DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 72: Measuring the Structure of Tearing Modes | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Stability | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | Measure the localized structure of slowly rotating tearing modes to determine the helical perturbations in density, temperature, and magnetic field. Compare these with theoretical predictions from codes such as NIMROD. This should be done for 2/1 tearing modes and possibly for 3/2 tearing modes as well. The key is to reduce the tearing mode rotation frequency to less than ~500 Hz using a mix of co and counter NBI. | ||
| Experimental Approach/Plan: | Use plasmas in the hybrid regime to produce long lasting discharges with a large saturated 2/1 tearing mode (and 3/2 tearing mode as well). Trade off counter-injection beams for co-injection beams to bring the 2/1 mode rotation frequency to ~500 Hz. Use feedback control of the 2/1 mode frequency if the PCS has been upgraded to that feature. Use continuous 30LT and 330 beams to collect MSE and CER data at high time resolution. May need repeat shots to collect all of the CER data, and also may need repeat shots for the BES data. | ||
| Background: | Previously the co-injection of beams into DIII-D resulted in a rotation frequency of ~10 kHz for the 2/1 tearing mode. At this high frequency, only localized data from ECE and BES has been found to be useful in measuring the tearing mode structure. (Attempts have been made to collect fast MSE data, but to date no quantitative information has resulted from this.) If the tearing mode rotation frequency can be reduced to ~500 Hz using a more balanced beam injection, then localized data also can be collected by the CER diagnostic (~4 kHz rate) and MSE diagnostic (2 kHz rate, perhaps this could be increased to 4 kHz). This would allow the helical perturbations in electron density, electron temperature, ion temperature, ion toroidal and poloidal velocities, and local magnetic fields to be obtained. Possibly other diagnostic could be added to this mix. This experiment should result in an excellent dataset for which to compare with theoretical predictions to improve (or verify) our understanding of tearing modes. | ||
| Resource Requirements: | NBI: All 7 sources needed (not simultaneously). | ||
| Diagnostic Requirements: | MSE, BES, CER, ECE. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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