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Title	89: Mo, W, Al, Be DiMES net/gross erosion experiments
Name:	Peter Stangeby peter.stangeby@utoronto.ca	Affiliation:	University of Toronto
Research Area:	Plasma-material Interface	Presentation time:	Requested
Co-Author(s):	Chris Chrobak, Bill Wampler (Sandia), Tony Leonard, Dmitry Rudakov, Clement Wong,	ITPA Joint Experiment :	Yes
Description:	In theory, prompt local deposition of sputtered particles should reduce net relative to gross erosion. Definitive experimental evidence is needed. Al: proxy for Be (PhD project of Chris Chrobak). The DIVIMP code is being used by ITER to design the Be wall and needs to be bench-marked. Chris made a start in 2012. First Al layer melted, 2nd did not. With new solutions, try again. Mo: while the net/gross erosion of Mo was in good accord with expectations, transport of the Mo which did not deposit on the sample (~50%) seems to migrate further than one would expect. Evidently caused by a strong mixed-materials effect due to the substrate material that surrounded the Mo sample, namely C, which erodes very quickly cf Mo, thus rapidly "pulling the rug out from under" deposited Mo. Repeat the Mo expt but with W as the surrounding substrate material. The sputtering rate for W is significantly less than for Mo and so should make for a more interptretable expt. W: the most important high-Z. We didn't start with W because of uncertainties in the S/XB, but now we have demonstrated a non-spectroscopic method of measuring gross erosion so we can usefully do W studies with DiMES. This will provide a measurement of S/XB which will be valuable for applications generally, specifically to W expts in other tokamaks where only a spectroscopic method can be used, requiring reliable a value for photon efficiency (S/XB). For safety reasons, DIII-D cannot use significant amounts of Be and the permitted level is now 10X lower than it was the last time Be DiMES experiments were done, in the 1990s. This may preclude experiments on net/gross erosion, which require a 1 cm diameter Be layer; however, it will still be possible to perform an extremely important experiment to measure the absolute erosion (gross erosion) rate, i.e. sputtering yield for D-ion impact, Y_Be_D. This will be done using very small, 0.01 cm2 area (vs ~ 1 cm2 before) and very thin, 20 nm (vs 100 nm before) coatings, using our new discovery of a non-spectroscopic method for measuring gross erosion, namely by measuring the net erosion of a very small sample using ex situ ion beam analysis. For very small samples, gross erosion ~ net erosion. The present database for Y_Be_D has a major problem since the values from careful PISCES experiments are an order of magnitude less than measured with ion accelerators and spectroscopically in JET. This has serious consequences for ITER since it causes an uncertainty of an order of magnitude in the predictions for the lifetime of the Be wall as well as for the rate of tritium retention by Be-codeposition. DIII-D is in a unique position to make high quality measurements of Y_Be_D in the actual tokamak environment, under well-controlled, well-diagnosed conditions - and without the uncertainties of the spectroscopic method for measuring atomic influx rates in a tokamak. The uncertainties in ion beam analysis are much smaller than the spectroscopic one	ITER IO Urgent Research Task :	Yes
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