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	328: Error field correction at low rotation
Name:	Wayne Solomon solomon@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Stability & Disruption Avoidance	Presentation time:	Not requested
Co-Author(s):	AM. Garofalo	ITPA Joint Experiment :	No
Description:	The aim of this experiment is to determine if there is a preferable error field correction to use at high betaN and low rotation.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	We should begin by utilizing the dynamic error field correction (DEFC) system to search for an improved correction, similar to what was attempted previously in the low torque AI experiments. Different to that attempt, we should perform the beta ramps needed for DEFC in a low torque/rotation discharges, stabilized against 2/1 NTMs with ECH. In addition, some effort should be made to perform a specific correction arising from the B-coil current feed. This might best be done using independent feedback on the upper and lower I-coils using the new magnetics. We should then remove the ECH stabilization and compare the accessibility to these low torque states between the different EFCs. If an improved EFC is obtained that allows stable, high betaN, low torque operation, then the torque should be ramped up to large co-NBI. Measurements last year indicated that it was difficult to spin the plasma up from the low torque state, perhaps indicative of an edge island - improved EFC may help avoid opening this island and remove the apparent hysteresis in rotation and confinement.
Background:	Experiments in FY11 attempted used DEFC to determine an improved EFC, based on a beta ramp at high rotation. The DEFC approached a solution that used approximately 50% higher coil currents than the standard EFC algorithm, a result that has often been noted for high beta plasmas. However, when these new multipliers were applied for use during torque ramp downs at fixed betaN, we did not realize any benefit in terms of the lowest achievable torque before 2/1 onset. The question remains whether the plasma becomes more sensitive to different error fields at low torque (for example, increased sensitivity to the localized B-coil error), which a different EFC optimized at low rotation may better deal with.
Resource Requirements:	1 day expt, 6 gyrotrons, 210 beams, DEFC capability (independent upper/lower I-coils, and C-coils)
Diagnostic Requirements:	--
Analysis Requirements:	--
Other Requirements:	--