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AbstractAbstract
[en] Tokamaks aim at producing energy by thermonuclear fusion heating a hydrogen plasma up to 150 million K and confining it with an intense magnetic field created by magnets carrying important currents. Superconductivity is a very valuable asset in this field since it allows to reduce the size of the magnets and their energy consumption in exchange for cooling them down to cryogenic temperatures. However, in tokamaks, magnetic field variations occur (e.g. due to the central solenoid discharge) and generate induction losses in the magnets. If their temperature increases too much, they lose their superconducting properties in a brutal transition called 'quench': to protect their integrity, they are then discharged and the magnetic confinement of the plasma is lost. We have therefore focused on the modeling of these losses - more precisely on the 'coupling losses' - since their knowledge is crucial to safely adapt the cryogenic cooling of the magnets and predict the operating limits of the tokamak. In order to both enhance the physical understanding of this complex phenomenon and provide simple but realistic solutions that can easily be integrated in multiphysics platforms already heavily solicited by the modeling of other effects, we have chosen to adopt an analytical approach on this problem. The cables commonly considered for tokamaks presenting a rather complex architecture (several hundreds of strands twisted together in specific patterns), we have carried out analytical and experimental studies at the different scales of the cable; we then compare the results of our approach to other existing ones (e.g. numerical models) and, when possible, to the experiment. (author)
[fr]
Les tokamaks visent a produire de l'energie par fusion thermonucleaire en chauffant un plasma d'hydrogene jusqu'a 150 millions K et en le confinant a l'aide d'un champ magnetique intense cree par des aimants transportant d'importants courants. La supraconductivite est un atout precieux ici car permettant de reduire la taille des aimants et leur consommation energetique en contrepartie d'un refroidissement cryogenique. Cependant, dans les tokamaks, des variations de champ magnetique apparaissent (ex: decharge du solenoide central) et generent des pertes par induction dans les aimants. Si leur temperature augmente trop, ils peuvent perdre leur etat supraconducteur lors d'une transition brutale appelee 'quench': afin de les proteger, ils sont decharges de leur courant entrainant ainsi la perte du plasma. Nous avons concentre notre travail sur la modelisation de ces pertes car leur connaissance est cruciale pour le bon dimensionnement du refroidissement des aimants et la prediction des limites operationnelles du tokamak. Afin d'ameliorer la comprehension physique de ce phenomene complexe et de proposer des solutions simples mais realistes, facilement integrables dans des plateformes multiphysiques deja fortement sollicitees par la modelisation d'autres effets, nous avons choisi d'adopter une approche analytique. Les cables presents dans les tokamaks ayant une architecture assez complexe (centaines de brins torsades ensemble), nous avons mene des etudes analytiques et experimentales aux differentes echelles du cable; nous comparons ensuite les resultats de notre approche a ceux d'autres modeles existants (ex: numeriques) et, lorsque cela est possible, a l'experience.Original Title
Courants d'ecrantage magnetique et pertes par couplage induites dans les aimants supraconducteurs pour la fusion thermonucleaire
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1 Dec 2017; 265 p; 52 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Sciences de l'Ingenieur, Energetique
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Report
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Thesis/Dissertation
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