DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 89: Higher Beta ELM-Suppressed Hybrids | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges | Presentation time: | Requested | Co-Author(s): | -- |
| Description: | Continue RMP ELM control experiments in the ITER shape by controlling the 3/2 NTM amplitude to allow higher normalized beta to be achieved without rotational slowing and mode locking. The 3/2 NTM amplitude can be decreased by either (1) optimizing the error field correction to obtain higher rotation rates, (2) using ECCD at the q=1.5 surface, or (3) trying higher q95 (>4) if a RMP resonant window exists. The goal is to obtain RMP ELM-suppressed hybrids with beta_N~3 (close to the ideal no-wall limit). If naturally dominant 4/3 NTM hybrids can be produced, then the ECCD suppression of the 3/2 NTM is not necessary. The higher q95 cases should work because the coupling between the 3/2 NTM and the wall is weakened as the resonant layer is moved closer to the plasma center. This ELM suppression experiment should first use only co-NBI, but once optimized results are obtained then lower rotation plasmas should be studied using balanced NBI. | ||
| Experimental Approach/Plan: | (1) Repeat previous best ELM-suppressed hybrid case 129958. (2) Optimize error field correction to obtain highest rotation rates. (3) Use ECCD at q=1.5 surface to reduce and/or eliminate the 3/2 NTM. (4) Determine new beta limit during RMP ELM suppression. (5) Add counter NBI to slow rotation rate such that M<0.1. (6) Steer gyrotrons not needed for NTM control to core deposition to obtain Te=Ti. | ||
| Background: | Experiments in August 2007 used the I-coil to completely suppress ELMs in high beta hybrids for q95=3.7. If a dominant 4/3 NTM was present, then beta_N up to at least 2.5 could be achieved during the I-coil phase (actual beta limit not known). However, if a 3/2 NTM was present, then for beta_N>2.2 the plasma rotation slowed down rapidly during the I-coil phase and a locked mode terminated the hybrid discharge. | ||
| Resource Requirements: | NBI: All 7 sources are required.
EC: Minimum of 3 gyrotrons, prefer to have 5 gyrotrons. | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | I-coil required. | ||
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