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Title	15: Edge rotation shear threshold for QH-mode access
Name:	Keith Burrell Burrell@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Inductive Scenarios	Presentation time:	Not requested
Co-Author(s):	A.M. Garofalo	ITPA Joint Experiment :	No
Description:	QH-mode requires sufficient shear in Er/RBtheta. A key question is what is the proper frequency to compare this to in order to produce a nondimensional quantity. Basic MHD theory suggests the Alfven frequency is the correct one for comparison. This experiment seeks to test that.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	This experiment will be done in reverse Ip QH-mode plasmas with shape similar to that in shot 141439. The threshold in Er/RB_theta for the QH-mode will be found at each condition by varying the rotation and, hence, Er by changing the input neutral beam torque. The density and toroidal field will be varied and the threshold found at various conditions. Edge sweeps will be used in order to improve the spatial resolution of the Er measurement. Data in QH-mode and ELMing H-mode will be obtained. Data both with and without NRMF fields will also be obtained.
Background:	Shear in the edge toroidal rotation frequency associated with the E x B drift Er/RB_theta has been shown to exceed a threshold when the plasma is in QH-mode. This shear correlates much better with the existence of QH-mode than the shear in the edge carbon rotation speed. In plotting the shear in Er/RB_theta, previous work chose to normalize to the Alfven frequency, since that frequency plays a key role in many MHD modes. Using this normalization, data from shots with different Alfven frequencies all showed the same threshold. However, we do not know if the Alfven frequency normalization is really correct. This experiment is designed to check that normalization by studying the threshold as a function of density and toroidal field, which are the physics variable that enter into the Alfven frequency.
Resource Requirements:	Reverse Ip. 6-8 neutral beam sources.
Diagnostic Requirements:	All profile diagnostics, especially edge CER. Fluctuation diagnostics optimized for edge views of the EHO, especially BES and ECE-I.
Analysis Requirements:
Other Requirements: