DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 75: Simultaneous Suppression of 3/2 and 4/3 NTM with ECCD | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | Use co-ECCD at both the q=1.33 and q=1.5 surfaces to simultaneous suppress both the 4/3 and 3/2 tearing modes. Determine if an improved confinement state can be obtained, relative to plasmas with EC heating but no current drive (or NTM suppression). Determine if the beta limit is significantly affected. If sufficient gyrotron power exists, this idea can be extended to the simultaneous suppression of the 3/2 and 2/1 modes. | ||
| Experimental Approach/Plan: | (1) Divide the gyrotrons into two groups. The smaller group is aimed at the q=1.33 surface near the inner midplane. Its location is controlled by varying either R or BT. The larger group is aimed at the q=1.5 surface by poloidally steering the antennae upwards. Its location is controlled by either real-time steering or by shifting the plasma vertically. (2) Prepare target hybrid plasmas with beta_N=3 at either q95=4.4 or q95=3.1. (3) First suppress only the 3/2 NTM to determine the minimum amount of ECCD power required. Compare these cases with fiducial discharges with EC heating only. (4) With the 3/2 NTM suppressed, use remaining gyrotrons (but no more than necessary) to also suppress the 4/3 NTM that becomes dominant after the 3/2 mode is gone. Compare this with a fiducial case where the gyrotrons aimed at the q=1.33 surface are changed to radial injection. (5) Compare the plasmas with simultaneous 3/2 and 4/3 suppression to fiducial plasmas with no NTM suppression but same amount of EC heating. (6) For plasmas with both 3/2 and 4/3 suppression, determine beta limit for 2/1 NTM. | ||
| Background: | When the 3/2 NTM is suppressed by ECCD, the 4/3 NTM becomes unstable. While the 4/3 mode is likely more benevolent than the 3/2 mode (not proven for the case of ECCD suppression because of the deleterious effects of electron heating on confinement), the 4/3 mode is still expected to have some negative consequences. Therefore, it would be interesting to suppress both the 3/2 and 4/3 modes using ECCD. Since it only requires 3-4 gyrotrons to stabilize the 3/2 NTM, it is expected that the remaining gyrotrons can stabilize the 4/3 NTM which is at smaller radius. This may result in higher confinement, but to prove this fiducial discharges with the same electron heating but no current drive need to be studied. | ||
| Resource Requirements: | NBI: All 5 co sources are required.
EC: Minimum of 5 gyrotrons. | ||
| Diagnostic Requirements: | MSE is critical. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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