DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 80: Core transport barriers in EC-heated discharges | ||
| Name: | Max Austin ( |
Affiliation: | University of Texas |
| Research Area: | Transport | Presentation time: | Requested | Co-Author(s): | K. Gentle
K. Burrell |
| Description: | We want to investigate unusual transport properties observed in recent DIII-D discharges with off-axis electron cyclotron heating. In experiments this past year employing ECH, steady-state hollow Te profiles with sharp changes in gradients were seen in low density, low current discharges. These profiles are reminiscent of those on the RTP tokamak which were indicative of core electron transport barriers. We propose to investigate the thermal electron transport in these shots with modulated ECH, looking at heat pulse propagation across the implied barrier region. Preliminary analysis indicates the discharges are developing negative central shear and the radii with the sharp gradient changes are possibly located near low order rational q_min surfaces. | ||
| Experimental Approach/Plan: | Establish a low density, high q discharge like 129534 and apply heating with four gyrotrons to produce hollow Te profiles. Modulate one of the four gyrotrons, or add modulated power from a 5th gyrotron at a different radius to create heat pulses for transport analysis. Add neutral beam blips to some discharges to measure q profile with MSE data. Increase the plasma current to change the target q profile. Vary ECH deposition radius either during a shot with Bt ramp or shot-to-shot with launchers and look for step-wise changes in transport. Collect ne and Te fluctuation data for radii near the apparent transport barriers. | ||
| Background: | Discharges with strong ECH exhibiting steady-state hollow Te profiles and step-wise changes in transport were first seen it the RTP tokamak. The observed electron transport behaviour was attributed to good surfaces near low order rational q values in a reverse shear profile. This ties in with recent DIII-D experiments on changes in transport seen near integer q_min traversals. With the excellent diagnostic set on DIII-D including ECE, MSE, and fluctuation diagnostics, it should be possible to attain improved understanding of the role of special values of the safety factor in electron transport. Observation of zonal flow structures and changes in turbulent fluctuations would lead to validation of the rational-q transport model. | ||
| Resource Requirements: | Three neutral beam sources, including 30L.
At least four gyrotrons, nom. 2.4 MW total power and 1 sec pulse length. | ||
| Diagnostic Requirements: | ECE radiometer, FIR scattering, Correlation ECE, BES | ||
| Analysis Requirements: | Toray, possibly GYRO. | ||
| Other Requirements: | -- | ||
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