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An overview of the comprehensive First Mirror Test in JET with ITER-like wall
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0001-9901-6296
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
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2014 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, 014011- p.Article in journal (Refereed) Published
Abstract [en]

The First Mirror Test in Joint European Torus (JET) with the International Thermonuclear Experimental Reactor-like wall was performed with polycrystalline molybdenum mirrors. Two major types of experiments were done. Using a reciprocating probe system in the main chamber, a short-term exposure was made during a 0.3 h plasma operation in 71 discharges. The impact on reflectivity was negligible. In a long-term experiment lasting 19 h with 13 h of X-point plasma, 20 Mo mirrors were exposed, including four coated with a 1 mu m-thick Rh layer. Optical performance of all mirrors exposed in the divertor was degraded by up to 80% because of beryllium, carbon and tungsten co-deposits on surfaces. Total reflectivity of most Mo mirrors facing plasma in the main chamber was only slightly affected in the spectral range 400-1600 nm, while the Rh-coated mirror lost its high original reflectivity by 30%, thus decreasing to the level typical of molybdenum surfaces. Specular reflectivity was decreased most strongly in the 250-400 nm UV range. Surface measurements with x-ray photoelectron spectroscopy and depth profiling with secondary ion mass spectrometry and heavy-ion elastic recoil detection analysis (ERDA) revealed that the very surface region on both types of mirrors had been modified by neutrals, resulting eventually in the composition change: Be, C, D at the level below 1x10(16) cm(-2) mixed with traces of Ni, Fe in the layer 10-30 nm thick. On several exposed mirrors, the original matrix material (Mo) remained as the major constituent of the modified layer. The data obtained in two major phases of the JET operation with carbon and full metal walls are compared. The implications of these results for first mirrors and their maintenance in a reactor-class device are discussed.

Place, publisher, year, edition, pages
2014. Vol. T159, 014011- p.
Keyword [en]
diagnostic mirrors, surface analysis, reflectivity, erosion and deposition, JET, ITER-like wall
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-145842DOI: 10.1088/0031-8949/2014/T159/014011ISI: 000334847800012Scopus ID: 2-s2.0-84902125224OAI: oai:DiVA.org:kth-145842DiVA: diva2:720644
Conference
14th International Conference on Plasma-Facing Materials and Components for Fusion Applications, PFMC 2013; Julich; Germany; 13 May 2013 through 17 May 2013
Funder
Swedish Research Council, 621-2009-4138 621-2012-4148
Note

QC 20140602

Available from: 2014-06-02 Created: 2014-06-02 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Plasma-Facing Components in Tokamaks: Studies of Wall Conditioning Processes and Plasma Impact on Diagnostic Mirrors
Open this publication in new window or tab >>Plasma-Facing Components in Tokamaks: Studies of Wall Conditioning Processes and Plasma Impact on Diagnostic Mirrors
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding of material migration and its impact on the formation of co-deposited mixed material layers on plasma-facing components is essential for the development of fusion reactors. This thesis focuses on this topic. It is based on experiments performed at JET and TEXTOR tokamaks. The major objectives were to determine: (i) fuel and impurity removal from plasma-facing components by ICWC in different gas mixtures, (ii) fuel and impurity transport connected to ICWC operation, (iii) plasma impact on diagnostic mirrors. All these issues are in line with the ITER needs: mitigation of co-deposition and fuel inventory, and the performance of first mirrors in long-term operation. The novelty in research is demonstrated by several elements. In wall conditioning studies, tracer techniques based on injection of rare isotopes (N-15, O-18) were used to determine conclusively the impact of respective gases. Also, a new approach to ICWC was developed by combining global gas balance studies based on mass spectrometry and the use of multiple surface probes exposed to discharges and then studied ex-situ with accelerator-based techniques. Impact of plasma on diagnostic mirrors was determined after exposure to the entire first experimental campaign in JET-ILW.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiv, 44 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2014:060
Keyword
Plasa-wall interactions, wall conditioning, tracers, diagnostic mirrors, ICWC
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-154621 (URN)978-91-7595-309-0 (ISBN)
Presentation
2014-11-07, Seminar room, Teknikringen 31, KTH- Royal Institute of Technology, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141103

Available from: 2014-11-03 Created: 2014-10-26 Last updated: 2014-11-03Bibliographically approved
2. Impact of material migration on plasma-facing components in tokamaks
Open this publication in new window or tab >>Impact of material migration on plasma-facing components in tokamaks
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 54 p.
Series
TRITA-EE, ISSN 1653-5146
Keyword
Fusion, material migration, wall conditioning, diagnostic mirrors, plasma-facing materials
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-190903 (URN)978-91-7729-046-9 (ISBN)
Public defence
2016-09-15, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160819

Available from: 2016-08-19 Created: 2016-08-18 Last updated: 2016-08-19Bibliographically approved

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