DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 20: RMP penetration vs rotation | ||
| Name: | John Degrassie ( |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Not requested | Co-Author(s): | T.Evans |
| Description: | *The key hypothesis is that at high q95 the plasma will be resilient against RMP-induced locking at low toroidal velocity. We will run the I-coils in n=3 odd parity for which the ELM-suppression resonance occurs just above q95 = 7. Using admixtures of counter beam we will vary the toroidal velocity and measure the threshold for RMP ELM-suppression. We anticipate that the threshold I-coil current will depend upon rotation rate, due to the physics of error field screening, and perhaps other reasons. A plot of these data will be the primary product of this experiment, leading to a flurry of potential theoretical explanations. | ||
| Experimental Approach/Plan: | *Re-establish RMP ELM-suppression with n=3, odd parity at q95 ~ 7. Vary the toroidal rotation velocity with varying amounts of counter-beam substitution and measure the threshold I-coil current for ELM-stabilization at each velocity level. The typical reduction in toroidal velocity with I-coil turn-on must be accommodated as we see what happens in the experiment. It may be advantageous to use NBI torque feedback on a velocity channel, at fixed power, to select a velocity point. We need to obtain at least three distinctly different target velocities (at the suppression threshold) and measure the necessary I-coil current at each. | ||
| Background: | *Attempts to study the effect of toroidal rotation on RMP ELM-suppression with the standard q95 ~ 3.5, n=3 even parity scenario have been plagued by RMP-induced locking as the toroidal velocity is reduced. This is important to study because of the need to experimentally understand the effect of toroidal rotation on error field penetration, and the accompanying so-called plasma response.
*There has been demonstrated an RMP ELM-suppression resonance at q95 ~ 7 using n=3, odd parity. The plasma should be far more tolerant of RMPs at low rotation at this q95, allowing the possibility of getting data on penetration vs velocity. We will measure the I-coil current threshold as an indicator of field penetration, i.e. screening. | ||
| Resource Requirements: | NBI: 7 sources. | ||
| Diagnostic Requirements: | Standard for RMP experiments. | ||
| Analysis Requirements: | Standard for RMP experiments. | ||
| Other Requirements: | -- | ||
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