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Title	346: Control of H-L back transition via applied RMP fields
Name:	Lothar Schmitz schmitzl@fusion.gat.com	Affiliation:	University of California, Los Angeles
Research Area:	L-H Transition	Presentation time:	Not requested
Co-Author(s):	G. McKee, Z. Yan, G. Tynan, T.L Rhodes, L. Zeng, P.H. Diamond	ITPA Joint Experiment :	No
Description:	Energy release and inductivity changes during the H-L back transition are a concern for ITER, as they can place undue stress on the poloidal field system and lead to excessive divertor heat load excursions. Control of the transition timing/temporal evolution is therefore important. This experiment will explore control of the back transition dynamics via RMP fields. Addition of RMP accomplishes two important modifications: 1) The upper pedestal density gradient can be limited/mitigated, possibly allowing trigger of the H-L back transition via NBI power ramp-down without a preceding large ELM; 2) Addition of RMPs may allow us to exceed the transition power hysteresis and allow precise control of the H-L back-transition timing.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	In H-mode plasmas in ITER-similar shape, a gradual NBI power ramp down will be performed in the presence of even parity n=3 I-coil perturbations, using (static) I-coil currents of 1-4 kA, with q95 in- and outside the ELM-suppression window.The experiment will then be repeated using odd parity. An additional experiment will be carried out with P_NBI adjusted to the power needed to maintain H-mode after the L-H transition, and adding a modulated I-coil pulse (at the fastest possible rate) to induce the back-transition. In this manner intermediate states similar to limit cycle oscillations may be accessed (LCOs have previously observed spontaneously during back transition in a low triangularity plasma)
Background:	H-L back transitions with extended limit cycles were previously observed in a low triangularity plasma. These transitions were induced via a step-down/shut-off in NBI power and typically were triggered via type-I ELMs. Control of the upper pedestal density/pressure profile via RMPs may allow us to trigger the back-transition independently of ELMs, and may also allow control of the detailed transition dynamics and energy release rate.
Resource Requirements:	All beams, pulsed/modulated I-coil (details to be determined)
Diagnostic Requirements:	BES, DBS, reciprocating probe, profile reflectometry, edge Thomson,
Analysis Requirements:	--
Other Requirements:	--