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Title	134: Pedestal stability and divertor transport studies with feedback-controlled snowflake configuration.
Name:	Vsevolod Soukhanovskii vlad@llnl.gov	Affiliation:	Lawrence Livermore National Laboratory
Research Area:	Divertor & SOL Physics	Presentation time:	Requested
Co-Author(s):	Plasma Control Group (Kolemen? Ferron? Hyatt?), S. L. Allen, T. Petrie, D. D. Ryutov	ITPA Joint Experiment :	No
Description:	Initial snowflake divertor configuration studies have been highly successful, however, they clearly demonstrated the need for magnetic feedback control. We propose to implement the X-point tracking algorithm in PCS, and experiment with control actuators and limits. The ultimate goal is to be able to control distance between null points and their relative orientation. This would enable utilization of snowflake divertor configuration as laboratory for pedestal and SOL transport studies. Precise feedback control would enable studies of ideal and snowlfake-plus configurations which are now hardly possible. Physics studies will include 1) Pedestal profiles and magnetic shear will be measured as functions of sigma (distance between null points). 2) Divertor heat flux, T_e and radiation profiles will be measured as functions of sigma (and effectively, as functions of connection length, flux expansion, and additional strike points). Feedback control would also enable snowflake configurations of medium and lower triangularities, effectively placing the snowflake divertor over the region diagnosed with divertor Thomson scattering system, as well as combining ITER shape with snowflake configurations. Feedback control would also enable studies of snowflake divertor compatibility with cryopumping, important for NSTX-U program and ST-FNSF concept development.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	1) Need to elevate priority of the snowflake feedback control with the Plasma Control Group. 2) Implement and test null point tracking algorithm for snowflake configuration identifications in PCS 3) Model and develop control scenarios, e.g., control hight and radius of X-points, X-pt vs OSP, etc 4) Execute experiment to test scenarios and demonstrate controllability of sigma and nulls orientation 5) Execute physics study to measure pedestal and divertor profiles as functions of sigma for snowflake-minus configuration 6) Execute experiment to compare with snowflake-plus and ideal snowflake (which may have more impact on pedestal stability)
Background:	--
Resource Requirements:	Need to elevate priority of the snowflake feedback control with the Plasma Control Group.
Diagnostic Requirements:	--
Analysis Requirements:	--
Other Requirements:	--