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Ageing of structural materials in tokamaks: TEXTOR liner study
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-1062-8101
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
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2017 (English)In: Physica scripta. T, ISSN 0281-1847Article in journal, Meeting abstract (Refereed) Submitted
Abstract [en]

After the final shut-down of the tokamak TEXTOR, all of its machine parts became accessible for comprehensive studies. This unique chance enabled the study of the Inconel 625 liner by a wide range of methods. The aim was to evaluate eventual alteration of surface and bulk characteristics from recessed wall elements that may influence the machine performance. The surface was covered with stratified layers consisting mainly of boron, carbon, oxygen, and in some cases also silicon. Wall conditioning and limiter materials hence predominantly define deposition on the liner. Deposited layers on recessed wall elements reach micrometre thickness within decades, peel off and may contribute to the dust inventory in tokamaks. Fuel retention was about 4 at% of the overall layers, with no evidence for diffusion into the Inconel substrate. Inconel 625 retained its mechanical strength despite 26 years of cyclic heating, stresses and particle bombardment.

Place, publisher, year, edition, pages
2017.
Keyword [en]
Fusion, Plasma-Wall Interaction, Fuel Retention, Inconel, Dust
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-210415OAI: oai:DiVA.org:kth-210415DiVA: diva2:1118352
Conference
16th International Conference on Plasma-Facing Materials and Components for Fusion Applications, 16th - 19th May 2017, Neuss/Düsseldorf, Germany
Note

QC 20170630

Available from: 2017-06-30 Created: 2017-06-30 Last updated: 2017-06-30Bibliographically approved
In thesis
1. Material migration in tokamaks: Erosion-deposition patterns and transport processes
Open this publication in new window or tab >>Material migration in tokamaks: Erosion-deposition patterns and transport processes
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Controlled thermonuclear fusion may become an attractive future electrical power source. The most promising of all fusion machine concepts is called a tokamak. The fuel, a plasma made of deuterium and tritium, must be confined to enable the fusion process. It is also necessary to protect the wall of tokamaks from erosion by the hot plasma. To increase wall lifetime, the high-Z metal tungsten is foreseen as wall material in future fusion devices due to its very high melting point. This thesis focuses on the following consequences of plasma impact on a high-Z wall: (i) erosion, transport and deposition of high-Z wall materials; (ii) fuel retention in tokamak walls; (iii) long term effects of plasma impact on structural machine parts; (iv) dust production in tokamaks.

An extensive study of wall components has been conducted with ion beam analysis after the final shutdown of the TEXTOR tokamak. This unique possibility offered by the shutdown combined with a tracer experiment led to the largest study of high-Z metal migration and fuel retention ever conducted. The most important results are:

 

- transport is greatly affected by drifts and flows in the plasma edge;

- stepwise transport along wall surfaces takes place mainly in the toroidal direction;

- fuel retention is highest on slightly retracted wall elements;

- fuel retention is highly inhomogeneous.

 

A broad study on structural parts of a tokamak has been conducted on the TEXTOR liner. The plasma impact does neither degrade mechanical properties nor lead to fuel diffusion into the bulk after 26 years of duty time. Peeling deposition layers on the liner retain fuel in the order of 1g and represent a dust source. Only small amounts of dust are found in TEXTOR with overall low deuterium content. Security risks in future fusion devices due to dust explosions or fuel retention in dust are hence of lesser concern.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 109 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2017:060
Keyword
TEXTOR, fusion, plasma physics, transport, migration, tracers, tokamak, limiter, divertor, high-Z, ion beam analysis, Rutherford backscattering, Nuclear reaction analysis, Elastic recoil detection analysis
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-209758 (URN)978-91-7729-461-0 (ISBN)
Public defence
2017-09-19, F3, Lindstedtsvägen 26, Stockholm, 14:59 (English)
Opponent
Supervisors
Note

QC 20170630

Available from: 2017-06-30 Created: 2017-06-22 Last updated: 2017-06-30Bibliographically approved

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