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Title	236: Wavenumber dependence of turbulence suppression in the L-H transition
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. Tynan, G.R. McKee, Z. Yan, T.L. Rhodes	ITPA Joint Experiment :	No
Description:	Recent experimental evidence suggests that turbulence reduction in the edge transport barrier varies with the perpendicular turbulence wavenumber, such that intermediate wavenumber fluctuations couple more efficiently to LF flows and are more strongly suppressed (T. Estrada, EPS 2012, L. Schmitz, Nucl. Fus. 2009). Following the temporal turbulence evolution at different wave numbers would elucidate turbulence-flow coupling and provide evidence of the energy cascade. If additionally the total energy transfer is measured (via reciprocating probe insertion), the damping rate of turbulence-driven flow can be determined. Limit-cycle transitions allow acquiring all necessary data with improved SNR and statistics.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Start with a discharge near LH-transition power threshold exhibiting extended limit cycle oscillations. Change DBS incidence angle as well as vertical plasma position to access the maximum possible range in poloidal turbulence wavenumber, and measure simultaneously turbulence level and flow evolution at each wavenumber. By scanning/optimizing shape/vertical position and DBS launch, we expect to be able to cover a wavenumber range of ~ 0.5 cm^-1 - 6 cm^-1. Data will be acquired for 4-5 wavenumber values within this range.
Background:	Limit cycle (LCO) L-H transitions have been previously investigated in detail via DBS and BES, but only limited reciprocating probe measurements have been obtained. Also, the DBS measurements have been limited to the lowest accessible turbulence wavenumber in the previous LH transition experiment (~3-4 cm^1), due to the limited number of available LCO shots. It is straightforward to assemble data across an extended wavenumber range with a sufficient number of repeat shots.
Resource Requirements:	30,330,150 beams
Diagnostic Requirements:	DBS5,8 BES, PCI, Midplane reciprocating probe
Analysis Requirements:	--
Other Requirements:	--