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Modelling of deposition and erosion of injected WF6 and MoF6 in TEXTOR
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0003-1062-8101
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2016 (English)In: Nuclear Materials and Energy, ISSN 2352-1791Article in journal (Refereed) Published
Abstract [en]

Tracer injection experiments in TEXTOR with MoF 6 and WF 6 lead to local deposition of about 6% for Mo and about 1% for W relative to the injected amount of Mo and W atoms. Modelling of these experiments has been done with ERO applying updated data for physical sputtering. The dissociation of the injected molecules has been treated in a simplified manner due to the lack of dissociation rate coefficients. How- ever, with this it was possible to reproduce the observed radial penetration of Mo and W atoms into the plasma. The modelled local deposition efficiencies are about 50% for Mo and 60% for W assuming typical plasma parameters for the experimental conditions used. To reproduce the measured deposition efficien- cies an enhancement factor for the erosion of deposited Mo and W has to be assumed ( ∼10 for Mo and ∼25 for W). Due to the rather low electron temperature T e of these plasma conditions (T e ∼15 eV at the location of injection), Mo and W are mostly sputtered by impurities whereas sputtering due to deuterium is negligible. A parameter study applying larger electron temperature leads to increased sputtering and thus to reduced local deposition efficiencies of about 30% for Mo and 5% for W. Though, even under these conditions enhanced erosion, albeit with reduced enhancement factors, is needed in the modelling to obtain the small measured deposition efficiencies.

Place, publisher, year, edition, pages
Elsevier, 2016.
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-210416DOI: 10.1016/j.nme.2016.10.022ISI: 000417293300089Scopus ID: 2-s2.0-85007022634OAI: oai:DiVA.org:kth-210416DiVA, id: diva2:1118359
Conference
22nd International Conference on Plasma Surface Interactions in Controlled Fusion Devices, 30th May - 3rd June 2016, Rome, Italy
Note

QC 20170630

Available from: 2017-06-30 Created: 2017-06-30 Last updated: 2018-12-06Bibliographically 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. p. 109
Series
TRITA-EE, ISSN 1653-5146 ; 2017:060
Keywords
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)
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Note

QC 20170630

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

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