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Modelling the multifaceted physics of metallic dust and droplets in fusion plasmas
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-7796-1887
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plasma-material interaction constitutes one of the major scientific and technological issues affecting the development of thermonuclear fusion power plants. In particular, the release of metallic dust and droplets from plasmafacing components is a crucial aspect of reactor operation. By penetrating into the burning plasma, these micrometric particles act as a source of impurities which tend to radiate away the plasma energy, cooling it down below the threshold temperatures for sustainable fusion reactions. By accumulating in the reactor chamber, dust particles tend to retain fuel elements, lowering the reactor efficiency and increasing its radioactivity content. Dust accumulation also increases the risk of explosive hydrogen production upon accidental air or water ingress in the vacuum chamber. Numerical dust transport codes provide the essential framework to guide theoretical and experimental dust studies by simulating the intricate couplings between the many physical processes driving dust dynamics in fusion plasmas. This thesis reports on the development and validation of the MIGRAINe code, which specifically targets plasma-surface interaction processes and the physics of dust particles impinging on plasma-facing components to address long-term dust migration and accumulation in fusion devices.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , 80 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:084
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187638ISBN: 978-91-7729-041-4 (print)OAI: oai:DiVA.org:kth-187638DiVA: diva2:930798
Public defence
2016-06-13, E3, Osquars backe 14, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20160525

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-05-26Bibliographically approved
List of papers
1. Dust-wall and dust-plasma interaction in the MIGRAINe code
Open this publication in new window or tab >>Dust-wall and dust-plasma interaction in the MIGRAINe code
2014 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 9, 095005- p.Article in journal (Refereed) Published
Abstract [en]

The physical models implemented in the recently developed dust dynamics code MIGRAINe are described. A major update of the treatment of secondary electron emission, stemming from models adapted to typical scrape-off layer temperatures, is reported. Sputtering and plasma species backscattering are introduced from fits of available experimental data and their relative importance to dust charging and heating is assessed in fusion-relevant scenarios. Moreover, the description of collisions between dust particles and plasma-facing components, based on the approximation of elastic-perfectly plastic adhesive spheres, has been upgraded to take into account the effects of particle size and temperature.

Keyword
dust, MIGRAINe, dust-wall interaction, dust-wall collisions, transport
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-153857 (URN)10.1088/0741-3335/56/9/095005 (DOI)000341854100015 ()2-s2.0-84906569539 (Scopus ID)
Note

QC 20141010

Available from: 2014-10-10 Created: 2014-10-09 Last updated: 2017-12-05Bibliographically approved
2. Migration of tungsten dust in tokamaks: role of dust-wall collisions
Open this publication in new window or tab >>Migration of tungsten dust in tokamaks: role of dust-wall collisions
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2013 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 12, 123002- p.Article in journal (Refereed) Published
Abstract [en]

The modelling of a controlled tungsten dust injection experiment in TEXTOR by the dust dynamics code MIGRAINe is reported. The code, in addition to the standard dust-plasma interaction processes, also encompasses major mechanical aspects of dust-surface collisions. The use of analytical expressions for the restitution coefficients as functions of the dust radius and impact velocity allows us to account for the sticking and rebound phenomena that define which parts of the dust size distribution can migrate efficiently. The experiment provided unambiguous evidence of long-distance dust migration; artificially introduced tungsten dust particles were collected 120 degrees toroidally away from the injection point, but also a selectivity in the permissible size of transported grains was observed. The main experimental results are reproduced by modelling.

Keyword
Surface-Roughness, Theoretical-Model, Plastic Spheres, Oblique Impacts, Elastic Solids, Contact, Restitution, Adhesion, Textor, Coefficient
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-140162 (URN)10.1088/0029-5515/53/12/123002 (DOI)000327787000004 ()2-s2.0-84889008281 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20140121

Available from: 2014-01-21 Created: 2014-01-17 Last updated: 2017-12-06Bibliographically approved
3. Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration
Open this publication in new window or tab >>Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration
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2014 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 3, 035014- p.Article in journal (Refereed) Published
Abstract [en]

Experimental data on dust resident in the EXTRAP T2R reversed-field pinch are reported. Mobile dust grains are captured in situ by silicon collectors, whereas immobile grains are sampled post mortem from the wall by adhesive tape. The simulation of collection asymmetries by the MIGRAINe dust dynamics code in combination with the experimental results is employed to deduce some characteristics of the mechanism of intrinsic dust release. All evidence suggests that re-mobilization is dominant with respect to dust production.

Keyword
dust, collection, dust dynamics, MIGRAINe
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-143703 (URN)10.1088/0741-3335/56/3/035014 (DOI)000331896200014 ()2-s2.0-84894272951 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20140328

Available from: 2014-03-28 Created: 2014-03-27 Last updated: 2017-12-05Bibliographically approved
4. Elastic-plastic adhesive impacts of tungsten dust with metal surfaces in plasma environments
Open this publication in new window or tab >>Elastic-plastic adhesive impacts of tungsten dust with metal surfaces in plasma environments
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2015 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, 877-880 p.Article in journal (Refereed) Published
Abstract [en]

Dust-surface collisions impose size selectivity on the ability of dust grains to migrate in scrape-off layer and divertor plasmas and to adhere to plasma-facing components. Here, we report first experimental evidence of dust impact phenomena in plasma environments concerning low-speed collisions of tungsten dust with tungsten surfaces: re-bouncing, adhesion, sliding and rolling. The results comply with the predictions of the model of elastic-perfectly plastic adhesive spheres employed in the dust dynamics code MIGRAINe for sub- to several meters per second impacts of micrometer-range metal dust.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-172698 (URN)10.1016/j.jnucmat.2014.09.064 (DOI)000358467200187 ()2-s2.0-84937636637 (Scopus ID)
Note

QC 20150901

Available from: 2015-09-01 Created: 2015-08-27 Last updated: 2017-12-04Bibliographically approved
5. Fast camera observations of injected and intrinsic dust in TEXTOR
Open this publication in new window or tab >>Fast camera observations of injected and intrinsic dust in TEXTOR
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2015 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 12, 125017Article in journal (Refereed) Published
Abstract [en]

Stereoscopic fast camera observations of pre-characterized carbon and tungsten dust injection in TEXTOR are reported, along with the modelling of tungsten particle trajectories with MIGRAINe. Particle tracking analysis of the video data showed significant differences in dust dynamics: while carbon flakes were prone to agglomeration and explosive destruction, spherical tungsten particles followed quasi-inertial trajectories. Although this inertial nature prevented any validation of the force models used in MIGRAINe, comparisons between the experimental and simulated lifetimes provide a direct evidence of dust temperature overestimation in dust dynamics codes. Furthermore, wide-view observations of the TEXTOR interior revealed the main production mechanism of intrinsic carbon dust, as well as the location of probable dust remobilization sites.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015
Keyword
dust, fast camera, TRACE, MIGRAINe, TEXTOR
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-185679 (URN)10.1088/0741-3335/57/12/125017 (DOI)000373345000020 ()2-s2.0-84976381555 (Scopus ID)
Note

QC 20160425

Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2017-11-30Bibliographically approved
6. Interaction of adhered metallic dust with transient plasma heat loads
Open this publication in new window or tab >>Interaction of adhered metallic dust with transient plasma heat loads
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2016 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, 066010Article in journal (Refereed) Published
Abstract [en]

The first study of the interaction of metallic dust (tungsten, aluminum) adhered on tungsten substrates with transient plasma heat loads is presented. Experiments were carried out in the Pilot-PSI linear device with transient heat fluxes up to 550 MW m(-2) and in the DIII-D divertor tokamak. The central role of the dust-substrate contact area in heat conduction is highlighted and confirmed by heat transfer simulations. The experiments provide evidence of the occurrence of wetting-induced coagulation, a novel growth mechanism where cluster melting accompanied by droplet wetting leads to the formation of larger grains. The physical processes behind this mechanism are elucidated. The remobilization activity of the newly formed dust and the survivability of tungsten dust on hot surfaces are documented and discussed in the light of implications for ITER.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keyword
metallic dust, transient heat, dust remobilization, droplets
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-187635 (URN)10.1088/0029-5515/56/6/066010 (DOI)000376446000014 ()2-s2.0-84975476301 (Scopus ID)
Note

QC 20160620

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-06-08Bibliographically approved
7. Beryllium droplet cooling and distribution in the ITER vessel after a disruption
Open this publication in new window or tab >>Beryllium droplet cooling and distribution in the ITER vessel after a disruption
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2016 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326Article in journal (Refereed) Submitted
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-187637 (URN)
Note

QC 20160711

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-11-30Bibliographically approved

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