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Title	349: Density/current Scaling of Intrinsic Rotation and ITG/TEM Transition
Name:	Lothar Schmitz schmitzl@fusion.gat.com	Affiliation:	University of California, Los Angeles
Research Area:	Turbulence & Transport	Presentation time:	Not requested
Co-Author(s):	W. Solomon, T.L. Rhodes, L. Zeng, J. deGrassie, K.H. Burrell, B. Grierson	ITPA Joint Experiment :	No
Description:	Toroidal rotation reversal and a transition from LOC to SOC confinement have been observed in C-Mod [1] and ascribed to a transition from a TEM-dominated to an ITG-dominated regime and concomitant reversal of the (fluctuation-driven) residual stress. The goal of this experiment is to elucidate the current/density scaling of the residual stress via detailed measurement of the turbulence characteristics (in particular the poloidal wavenumber spectrum and radial correlation length) at the ITG-TEM transition, using purely ECH-heated L-mode and diverted H-mode plasmas.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Transitions from a mixed mode to a TEM dominated regime have been observed in ECH L-mode plasmas during previous experiments where the electron transport stiffness was investigated. The L-mode part of the proposed experiment would be based on a similar reference discharge possibly using IWL plasma to avoid an early H-mode transition. Depending on the ECH deposition location the electron temperature gradient can be sufficiently modified to access the TEM regime. A current/density scan will be performed to obtain Fluctuation/profile data across the ITG/TEM boundary will be obtained during a current/density scan in order to extract information on rotation reversal and residual stress. Transitioning to diverted shape, an H-mode transition later during the same series of shots will be used to check the dependence of rotation and fluctuation characteristics on the edge electron temperature and density gradient. DBS can measure the radial profile of (wavenumber-resolved) low-k and intermediate k density fluctuations, and CECE can measure the radial profile of electron temperature fluctuations. In addition PCI will be used to obtain chord-averaged fluctuation spectra. The main ion toroidal velocity will be estimated from high spatial resolution measurements of the ExB velocity obtained via DBS. This requires knowledge of the main ion pressure gradient (obtained via profile reflectometry, using the CER-measured carbon ion temperature (beam blips). This method has been successfully employed previously in low-Z_eff plasmas. A caveat of this method is that main ion poloidal rotation would have to be either neglected or estimated from theoretical models.
Background:	Intriguing work on the current/density scaling of intrinsic rotation, and rotation reversals ascribed to ITG-TEM transitions has been performed in C-mod [1,2]. iIn DIII-D, clear transitions from ITG/mixed mode dominated to TEM-dominated regimes have been observed in L-mode and QH-mode plasmas recently with ECH, but the concomitant changes in momentum transport and intrinsic rotation drive have not been systematically investigated. With the present high resolution diagnostic capabilities DIII-D is in a unique position to address changes in the fluctuation dynamics and outer core/edge density, temperature and rotation profiles during ITG/TEM transitions. The H-mode part of the experiment would be best performed during the initial ELM-free phase to maximize diagnostic resolution, although low-frequency ELMs may be acceptable. [1] J. Rice et al., PRL May 2011. [2] J. Rice at al., PRL Dec. 2011. This proposal has also been submitted to the ":Rotation" category
Resource Requirements:	All beams, 6 gyrotrons
Diagnostic Requirements:	DBS 5, DBS8, CECE, PCI
Analysis Requirements:	--
Other Requirements:	--