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	270: L-mode Turbulence and L-H Transition Characterization in Snowflake Divertor Plasmas
Name:	Maxim Umansky none	Affiliation:	ZZZ
Research Area:	Divertor & SOL Physics	Presentation time:	Requested
Co-Author(s):	B. I. Cohen, D. Ryutov, V. Soukhanovskii, S. L. Allen, J. Boedo, R. Groebner, M. Makowski, G. McKee, T. Petrie	ITPA Joint Experiment :	No
Description:	The goal of this experiment is to assess the influence of the Snowflake divertor configuration on characteristics of L-mode turbulence in the edge/SOL region and L-H transition. The experiments proposed would address the influence of the Snowflake divertor configuration on edge/SOL turbulence and compare to BOUT simulations extended to the Snowflake configuration. This builds on a successful campaign that used data from a well-characterized series of DIII-D L-mode plasmas in standard divertor configuration to validate BOUT nonlinear simulations.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Use standard L-mode shot with 1-1.5 MW ECH heating and do the snowflake transition and fast probe measurements and NBI blips for beam-assisted diagnostics (CER, BES). Measure turbulent fluctuations in the edge/SOL both in the outboard mid-plane and in the region of the X point(s) at the bottom of the device with scanning Langmuir probe and BES. Then raise the power further to transition to H-mode and monitor the power threshold and other characteristics of the L-H transition.
Background:	Recent experimental work on the Snowflake divertor configuration at DIII-D, TCV, and NSTX have demonstrated the beneficial effects of the Snowflake on reducing the heat flux density on the divertor plates by a higher flux expansion and flux splitting between a larger number of strike points. DIII-D snowflake experiments so far were done by first establishing an H-mode, and then transitioning to snowflake, so there is no L-mode snowflake data available so far. Recent BOUT fluid simulations and validation on DIII-D edge/SOL measurements (Cohen et al, APS DPP 2012, submitted to Phys. Plasmas) have been successful in characterizing and understanding L-mode edge/SOL turbulence and anomalous transport, but the influence of the Snowflake divertor on edge/SOL turbulence remains to be measured and simulated. The L-H transition power was found to be insensitive to Snowflake in TCV although ELM characteristics were affected (Piras et al, PRL 105, 155003 (2010)). The physics perhaps is that ELMs have low toroidal mode numbers and they can feel the null-point region while L-mode edge fluctuations have higher mode numbers and cannot extend poloidally to the null-point.
Resource Requirements:	Standard L-mode plasma with standard and Snowflake divertor configurations, SOL and divertor measurements, all fast edge, SOL and divertor diagnostics. This could be done in a half-day experiment.
Diagnostic Requirements:	Fast probe measurements and NBI blips for beam-assisted diagnostics (CER, BES). Measure turbulent fluctuations in the edge/SOL both in the outboard mid-plane and in the region of the X point(s) at the bottom of the device with scanning Langmuir probe and BES.
Analysis Requirements:	EFIT to reconstruct plasma profiles. BOUT simulations (LLNL) to compare to experiment.
Other Requirements: