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	66: 13C-methane injection into USN re C migration to walls and ITER decision about PFC target material
Name:	Peter Stangeby peter.stangeby@utoronto.ca	Affiliation:	University of Toronto
Research Area:	Plasma-material Interface	Presentation time:	Requested
Co-Author(s):	Tony Leonard, Richard Pitts (ITER), Dmitry Rudakov, Clement Wong	ITPA Joint Experiment :	Yes
Description:	Motivation: the proposed experiment will provide important information for the decision which will be made in late 2013 whether ITER should start with CFC or W at the divertor targets. One of the arguments that continues to be strongly maintained by some, e.g. at 2012 ITPA DIVSOL, against starting with C at ITER targets is that the C will migrate out of the divertor and so the C contamination of ITER will not be removed by replacing the divertor. That C will then be problematic subsequently by causing increased tritium retention. Based on our 13CH4 injection expt in DIII-D into the secondary divertor (unbalanced DN), however, such a migration pattern seems unlikely. DIII-D is the only tokamak that can inject 13CH4 simultaneously into both outer and inner primary divertors (using USN), toroidally symmetrically. Thus DIII-D can do a definitive experiment here. Inject 13CH4 into USN using both inner and outer pumping plenums, to establish if C from primary targets migrates out of divertor.	ITER IO Urgent Research Task :	Yes
Experimental Approach/Plan:	On the last day of the campaign, inject 13CH4 into USN using both inner and outer pumping plenums, to establish if C from primary targets migrates out of divertor. One day (20 shots), repeat condition, high power, ELMing H-mode discharges, with partial detachment of the outer divertor - as ITER plans to use. A comprehensive set of tiles removed for measurements of 13C surface density by Bill Wampler, Sandia.
Background:	This will be the 4th 13C-methane injection experiment done in DIII-D but the first to measure the migration out of the divertor of carbon released into the divertor plasma, simulating carbon sputtered from the targets. DIII-D's ability to inject trace gases toroidally symmetrically and using large entrance orifices, puts it in a unique position to do interpretable trace impurity expts. In other tokamaks the injection is toroidally non-symmetrical and/or involves gas injection through small orifices. Non-toroidally-symmetric injection results in non-toroidally-symmetric deposition of the 13C, which makes it difficult/impossible to find most of the 13C and makes the interpretation of the expt difficult/impossible. Typically only a few percent of the injected 13C is found in 13C-methane injection experiments in other tokamaks, while in the three DIII-D expts, ~ 50% of the 13C was found. Injection of gas through small orifices almost certainly disturbs the local plasma - although that is not possible to confirm by direct measurements since the disturbance would be quite local. Even with the far more spatially distributed gas injections used in DIII-D - where diagnosis of the plasma in the injection region is possible - we were able to measure some plasma changes to the local plasma, changes which we then incorporated in the interpretive modeling.
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