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Plasma-Facing Components in Tokamaks: Material Modification and Fuel Retention
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for the steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in this thesis in order to contribute to a better understanding and the development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in the Nuclear Research Center Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). Following issues were addressed: (a) properties of material migration products, i.e. co-deposited layers and dust particles; (b) impact of fuel removal methods on dust generation and on modification of plasma-facing components; (c) efficiency of fuel and deposit removal techniques; (d) degradation mechanism of diagnostic components - mirrors - and methods of their regeneration.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xiv, 58 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:058
Keyword [en]
magnetic confinement fusion, plasma-facing components, plasma-facing materials, fuel inventory, erosion and deposition
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-105099ISBN: 978-91-7501-567-5 (print)OAI: oai:DiVA.org:kth-105099DiVA: diva2:570022
Public defence
2012-12-12, F3, Lindstedtsvagen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121116

Available from: 2012-11-16 Created: 2012-11-16 Last updated: 2012-11-16Bibliographically approved
List of papers
1. Survey of dust formed in the TEXTOR tokamak: structure and fuel retention
Open this publication in new window or tab >>Survey of dust formed in the TEXTOR tokamak: structure and fuel retention
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2009 (English)In: Physica scripta. T, ISSN 0281-1847, Vol. T138, 014025- p.Article in journal (Refereed) Published
Abstract [en]

A detailed survey of erosion and deposition on plasma-facing components was performed in the TEXTOR tokamak. Co-deposits and dust particles were collected from graphite limiters and from several locations on the Inconel liner. The total amount of dust (loose material), originating mainly from carbon-rich co-deposits detached from the limiters and the liner, was around 2 g, with sizes from 0.1 mu m to 1 mm. The morphology and fuel retention was determined using microscopy methods, ion beam analysis and thermal desorption spectrometry. The study revealed differences in structure and fuel content between deposits from the toroidal and main poloidal limiters. There were also splashes, up to 1 mm in diameter, of molten metal (mainly nickel) on the toroidal limiters. Issues of the dust conversion factor (erosion-to-dust) are addressed and a comparison with results of previous dust surveys at TEXTOR is also briefly presented.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2009
Keyword
CONTROLLED FUSION DEVICES, CO-DEPOSITED LAYERS, PLASMA-FACING COMPONENTS, HIGH HEAT-FLUX, CARBON, PARTICLES, EROSION, ITER, CONSEQUENCES, EMISSION
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-25575 (URN)10.1088/0031-8949/2009/T138/014025 (DOI)000273199200026 ()2-s2.0-77953881798 (Scopus ID)
Conference
12th International Workshop on Plasma-Facing Materials and Components for Fusion Applications Julich, GERMANY, MAY, 2009
Note

QC 20101119

Available from: 2012-01-26 Created: 2010-10-27 Last updated: 2017-12-12Bibliographically approved
2. Laser-based and thermal methods for fuel removal and cleaning of plasma-facing components
Open this publication in new window or tab >>Laser-based and thermal methods for fuel removal and cleaning of plasma-facing components
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2011 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, S801-S804 p.Article in journal (Refereed) Published
Abstract [en]

The efficiency of two methods for in-situ fuel removal has been tested on carbon and tungsten limiters retrieved from the TEXTOR and Tore Supra tokamaks: laser-inducedablation of co-deposits and annealing in vacuum at elevated temperature. The analyses of gas phase and surfaces performed with thermal desorption spectrometry, optical spectroscopy, ion beam analysis, surface profilometry and microscopy methods have shown: (i) the ablation leads to the generation of dust particles of 50 nm – 2μm; (ii) volatile products of ablation undergo condensation on surrounding surfaces; (iii) D/C ratio in such condensate is in the range 0.02-0.03; (iv) long-term annealing of 623 K for 70 hours results in release of not more ~10 % of deuterium accumulated in plasma-facing components; (v) effective removal is reached by heating to 900-1300 K.

Keyword
carbon, ´first wall materials, hydrogen, laser, tungsten
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-29586 (URN)10.1016/j.jnucmat.2011.01.119 (DOI)000298128100183 ()2-s2.0-80054839170 (Scopus ID)
Note
Updated from in Press to Published. QC 20120227Available from: 2011-02-09 Created: 2011-02-09 Last updated: 2017-12-11Bibliographically approved
3. Fuel re-absorption by thermally treated co-deposited carbon layers
Open this publication in new window or tab >>Fuel re-absorption by thermally treated co-deposited carbon layers
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2011 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, 014006- p.Article in journal (Refereed) Published
Abstract [en]

Systematic studies have been conducted to address the fuel re-absorption by carbon deposits under repeated exposure to plasma after cleaning procedures. The investigation was done with graphite tiles from ALT-II (Advanced Limiter Test II), i.e. the main limiter at the TEXTOR tokamak. Pure graphite plates were used as the reference material. The experimental programme comprised the following: pre-characterization of specimens; D desorption by baking the tile at 1273 K; surface analyses of the fuel-depleted layers; exposure to deuterium in a laboratory plasma device and in TEXTOR; and quantitative assessment of deuterium re-absorption. The main result is that fuel retention in the re-exposed deposits is 30–40 times lower than that in the original co-deposit, showing that fuel re-absorption does not lead to an immediate re-saturation of deposits. Annealing at high temperatures enhances layer brittleness, leading eventually to detachment of co-deposits.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2011
Keyword
co-deposited layers, plasma-facing components, carbon, erosion, deposition, fuel retention, re-absorption
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-66730 (URN)10.1088/0031-8949/2011/T145/014006 (DOI)000298475200007 ()2-s2.0-84857612866 (Scopus ID)
Note
QC 20120127Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved
4. Efficiency of fuel removal techniques tested on plasma-facing components from the TEXTOR tokamak
Open this publication in new window or tab >>Efficiency of fuel removal techniques tested on plasma-facing components from the TEXTOR tokamak
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2012 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 87, no 5-6, 935-940 p.Article in journal (Refereed) Published
Abstract [en]

An overview of several techniques considered for fuel and co-deposits removal is given. The methods were tested both on plasma-facing components from the TEXTOR tokamak and on laboratory-prepared layers: (a) chemical approach based on oxidative or nitrogen-assisted plasma; (b) photonic methods with laser-induced fuel desorption or ablation of co-deposits; (c) thermal desorption in vacuum or under oxidative conditions at a broad range of temperatures. The emphasis is on outstanding issues associated with every technique aiming at the reduction of fuel content: the efficiency of fuel and co-deposit removal, the surface state of PFC following the treatment and dust generation.

Keyword
Fuel retention and removal, Laser-induced desorption, Nitrogen plasma, Oxidation, TEXTOR
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-104897 (URN)10.1016/j.fusengdes.2012.02.054 (DOI)000309781400105 ()2-s2.0-84865798988 (Scopus ID)
Note

QC 20121114

Available from: 2012-11-14 Created: 2012-11-14 Last updated: 2017-12-07Bibliographically approved
5. Comparison of JET main chamber erosion with dust collected in the divertor
Open this publication in new window or tab >>Comparison of JET main chamber erosion with dust collected in the divertor
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2013 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 436, no Suppl., 827-832 p.Article in journal (Refereed) Published
Abstract [en]

A complete global balance for carbon in JET requires knowledge of the net erosion in the main chamber, net deposition in the divertor and the amount of dust and flakes collecting in the divertor region. This paper describes a number of measurements on aspects of this global picture. Profiler measurements and cross section microscopy on tiles that were removed in the 2009 JET intervention are used to evaluate the net erosion in the main chamber and net deposition in the divertor. In addition the mass of dust and flakes collected from the JET divertor during the same intervention is also reported and included as part of the balance. Spectroscopic measurements of carbon erosion from the main chamber are presented and compared with the erosion measurements for the main chamber.

Keyword
Carbon erosion, Divertor region, Dust collected, Erosion measurements, Jet Divertors, Profiler measurements, Spectroscopic measurements
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-105157 (URN)10.1016/j.jnucmat.2013.01.179 (DOI)000330795300177 ()2-s2.0-84885483967 (Scopus ID)
Conference
20th International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI), Forschungszentrum Julich, Aachen, Germany, May 21-25, 2012
Note

Updated from "Submitted" to "Published". QC 20140120

Available from: 2012-11-16 Created: 2012-11-16 Last updated: 2017-12-07Bibliographically approved
6. Removal of beryllium-containing films deposited in JET from mirror surfaces by laser cleaning
Open this publication in new window or tab >>Removal of beryllium-containing films deposited in JET from mirror surfaces by laser cleaning
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2011 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, ISSN 0022-3115, Vol. 415, no 1, S1199-S1202 p.Article in journal (Refereed) Published
Abstract [en]

A set of stainless steel (SS) and molybdenum mirror samples located in the divertor and at the outer mid-plane of the vessel were exposed in JET from 2005 to 2007. A selection of these mirror samples with well adhered deposits (i.e. not flaking) of up to a few hundred nanometers in thickness and with Be/C ratios ranging from 0 to similar to 1 have been cleaned using a laser system developed at CEA, Saclay. Following laser cleaning the recovered reflectivity was generally better in the infrared than the visible spectrum, with recovery of up to 90% of the initial reflectivity being obtained at 1600 nm for both Mo and SS mirrors falling as low as 20-30% of initial reflectivity at a wavelength of 400 nm for some SS mirrors, rising to similar to 80% for Mo mirrors. Some deposit remained on the mirrors after the cleaning trials.

Keyword
Cleaning trials, Laser cleaning, Laser systems, Mirror surfaces, Visible spectra
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-29587 (URN)10.1016/j.jnucmat.2010.11.076 (DOI)000298128100273 ()2-s2.0-80054843301 (Scopus ID)
Conference
19th International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI), May 24-28, 2010,Univ Calif, Gen Atom, San Diego, CA
Note

QC 20110209

Available from: 2011-02-09 Created: 2011-02-09 Last updated: 2017-12-11Bibliographically approved
7. Overview of Fuel Removal Methods from Plasma-Facing Components
Open this publication in new window or tab >>Overview of Fuel Removal Methods from Plasma-Facing Components
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2011 (English)In: 38th EPS Conference on Plasma Physics, 2011Conference paper, Published paper (Refereed)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-66781 (URN)2-s2.0-84867653845 (Scopus ID)
Conference
38th EPS Conference on Plasma Physics. Strasbourg. 27th June - 1st July 2011
Note
QC 20120127Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2012-11-16Bibliographically approved
8. Assessment of cleaning methods for rst mirrors tested in JET for ITER
Open this publication in new window or tab >>Assessment of cleaning methods for rst mirrors tested in JET for ITER
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(English)Article in journal (Other academic) Submitted
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-105161 (URN)
Note

QS 2012

Available from: 2012-11-16 Created: 2012-11-16 Last updated: 2012-11-16Bibliographically approved

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Output format
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