Plasma impact on diagnostic mirrors in JET

• Published in: Nuclear materials and energy 2017-08, Vol.12, p.506-512
• Main Authors: Garcia-Carrasco, A., Petersson, P., Rubel, M., Widdowson, A., Fortuna-Zalesna, E., Jachmich, S., Brix, M., Marot, L.
• Format: Article
• Language: English
• Subjects: Diagnostic mirrors; Erosion-deposition; First mirror test; JET
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2016.12.032

•Results of the First Mirror Test for the 2013–2014 campaign at JET are presented.•Reflectivity of mirrors from the divertor was severely degraded.•Metallic splashes were identified on mirror surfaces in the main chamber.•Li-beam diagnostic mirrors at JET were studied for the first time.•Gold coating of the Li-beam diagnostic mirrors was severely damaged by arcing Metallic mirrors will be essential components of all optical systems for plasma diagnosis in ITER. 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), 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.