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Tracer techniques for the assessment of material migration and surface modification of plasma-facing components
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9901-6296
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0003-1062-8101
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9299-3262
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, 280-284 p.Article in journal (Refereed) Published
Abstract [en]

Tracer techniques were used in the TEXTOR tokamak to determine high-Z metal migration and the deposition of species used for plasma edge cooling or wall conditioning under different types of operation conditions. Volatile molybdenum hexa-fluoride, nitrogen-15 and oxygen-18 were used as markers in tokamak or ion cyclotron wall conditioning discharges (ICWC). The objective was to obtain qualitative and quantitative of a global and local deposition pattern and material mixing effects. The deposition and retention was studied on plasma-facing components, collector probes and test limiters. Optical spectroscopy and ex-situ analysis techniques were used to determine the plasma response to tracer injection and the modification of surface composition. Molybdenum and light isotopes were detected on all types of limiters and short-term probes retrieved from the vessel showing that both helium and nitrogen are trapped following wall conditioning and edge cooling. Only small amounts below 1 x 10(19) m(-2) of O-18 were detected on surfaces treated by oxygen-assisted ICWC.

Place, publisher, year, edition, pages
Elsevier, 2015. Vol. 463, 280-284 p.
National Category
Materials Engineering Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-172689DOI: 10.1016/j.jnucmat.2014.11.074ISI: 000358467200052Scopus ID: 2-s2.0-84937517699OAI: oai:DiVA.org:kth-172689DiVA: diva2:850225
Funder
Swedish Research Council, 621-2009-4138
Note

QC 20150901

Available from: 2015-09-01 Created: 2015-08-27 Last updated: 2017-06-30Bibliographically approved
In thesis
1. Material migration in tokamaks: Studies of deposition processes and characterisation of dust particles
Open this publication in new window or tab >>Material migration in tokamaks: Studies of deposition processes and characterisation of dust particles
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thermonuclear fusion may become an attractive future power source. The most promising of all fusion machine concepts is the tokamak. Despite decades of active research, still huge tasks remain before a fusion power plant can go online. One of these important tasks deals with the interaction between the fusion plasma and the reactor wall. This work focuses on how eroded wall materials of different origin and mass are transported in a tokamak device. Element transport can be examined by injection of certain species of unique and predetermined origin, so called tracers. Tracer experiments were conducted at the TEXTOR tokamak before its final shutdown. This offered an unique opportunity for studies of the wall and other internal components: For the first time it was possible to completely dismantle such a machine and analyse every single part of reactor wall, obtaining a detailed pattern of material migration. Main focus of this work is on the high-Z metals tungsten and molybdenum, which were introduced by WF6 and MoF6 injection into the TEXTOR tokamak in several material migration experiments. It is shown that Mo and W migrate in a similar way around the tokamak and that Mo can be used as tracer for W transport. It is further shown how other materials - medium-Z (Ni), low-Z (N-15 and F), fuel species (D) - migrate and get deposited. Finally, the outcome of dust sampling studies is discussed. It is shown that dust appearance and composition depends on origin, formation conditions and that it can originate even from remote systems like the NBI system. Furthermore, metal splashes and droplets have been found, some of them clearly indicating boiling processes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 80 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:102
Keyword
tokamak, fusion, plasma, material migration, particle transport, TEXTOR, PWI, plasma-wall interaction, plasma facing components, PFC, PFM, plasma facing materials, ALT limiter, MoF6, tracer experiment, molybdenum hexafluoride, future energy source, fuel retention, deuterium retention
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-178026 (URN)978-91-7595-766-1 (ISBN)
Presentation
2015-12-15, Seminarierummet på plan 3, Teknikringen 31, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20151203

Available from: 2015-12-03 Created: 2015-12-02 Last updated: 2016-10-26Bibliographically approved
2. 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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Rubel, MarekWeckmann, ArminStröm, Petter

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