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Title	70: DIMES test of misaligned CFC tile to establish size of misalignment needed to disrupt ITER
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,	ITPA Joint Experiment :	No
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. There will be 200,000 tiles in the ITER divertor. Off-normal events, e.g. disruptions, could cause tile misalignment. AUG and C-mod have shown that a small, 0.3 mm, misalignment of a single W-tile causes disruptions. It is assumed, but has never been demonstrated, that comparable - or even larger - misalignments of CFC tiles will not cause disruptions when exposed to the same power loading. It is important to confirm experimentally that this expectation is valid and to establish how large a misalignment of a CFC tile will likely cause a disruption in ITER. It is proposed to carry out DiMES tests with an intentionally misaligned CFC-tile to establish how large a misalignment is required to cause a disruption.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	High power, ELMing H-mode, USN discharge. The bottom separatrix slowly lowered onto DiMES with a CFC cap having a 1 mm high edge, X 1 cm wide X 1 cm long, simulating a mm misaligned tile. If the plasma does not disrupt, replace the DiMES sample with a higher exposed edge. Use several discharges with DiMES sample removed for measurements after each shot, to establish how the surface profile evolves through the exposures, i.e. does it "fire polish" as is known to happen with isotropic graphite, or do jagged CFC surfaces persist? The latter might not cause disruptions but could cause unacceptably high rates of carbon release into the plasma.
Background:	The carbon blooms in JET, TFTR were due to tile misalignments and sometimes caused disruptions: "If a carbon bloom occurs near the density limit during belt limiter operation on JET, a MARFE usually appears on the small major radius side of the plasma column. The MARFE does not usually result in a disruption even though the radiated power is nearly equal to the input power." Mike Ulrickson, Journal of Nuclear Materials 176 & 177 (1990) 44. CFC may be more problematic than isotropic carbon: extreme thermal stresses may cause the CFC to disintegrate, with fragments of significant size then penetrating the confined plasma, potentially causing a disruption.
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