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Nitrogen removal from plasma-facing components by ion cyclotron wall conditioning in TEXTOR
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
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2015 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, 688-692 p.Article in journal (Other academic) Published
Abstract [en]

The efficiency of ion cyclotron wall conditioning (ICWC) in the removal of nitrogen from plasma-facing components in TEXTOR was assessed. In two experiments the wall was loaded with nitrogen and subsequently cleaned by ICWC in deuterium and helium. The retention and removal of nitrogen was studied in-situ by means of mass spectrometry, and ex-situ by surface analysis of a set of graphite, tungsten and TZM plates installed on test limiter systems. N-15 rare isotope was used as a marker. The results from the gas balance showed that about 25% of the retained nitrogen was removed after ICWC cleaning, whereas surface analysis of the plates based on ToF-HIERDA showed an increase of the deposited species after the cleaning. This indicates that during ICWC operation on carbon devices, nitrogen is not only pumped out but also transported to other locations on the wall. Additionally, deuterium surface content was studied before and after ICWC cleaning.

Place, publisher, year, edition, pages
2015. Vol. 463, 688-692 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-155184DOI: 10.1016/j.jnucmat.2014.11.113ISI: 000358467200144Scopus ID: 2-s2.0-84937731653OAI: oai:DiVA.org:kth-155184DiVA: diva2:760078
Funder
Swedish Research Council, 621-2012-4148
Note

Updated from "In press" to "Published". QC 20150901

Available from: 2014-11-03 Created: 2014-11-03 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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Rubel, Marek

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