DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 385: Sustained rotation of 2/1 for locking prevention, rotational mitigation and to assist ECCD control | ||
| Name: | Francesco Volpe ( |
Affiliation: | ORAU |
| Research Area: | NTM Stabilization | Presentation time: | Requested | Co-Author(s): | R. La Haye |
| Description: | |||
| Experimental Approach/Plan: | Similar to #384, except that the applied field rotates, initially at 1Hz, and then is accelerated. Sustained rotation (a.k.a. entrainment) at up to 180Hz in the absence of ECCD has been already demonstrated. As a next step, on one hand we want to add ECCD (which will introduce a layer of complication, e.g. with respect to the alignment and maintaining it) and on the other we want even faster rotation. The concomitant linear increase of I-coil current during constant acceleration proved helpful. As a refinement, a non-linear current ramp taking into account partial cancellation by image current in the walls will be utilized.
We will also try to reproduce and understand the unexpected mode mitigation obtained during the frequency ramp at about 10Hz, which might be related to the natural frequency of the quasi-stationary mode (QSM). However, not that that was a mitigation. ECCD will be necessary for full stabilization, with the advantage that, once it is forced to rotate, the locked mode can be treated as a rotating NTM, and the same control strategies can be deployed against it. Furthermore, because the frequency and phase of rotation will be known and controllable, the control by modulated ECCD is expected to be easier. Like #384, compare pre- and post-locking intervention. The former is expected to be more efficient, as it would "catch the mode" and sustain its rotation without letting it lock at all. | ||
| Background: | In June 2007, a mode previously locked to the wall was locked to a rotating n=1 field generated by a travelling wave in the I-coils. The mode was unlocked and accelerated at up to 180Hz, thanks to a concomitant I-coil current ramp, to compensate for shielding from image currents in the wall. During acceleration, mitigation was observed at about 10Hz.
This proposal is strictly related to #88 by G.Jackson and F.Volpe. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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