Plasma impact on diagnostic mirrors in JET
(English)Manuscript (preprint) (Other academic)
All optical diagnostics in ITER will rely on metallic mirrors acting as plasma-facing components. This contribution provides a comprehensive account on plasma impact on diagnostic mirrors in JET with the ITER-Like Wall. Specimens from the First Mirror Test and the lithium-beam diagnostic have been studied by spectrophotometry, ion beam analysis and electron microscopy. Test mirrors made of molybdenum were retrieved from the main chamber and the divertor after exposure to the 2013-2014 experimental campaign. In the main chamber, only mirrors located at the entrance of the carrier lost reflectivity (Be deposition from the eroded limiters), while those located deeper in the carrier were only slightly affected. The performance of mirrors in the JET divertor was strongly degraded by deposition of beryllium, tungsten and other species. Mirrors from the lithium-beam diagnostic have been studied for the first time. Gold coatings were severely damaged by intense arcing. As a consequence, material mixing of the gold layer with the stainless steel substrate occurred. Total reflectivity dropped from over 90% to less than 60 %, i.e. to the level typical for stainless steel.
JET, First Mirror Test, diagnostic mirrors, erosion-deposition
Research subject Physics
IdentifiersURN: urn:nbn:se:kth:diva-190899OAI: oai:DiVA.org:kth-190899DiVA: diva2:953641
QC 201608192016-08-182016-08-182016-09-02Bibliographically approved