DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	30: New Optimal Plasma Shape for AT Scenario?
Name:	Clinton (Craig) Petty petty@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Steady State Heating and Current Drive	Presentation time:	Not requested
Co-Author(s):		ITPA Joint Experiment :	No
Description:	For the high q_min, steady-state AT scenario, use the "ITER Similar Shape" (e.g., lower SND shape in shot 129323) rather the plasma shape from the standard unbalanced DND shape . In the low qmin hybrid scenario, the ISS is proved to have high beta limits (ideal with-wall limit greater than beta_N=5) and low electron heat transport. If these properties are present in the q_min>2 AT scenario, the result will be (1) higher electron temperature (and higher confinement), and (2) higher noninductive current fraction.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	The main objective of this experiment is to repeat the high-beta, steady-state AT scenario with qmin>2 but with the ISS plasma shape given by shot 129323. The heating waveforms during the current ramp up phase will been to be optimized to raise q_min above 2 at the beginning of the flat top phase. If stronger cryopumping is desired to reduce the plasma density, than reverse BT direction may be required.
Background:	During an ECCD stabilization experiment in 2007, it was recognized that the discharges developed had some interesting properties (example: shot 129323). Although RWM feedback stabilization was not being used, the plasma beta exceeded the ideal no-wall limit with beta_N reaching 3.5 before the beam power topped out. Even more interesting was the fact that the core electron temperature was ~1 keV higher than normal for the hybrid scenario. This was a result of a much lower than typical electron heat transport. Usually for the hybrid scenario in the standard AT plasma shape, heat loss through the electron channel is dominant. This is attributed to ETG-scale turbulence. However, for the lower SND shaped used in this ECCD experiment, the electron heat loss was much lower than the ion heat loss. This plasma shape was used for high-beta, steady-state hybrid experiments in 2008. Here it was found that even with 3.0 MW of ECCD and Te=Ti except near the axis, the confinement time remained high with H_98=1.4. This is a much better transport result than for ECH hybrid experiments in the standard AT plasma shape where H_98 normally drops below 1.1. Stability analysis of kinetic EFITs with correct edge current density profiles using DCON found that the ideal n=1 with-wall limit was very high, more than beta_N=5.
Resource Requirements:	NBI: All co beams required. EC: All 6 gyrotrons required. BT: Reverse BT direction may be desired for improved density control in lower SND shape. I-coil: Dynamic error field correction is desired.
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