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Plasma impact on diagnostic mirrors in JET
KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.ORCID-id: 0000-0001-5603-8559
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
Abstract [en]

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.

Emneord [en]
JET, First Mirror Test, diagnostic mirrors, erosion-deposition
HSV kategori
Forskningsprogram
Fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-190899OAI: oai:DiVA.org:kth-190899DiVA, id: diva2:953641
Merknad

QC 20160819

Tilgjengelig fra: 2016-08-18 Laget: 2016-08-18 Sist oppdatert: 2016-09-02bibliografisk kontrollert
Inngår i avhandling
1. Impact of material migration on plasma-facing components in tokamaks
Åpne denne publikasjonen i ny fane eller vindu >>Impact of material migration on plasma-facing components in tokamaks
2016 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Plasma-wall interaction plays an essential role in the performance and safety of a fusion reactor. This thesis focuses on the impact of material migration on plasma-facing components. It is based on experiments performed in tokamaks: JET, TEXTOR and ASDEX Upgrade. The objectives of the experiments were to assess fuel and impurity removal under ion cyclotron wall conditioning (ICWC) and plasma impact on diagnostic mirrors.

In wall conditioning studies, tracer techniques based on the injection of rare isotopes (15N, 18O) were used to determine conclusively the impact of the respective gases. For the first time, probe surfaces and wall components exposed to ICWC were examined by surface analysis methods. Discharges in hydrogen were the most efficient to erode carbon co-deposits, resulting in a reduction of the initial deuterium content by a factor of two. It was also found that impurities desorbed under ICWC are partly re-deposited on the wall.

Plasma impact on diagnostic mirrors was determined by surface analysis of test mirrors exposed at JET. Reflectivity of mirrors from the divertor region was severely decreased due to deposits of beryllium, deuterium, carbon and other impurities. This result points out the need to develop mirror maintenance procedures. Neutron damage on mirrors was simulated by ion irradiation in an ion implanter. It was shown that damage levels similar to those expected in the first wall of a fusion reactor do not produce a significant change in reflectivity.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2016. s. 54
Serie
TRITA-EE, ISSN 1653-5146
Emneord
Fusion, material migration, wall conditioning, diagnostic mirrors, plasma-facing materials
HSV kategori
Forskningsprogram
Fysik
Identifikatorer
urn:nbn:se:kth:diva-190903 (URN)978-91-7729-046-9 (ISBN)
Disputas
2016-09-15, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad

QC 20160819

Tilgjengelig fra: 2016-08-19 Laget: 2016-08-18 Sist oppdatert: 2016-08-19bibliografisk kontrollert

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