DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
Print this page

Print this page
Title	20: L-H transition Trigger Physics/ Main Ion Momentum Balance
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, L. Zeng, J.A. Boedo, T.L. Rhodes, E.J. Doyle	ITPA Joint Experiment :	No
Description:	This experiments attempts to simultaneously measure all terms in the radial main ion momentum balance across the LH-transition with high time/spatial resolution, including the Reynolds stress, main ion poloidal and toroidal velocity, and ion diamagnetic flow component as well as total ExB flow. Helium plasma will be used to enable main ion edge CER. The goal is to establish simultaneously and with high time/spatial resolution the turbulence fields (,E_pol~), turbulent eddy topology changes (via BES), the Reynolds stress radial gradient, and the response of poloidal/toroidal ion velocity, in order to identify/characterize the L-H transition trigger.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Low triangularity, LSN He plasmas near power threshold will be used to allow probe measurements up to ~ 1 cm inside the LCFS (reference shots #140439 and #149725). The outer gap/ upper triangularity will be modified to achieve optimum spatial CER coverage of the edge/pedestal region. The main diagnostic challenge is to optimize the CER SNR so that the expected initial poloidal/toroidal ion velocity excursion can be observed as the L-H transition sequence is triggered. Both "regular" and limit cycle transitions will be used. Extended (500 ms) limit-cycle transitions (ref. #149725 in D_2 plasma) allow phase-lock analysis of spectroscopic ion flow velocities, turbulence level, and ExB velocity (via DBS/BES) to substantially improve SNR and time resolution. This should allow us to obtain turbulence, flow, stress gradient, and nonlinear energy transfer data (from probe data) with sufficient accuracy to test against recent L-H transition models.
Background:	Recent experiments in DIII-D, EAST, and HL2-A have measured the Reynolds stress radial gradient and the rate of nonlinear energy transfer from the turbulence spectrum. These experiments were carried out in limit-cycle L-H transitions, where the transition dynamics can be investigated on an expanded time scale. However, DIII-D has the unique advantage of high spatial resolution diagnostic coverage via BES, DBS, and CER. The time evolution of the ExB velocity (and velocity shear) and, separately, the diamagnetic component of the ExB velocity (reflecting ion pressure profile evolution) have been successfully measured across the transition. However, the vXB term in the momentum balance has not been directly measured, but constitutes the essential link to establish poloidal/toroidal momentum drive during the transition.
Resource Requirements:	30, 330, and 150 Beams, He plasma
Diagnostic Requirements:	BES large array, DBS5/DBS-8, V/Q-band profile reflectometry, midplane reciprocating probe, CER tuned to He+ (4686A)
Analysis Requirements:	--
Other Requirements:	--