DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 199: RWM: Mode non-rigidity in low/high rotation plasmas | ||
| Name: | Michio Okabayashi ( |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics | Presentation time: | Requested | Co-Author(s): | M. Chance, M. Chu, A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | The Resistive Wall Mode (RWM) is usually modeled as a rigid mode in many feedback analyses. Various useful conclusions have been developed with this simple model. Here, a possible limitation due to the multi-branch coupling has been studied by using the NMA code. According to the recent NMA calculation, toroidal phase-mismatch between the mode and feedback field can induce the response of the stable branch to the feedback field. This response can be unfavorable and lead the RWM into the unstable region, since these stable branches are located in shallow stable region. The comparison between the observation and theory should provide some aspect of mode non-rigidity, which has not been clearly identified yet.
NMA code also provides a different view on the coupling between the RWM and feedback field compared to the rigid mode assumption. For example, in the ITER RWM feedback control, the coils located away from the mid-plane "off-midplane port coils" have been considered very ineffective according to the rigid mode assumption. However, the NMA code predicts these coils remain effective when the operation is combined with mid-plane coils. It is urgently needed to verify the appropriateness of the NMA code, since the decision of the ITER off-midplane port coils will be determined soon. This experiment will contribute greatly to this objective. | ||
| Experimental Approach/Plan: | Approach
Coil arrangement: (a) The non-rigid poloidal field pattern can be made in a self-regulated manner, by energizing upper / lower coil independently with two independent sets of upper/lower sensors. (b) More flexible pattern is with "autonomous feedback" where a pair of coils (facing each other toroidally connected in anti-series) is to be energized each up to 0.5 kA. Observation (1) RFA produced with extra n=1 pulses RFA will be produced by pulsed field added through I-coil and/or C-coil (2) We apply the feedback onto the RFA or its decay period, while observing the transient process. We should observe the asymmetric characteristics relative to the phase shift. The toroidal phase shift will be added through PCS system (3) Documentation The comparison of amplitude and toroidal phase between upper/lower MPID signal and at midplane, since they are least sensitive to the applied field | ||
| Background: | |||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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