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Laser-based and thermal methods for fuel removal and cleaning of plasma-facing components
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9901-6296
Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
Institute for Energy Research, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany.
Show others and affiliations
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.

Place, publisher, year, edition, pages
2011. Vol. 415, no 1, S801-S804 p.
Keyword [en]
carbon, ´first wall materials, hydrogen, laser, tungsten
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-29586DOI: 10.1016/j.jnucmat.2011.01.119ISI: 000298128100183Scopus ID: 2-s2.0-80054839170OAI: oai:DiVA.org:kth-29586DiVA: diva2:396260
Note
Updated from in Press to Published. QC 20120227Available from: 2011-02-09 Created: 2011-02-09 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Fuel retention and fuel removal from first wall components in tokamaks
Open this publication in new window or tab >>Fuel retention and fuel removal from first wall components in tokamaks
2011 (English)Licentiate 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 a steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in the on-going Ph.D. work in order to contribute to the better understanding and 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 Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom).

 This thesis provides an account on studies of fuel removal techniques from plasmafacing components (PFCs) and on consequences of dust formation. Following issues are addressed: (a)  properties of carbon and metal dust formed in the TEXTOR tokamak;  (b)  dust generation associated with removal of fuel and co-deposited layers from carbon PFCs from TEXTOR and Tore Supra;  (c)  surface morphology of wall components after different cleaning treatments;  (d)  surface properties of diagnostic mirrors tested at JET for ITER. The study dealt with carbon, tungsten and beryllium, i.e. with the three major elements being used for PFC in present-day devices and foreseen for a next-step machine.

 Some essential results are summarised by the following.

 (i)  The amount of loose dust found on the floor of the TEXTOR liner does not exceed 2 grams with particle size range 0.1 mm – 1 mm. The presence of fine (up to 1 mm) crystalline graphite in the collected matter suggests that brittle destruction of carbon PFC could take place during off-normal events. Carbon is the main component, but there are also magnetic and non-magnetic metal agglomerates. The results obtained strongly indicate that in a carbon wall machine the disintegration of flaking co-deposits on PFC is the main source of dust:  (ii)  The fuel content in dust and co-deposits varies from 10% on the main limiters to 0.03% on the neutralizer plates as determined by thermal desorption and ionbeam methods:  (iii)  Fuel removal by annealing in vacuum or by oxidative methods disintegrates codeposits. In the case of thick layers, the treatment makes them brittle thus reducing the adherence to the target and, as a consequence, this leads to the formation of dust:  (iv)   Application of thermal methods for fuel removal from carbon-rich layers is effective only at high temperatures (above 800 K), i.e. in the range exceeding the allowed baking temperature of the ITER divertor:  (v)   Photonic cleaning by laser pulses effectively removes fuel-rich deposited layers, but it also produces debris, especially under ablation conditions:  (vi)  Photonic cleaning of mirrors exposed in JET results in partial recovery of reflectivity, but surfaces are modified by laser pulses.

The presentation of results is accompanied by a discussion of their consequences for the future development and the application of fuel and dust removal methods in a next-step fusion device.

Place, publisher, year, edition, pages
Stockholm: KTH, 2011. ix, 40 p.
Series
Trita-EE, ISSN 1653-5146 ; 2011:011
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-29588 (URN)978-91-7415-867-0 (ISBN)
Note
QC 20110209Available from: 2011-02-09 Created: 2011-02-09 Last updated: 2011-03-10Bibliographically approved
2. Plasma-Facing Components in Tokamaks: Material Modification and Fuel Retention
Open this publication in new window or tab >>Plasma-Facing Components in Tokamaks: Material Modification and Fuel Retention
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
magnetic confinement fusion, plasma-facing components, plasma-facing materials, fuel inventory, erosion and deposition
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-105099 (URN)978-91-7501-567-5 (ISBN)
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

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