking | ||
| Name: | Andrea M. Garofalo ( |
Affiliation: | Columbia University |
| Research Area: | Rotation Physics | Presentation time: | Requested | Co-Author(s): | Degrassie, Cole, Hegna, Callen |
| Description: | A systematic study of the braking physics that includes data in plasmas with co-Ip NBI, ctr-Ip NBI, and no NBI (ECH only) is necessary to further our understanding of the interaction between a rotating plasma and error fields, both resonant and non-resonant. This is important in order to assess the thresholds of tolerable error fields for ITER (ITPA Joint Experiment MDC-12). This proposal includes braking scans in normal Ip, reverse Ip, D plasmas and He plasmas. | ||
| Experimental Approach/Plan: | This is the continuation and extension of experiments started in FY07 (MPs 2007-04-02 and 2007-04-04). We will use the C-coil for optimal correction of the n=1 error field, determined via DEFC. We will use the I-coil to apply braking. The braking is applied after all profiles have reached nearly stationary conditions. We plan to increase the braking slowly, through a succession of torque equilibrium states, and remove the braking field quickly, to also observe the response to a step. Crucial requirements are to maintain the plasma density, beta and the injected NBI torque constant during the application of the braking, which requires careful setting of the PCS feedback control of the NBI and of the density.
We will carry out shot-to-shot scans of the NBI torque, of beta, of the density, and of q95. The scan of the NBI torque is aimed at investigating the existence of an offset rotation in NTV physics for n=3 braking, and the threshold for rotation bifurcation in the induction motor model for n=1 braking. For a clear understanding of the results in very low torque cases, a day of experiments in Helium plasma is essential. The scan of beta is aimed at investigating the effect of the plasma response during n=1 braking, and the NTV dependence on Ti and dTi/dr for n=3 braking. The scan of the density is aimed at investigating the NTV dependence on collisionality. The scan of q95 is aimed at investigating the effect of the plasma response during n=3 braking. In addition to study braking by n=1 fields and by n=3 fields separately, we propose to study the combined effect of n=1 and n=3 braking, since a recent paper by Cole, Hegna, and Callen predicts an ameliorating effect of the n=3 field on the thresholds for bifurcation. | ||
| Background: | MPs 2007-04-02 and 2007-04-04 have begun on the effort to generate systematic scans of various parameters. Several discharges from these experiments could be use as starting points for the new experiments. In particular, these experiments have shown:
- that rotation bifurcation requires smaller vacuum field at higher beta, but with sufficiently large applied field it occurs at low beta as well - that an island forms during the bifurcation of rotation with n=1 braking - that the bifurcation occurs at rotation=half of the unperturbed rotation, at least for unperturbed rotation large enough that the C vs. D difference can be neglected - that the NTV offset rotation is in the counter-Ip direction, and of the order of the ion diamgnetic rotation - that a significant n=3 error field is present in DIII-D discharges, presumably due to the B-coil bus feed - that odd parity vs. even parity of the n=3 field leads to the same braking, at least for the discharges considered | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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