DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 86: Characterization of Turbulence Associated with TEMs | ||
| Name: | Jim C. DeBoo ( |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation | Presentation time: | Requested | Co-Author(s): | E. Doyle, T. Rhodes, A. White |
| Description: | The goal of the experiment is to create a plasma where TEMs dominate the turbulent spectrum and then turn TEMs off by reducing the electron temperature gradient scale length, a/LTe, locally. This will allow a clear correlation of measured turbulent spectra associated with TEMs and create a simplified dataset with just one dominant drift wave mode to compare with GYRO and TGLF calculations. | ||
| Experimental Approach/Plan: | As has been done previously, set up an inside wall limited L-mode discharge at low collisionality. This has been calculated to result in a TEM dominated discharge over much of the plasma. Use the ECH swing technique, where ECH power is alternately deposited at two closely spaced spatial locations in the plasma, to swing the local value of a/LTe above and below the TEM threshold. The experiment must be done at sufficiently low a/Lne in order to increase the TEM growth rate sensitivity to variations in a/LTe. Lower values of a/Lne, may be found toward the plasma center, where smaller gradients exist. Thus a scan in r/a from the plasma midradius to about r/a ~ 0.2 should be done. Other methods to reduce a/Lne should also be explored. | ||
| Background: | The ECH swing technique was used in an experiment in 2007 in an attempt to turn off TEMs in the plasma at r/a =0.5. While the technique resulted in a factor of 1.8 variation in a/LTe, no clear changes in the measured spectra in the TEM wavenumber range was observed on any of our turbulent diagnostics. Recent calculations using the TGLF code have shown that for the experimental conditions TEMs dominated the drift wave spectra at r/a = 0.5, but reducing a/LTe by a factor of 2 in the code did not change the calculated growth rate significantly, consistant with experimental observations. Additional calculations show that a much greater sensitivity of the growth rate to variations in a/LTe can be obtained at lower values of a/Lne. | ||
| Resource Requirements: | At least 4 gyrotrons and 2 MW of ECH power | ||
| Diagnostic Requirements: | Full suite of fluctuation diagnostics | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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