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Title	31: Test of Turbulence Spreading Using Turbulence Propagation
Name:	Clinton (Craig) Petty petty@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Turbulence & Transport	Presentation time:	Not requested
Co-Author(s):		ITPA Joint Experiment :	No
Description:	The question of turbulence spreading, that is, whether turbulence is or is not a strictly local phenomenon, can be precisely tested by modulating the turbulence (and plasma profile) at a fixed location and then monitoring the propagation of the turbulence (and plasma profiles) away from this region. If the turbulence propagation speed is much faster than the temperature or density propagation speed, then this can be attributed to turbulence spreading. For this purpose it does not matter much how the turbulence is modulated; it can be a simple amplitude modulation or something more sophisticated such as a modulation of the radial correlation length. The most likely source of modulation is ECH, either as a monopolar change in the electron temperature profile or as a "swing" experiment where the ECH deposition is alternated between two (closely spaced) location. The turbulence diagnostic must be capable of covering a large radial range, so the 32 channel linear array of the BES diagnostic is ideally suited for this experiment. An 8 channel DBS diagnostic would also be useful to monitor the propagation of intermediate k turbulence.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	To minimize MHD, this experiment will use an L-mode plasma with 1-2 sources of continuous NBI for diagnostic purposes (BES, CER, MSE) and 6 gyrotrons for turbulence modulation. If the beam power needs to be limited to 1 source, repeat shots can be taken to switch between beams. The ECH modulation rate should be relatively high (~100 Hz) to allow an accurate measurement of the propagation speed. Actually it is preferable to study several different modulation rates, so repeat shots will be taken to cover the range 25-200 Hz. At least two ECH deposition positions should be studied, one near the axis to observe outward propagating turbulence and one near the edge to observe inward propagating turbulence.
Background:	While the ECH "swing" experiment led by Jim DeBoo has similarities to this proposal, in that case the ECH modulation was too slow to obtain the phase delay information that is crucial to this proposal. Also the radial spread of the tubulence modulation was limited in DeBoo's case, perhaps a consequence of the "swing" arrangement. Therefore, a monopolar modulation of the ECH at relatively high frequency is preferred for this proposal.
Resource Requirements:	Beams: 30LT, 330LT, 150LT ECH: Six gyrotrons
Diagnostic Requirements:	BES 32 channel linear array DBS 8 channel array
Analysis Requirements:	GYRO simulations will be done after the experiment.
Other Requirements: