DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 374: Assess optimal Error Field Correction by modulating I-coils at incommensurable frequencies | ||
| Name: | Francesco Volpe ( |
Affiliation: | ORAU |
| Research Area: | Error Fields | Presentation time: | Requested | Co-Author(s): | -- |
| Description: | Perform several non-destructive Error Field Correction (EFC) tests within a single discharge, including non-resonant components | ||
| Experimental Approach/Plan: | Feed AC currents of incommensurable frequencies to each pair of I-coils in order to generate error fields that are different at every instant. Infer from plasma rotation or other indicator what set of currents gives best error correction. | ||
| Background: | Most of the times, optimal EFCs are assessed by "trial-and-error", with a new EFC being tested in each shot. One of the reasons for this is that the current indicator of optimal EFC is the lowest density at which the plasma can be ramped down without locking. This usually results in a disruption and can thus be considered a "destructive test" (destructive of the plasma). Utilizing a non-destructive indicator such as the plasma rotation (faster or slower, depending on how strong the magnetic braking from the residual error field is) would allow multiple EFC tests within a single discharge. The limit on how many EFC configurations can be tested is set by the plasma rotation response time. At this point, there are various choices on how to conduct the EFC scan during the discharge. For example, one can fix the phases between the I-coil circuits and scan the currents, while keeping their ratios fixed. This would fix the 3D geometry of the EFC field and scan the overall strength of the correction. Alternatively, one can fix the strength and vary the phases so as to "rigidly" rotate the EFC. In reality, to maximize the number of configurations, one can change the amplitude and the phases, as well as the topology, including non-resonant components. The latter can be achieved by individually modulating the I-coils, which is technically possible. In particular, modulating them at different frequencies would permit to test various strengths, topology and directions of the resulting EFC. To maximise the number of configurations, distinct coils should be modulated at incommensurable frequencies (incommensurable over the duration of a discharge, or a number of discharges). | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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