DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 59: ECCD at High Electron Temperature | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive | Presentation time: | Not requested | Co-Author(s): | R. Prater, M. E. Austin |
| Description: | Measure the linear and quasi-linear ECCD efficiencies at high electron temperatures (>10 keV) for central deposition to test the CQL3D model in this extreme limit. | ||
| Experimental Approach/Plan: | The flexible ECH steering system on DIII-D allows us to study ECCD at different power densities while keeping the electron temperature approximately constant. The "linear" regime will be studied using one co gyrotron and four radial gyrotrons, while the "quasi-linear" regime will be studied using five co gyrotrons.(1) Make low density target discharges that have the potential for high central electron temperatures for at least 0.5 s. Most likely L-mode edge. Sawteeth should be avoided by either raising q(0)>1 using early NBI or increasing the error field to cause a non-disruptive locked mode. (2) Inject 5 gyrotrons radially and 1 in current drive phasing with B tuned for central deposition. Scan the parallel index of refraction for the current drive gyrotron from counter to co. Modulate the ECCD power at 5-10 Hz for a few cases if the high electron temperature can be maintained for at least 1 s. (3) Obtain fiducial discharge with all gyrotron in radial launch. (4) Set all gyrotrons to current drive phasing. Repeat scan of parallel index of refraction from couner to co. (5) If time permits, raise density to lower electron temperature and repeat some of the injection angle scans. | ||
| Background: | Previous ECCD experiments on DIII-D have focussed on measuring the effect of electron trapping. Analysis of the resulting database showed that parallel electric field effects were significant, but quasi-linear effects were not as clear. Meanwhile. experiments on JT-60U have measured the ECCD for central electron temperatures as high as 23 keV. Modeling these discharges using CQL3D showed that the parallel electric field effects were significant and the quasi-linear effect was smaller, similar to DIII-D. This was somewhat surprising since the RF power density was much larger on JT-60U than on DIII-D. Furthermore, CQL3D predicted a factor of 2 larger ECCD than TORAY-GA even for the linear regime, which is much different for typical DIII-D discharges. To help resolve some of these mysteries, it would be good for DIII-D to also study the ECCD efficiency in plasmas with high electron temperatures. | ||
| Resource Requirements: | NBI: co and counter MSE beams.
EC: Minimum 5 gyrotrons. | ||
| Diagnostic Requirements: | MSE is critical. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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