DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 105: Comparison of EC and NBI H-mode Thresholds | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Transport | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | Clarify the role of rotation by comparing the H-mode threshold power for co/balanced NBI and EC heating. CER data will be obtained in "pure" ECH plasma using the normal techniques developed by John deGrassie. This experiment proposes to first measure the ECH H-mode threshold (plasma conditions adjusted to place this in the range of 2-3 MW), and then fix the NBI power to the same level and conduct a torque scan to find the NBI H-mode threshold case. In addition, the H-mode power threshold for pure co NBI and balanced NBI (or even counter NBI) discharges will be documented. A comparison of the rotation profiles for all of these cases should shed light on the critical physics governing the H-mode threshold power, and allow us to make better predictions regarding the H-mode threshold power for slowly rotating plasmas on ITER. | ||
| Experimental Approach/Plan: | (1) For normal Ip and Bt direction, document the H-mode threshold power with pure ECH for LSN plasma shape. The density and bottom X-point height should be adjusted to place the ECH threshold power between 2-3 MW. (2) Keeping the plasma shape and density fixed, document the H-mode threshold powers for co NBI, balanced NBI, and counter NBI (if possible). (3) Assuming that the ECH threshold power falls in between the NBI extremes, fix the NBI power to the ECH threshold power and scan the torque to find the H-mode threshold. Document this situation. | ||
| Background: | It has been shown on DIII-D that the H-mode threshold power is lower for balanced NBI than for co NBI. However, it is not clear how this result extrapolates to slowly rotating plasmas on ITER, especially given the robust RF heating. The rotation profiles are not the same for balanced NBI and RF heating, even if the integrated torque is close to zero in both cases. This is because the balanced NBI actually induces a positive torque in the core and a negative torque in the edge, whereas the RF induced torque is negligible at all radii. One may wonder if the key to low H-mode threshold power on DIII-D with balanced NBI is the overall slow rotation rate, or some feature of the edge rotation profile where the local torque deposition from NBI is not negligible. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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