DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 225: Edge Ti (rotation) disturbance with residual stable RWM activity | ||
| Name: | Michio Okabayashi ( |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics | Presentation time: | Requested | Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | 2007 Observation
The high-N plasmas with error field correction applied show the existence of residual stable n=1 activity. Typically, the stable RWM amplitude reaches ~ 5gauss in the midplane MPID sensors. Since these weak fluctuation occurs in slow time scale ~ 100 Hz or less, we have not paid attention to these activities. However, we found that the direct RWM feedback reduced the amplitude by more than a factor of two and simultaneously reduced the edge Ti (rotation) disturbance. Here, the terminology of disturbance is used since the samping rate of Ti(rotation) was 2 ms. A hypothesis is that the n=1 activity was caused by the RFA due to the small but finite residual error field. The RFA process does capture the helical flux and then expel with the appearance of other MHD like ELMs. The dynamic error field correction (DEFC)-only is not sufficient to reduce this weak n=1 activity. This disturbance propagates into q=2 surface area. It is quite possible that these disturbances can impact the edge profile as well as the onset of other edge-related phenomena. | ||
| Experimental Approach/Plan: | Experiments
(1) Apply fast feedback above the no-wall limit in fast feedback mode in AT plasmas rather than the standard DEFC operation. (2) The better feedback can be made with using upper/lower separated sensor signals and energizing independently upper/lower I- coils. | ||
| Background: | -- | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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