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	44: Can Nitrogen impurity Seeding Improve Radiating Divertor Performance?
Name:	Thomas Petrie petrie@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Divertor & SOL Physics	Presentation time:	Not requested
Co-Author(s):	--	ITPA Joint Experiment :	No
Description:	A direct comparison of an argon-seeded radiating divertor with a nitrogen-seeded radiating divertor is the focus of this experiment. Two major tokamak research facilities (Asdex-U and C-mod) have reported that nitrogen has several advantages over other seeding impurities, such as argon. We propose to examine this hypothesis on DIII-D.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Our base case H-mode plasma is a lower single-null divertor with the ion gradB drift direction toward the X-point. Bt = -1.8 T, Ip=1.43 MA, q95 = 3.5, and Pinj=6-7 MW. The model plasma is shot 138548. These parameters are selected in order to facilitate direct comparisons with previous experiments, such the RMP argon-based radiating divertor. Deuterium gas is injected from he top of the vessel (UOB), while argon and nitrogen are injected into the private flux region of the lower divertor. First, nitrogen is injected into the private flux region at a non-perturbing level and three levels of a steady deuterium puff are used on successive shots: 0, 40, and 80 torr l/s. At the highest deuterium injection rate, take two additional shots at perturbing levels of nitrogen. This process is repeated for the argon injection case, so that, in total, there are ten shots. Impurity accumulation in the core plasma, distribution of radiated power, energy confinement time, and heat flux reduction as a function of pedestal density and collisionality.
Background:	Both Asdex-U and C-Mod have reported significant improvement in energy confinement by seeding nitrogen in their H-mode plasmas. Low Zeff plasmas were typical of these plasmas. In addition, nitrogen also led to a sharp drop in divertor heat flux. DIII-D has focused on argon seeding, and while obtaining good results in terms of maintaining energy confinement time reasonably well and reducing divertor heat flux, the results from Asdex-U and C-Mod suggest that DIII-D could improve performance with nitrogen. In fact, A. Kallenbach has suggested that DIII-D at least examine this possibility. This experiment does just that but with only a relatively small investment in experimental time.
Resource Requirements:	Machine time 0.5 day (in forward Bt), minimum 5 co-beams.
Diagnostic Requirements:	Asdex gauges, core Thomson scattering, lower divertor fixed Langmuir probes, bolometer, and CER.
Analysis Requirements:	SOLPS/UEDGE and ONETWO
Other Requirements:	--