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	170: Nature of Energy Released During H-L Back Transition
Name:	David Eldon eldond@fusion.gat.com	Affiliation:	General Atomics
Research Area:	L-H Transition	Presentation time:	Not requested
Co-Author(s):	Boivin, Groebner, Osborne, Snyder, Tynan, Schmitz	ITPA Joint Experiment :	No
Description:	The purpose of this experiment is to determine the nature of energy released during the back transition out of H-mode and to test control of the transition speed by changing power ramp down rate. The start of a transition from H-mode to I-phase is marked by an event characterized by a flash of D_alpha light and sometimes activity detectable by magnetic probes. This is followed by several smaller bounces of decreasing brightness (in D_alpha) which resemble limit cycle oscillations described by the predator prey model. Are these flashes the results of simple bursts of enhanced transport, or are they related to some unstable mode? How does energy loss to the divertor compare to ITER requirements? The predator prey model predicts that adjusting the rate at which input power is decreased will control the length of an I-phase during the back transition. This will be tested.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Keep one beam on throughout the I-phase for diagnostics, power with de-rated beams so that power can be removed in small increments. Different power ramp down rates will be tested with multiple L-H and H-L transitions per shot, as in 148698 and similar. One hope is for bunch mode Thomson scattering to capture the start of the back transition, or very soon before it. All possible profile diagnostics are desired for stability analysis leading up to the H-L transition. One power ramp rate will be chosen for a target density scan.
Background:	--
Resource Requirements:	30, 330, 150 beams, ECH
Diagnostic Requirements:	BES array centered on pedestal, DBS, Thomson scattering in bunch mode, CER, profile reflectometry
Analysis Requirements:	--
Other Requirements:	--