Comprehensive First Mirror Test for ITER at JET with Carbon Walls

• Metallic mirrors will be essential components of all optical spectroscopy and imaging systems forplasma diagnosis that will be used on the next-step magnetic fusion experiment, ITER. Any change of the mirrorperformance, in particular reflectivity, will influence the quality and reliability of detected signals. On therequest of the ITER Design Team, a First Mirror Test (FMT) has been carried out at JET during campaigns in2005-2007 and 2008-2009. To date, it has been the most comprehensive test performed with a large number oftest mirrors exposed in an environment containing both carbon and beryllium; the total plasma time (in 2005-2007 period) over 35 h including 27 h of X-point operation. 32 stainless steel and polycrystalline molybdenumflat-front and 45oangled mirrors were installed in separate channels of cassettes on the outer wall and in the MkII HD divertor: inner leg, outer leg and base plate under the load bearing tile. Post exposure studies comprisedreflectivity measurements and surface analyses with microscopy, secondary ion mass spectrometry, ion beamanalysis and energy dispersive X-ray spectroscopy.. The essential results are: (i) on the outer wall highreflectivity (~90%) is maintained for mirrors close to the channel entrance but it is degraded by 30-40 % deeperin the channel (ii) reflectivity loss by 70-90% is measured for mirrors placed in the divertor: outer, inner andbase; (iii) deuterium and carbon are the main elements detected on all mirror surfaces and the presence ofberyllium is also found; (iv) thick deposits show rough columnar structure and thickness is 1-20 μm; (v) bubblelike structures are detected in deposits; (vi) the deposition in channels in the divertor cassettes is pronounced atthe very entrance; (vii) photonic cleaning with laser removes deposits but the surface is damaged by laser pulses.In summary, reflectivity of all tested mirrors is degraded either by erosion with CX neutrals or by the formationof thick deposits. The implications of results obtained for first mirrors in next-step device are discussed andcritical assessment of various methods for in-situ cleaning of mirrors is presented. The conclusion is thatengineering solutions should be developed in order to install shutters or to implement a cassette with mirrors toreplace periodically the degraded ones

Ämnesord

NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

Publikations- och innehållstyp

ref (ämneskategori)

kon (ämneskategori)