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Le réacteur thermonucléaire expérimental international, ou ITER (acronyme de l'anglais International thermonuclear experimental reactor, également mot latin signifiant « chemin » ou « voie »), est un projet international de réacteur nucléaire de recherche civil à fusion nucléaire de type tokamak, situé à proximité immédiate du centre d’études nucléaires de Cadarache à Saint-Paul-lez-Durance (Bouches-du-Rhône, France). Le projet de recherche s'inscrit dans une démarche à long terme visant à l'industrialisation de la fusion nucléaire. Il associe trente-cinq pays : ceux de l'Union européenne ainsi que l'Inde, le Japon, la Chine, la Russie, la Corée du Sud et les États-Unis, ainsi que la Suisse et le Royaume-Uni en tant qu'États associés à la Communauté européenne de l'énergie atomique. ITER est le plus grand projet scientifique mondial actuel. Par sa complexité, son ambition et son budget hors-norme, ce projet de haute technologie a été comparé au programme Apollo. Il est sujet à de nom

Free-Boundary Simulations of ITER Advanced Scenarios

Karim Besseghir

The successful operation of ITER advanced scenarios is likely to be a major step forward in the development of controlled fusion as a power production source. ITER advanced scenarios raise specific challenges that are not encountered in presently-operated tokamaks. In this thesis, it is argued that ITER advanced operation may benefit from optimal control techniques. Optimal control ensures high performance operation while guaranteeing tokamak integrity. The application of optimal control techniques for ITER operation is assessed and it is concluded that robust optimisation is appropriate for ITER operation of advanced sce- narios. Real-time optimisation schemes are discussed and it is concluded that the necessary conditions of optimality tracking approach may potentially be appropriate for ITER operation, thus offering a viable closed-loop optimal control approach. Simulations of ITER advanced operation are necessary in order to assess the present ITER design and uncover the main difficulties that may be encountered during advanced operation. The DINA-CH&CRONOS full tokamak simulator is used to simulate the operation of the ITER hybrid and steady-state scenarios. It is concluded that the present ITER design is appropriate for performing a hybrid scenario pulse lasting more than 1000s, with a flat-top plasma current of 12MA, and a fusion gain of Q ∼= 8. Similarly, a steady-state scenario without internal transport barrier, with a flat-top plasma current of 10MA, and with a fusion gain of Q ∼= 5 can be realised using the present ITER design. The sensitivity of the advanced scenarios with respect to transport models and physical assumption is assessed using CRONOS. It is concluded that the hybrid scenario and the steady- state scenario are highly sensitive to the L-H transition timing, to the value of the confinement enhancement factor, to the heating and current drive scenario during ramp-up, and, to a lesser extent, to the density peaking and pedestal pressure.

EPFL2013

Irreversible Degradation in Nb3Sn Cable in Conduit Conductors

Ciro Calzolaio

One of the biggest goals for the international thermonuclear experimental reactor (ITER) is the steady state operation. For this reason all its coils will be superconducting and Nb3Sn material is used for both the toroidal field (TF) and the central solenoid (CS) coils. The primary current carrying unit in a coil is the cable, which contains hundreds of superconducting strands. The ITER coils will be made using a kind of cable called cable in conduit conductor (CICC). Both CS and TF magnets have to withstand several electromagnetic (EM) cycles in their lifetime. This has been discovered to cause a severe reduction of the magnet performances. Nb3Sn is a brittle material, therefore it is very strain sensitive. The knowledge of the strain state in a CICC allows the explanation of the performances of the cable itself, providing also information regarding the permanent damaging of the Nb3Sn structure. The measurement of the Nb3Sn strain state in a CICC is a very challenging task because it is not possible to make it directly. An indirect technique that allows the measurement of the thermal strain through the measurement of the magnetic susceptibility vs. temperature (χ(T )) for a CICC has been developed. A CICC is a complex system and as such it behaves in a way which is not directly predictable studying the single components. The elastic deformation of the superconducting layers produces reversible phenomena which interact with irreversible phenomena due to Nb3Sn fractures and to plastic deformations of the matrix surrounding the superconducting layers. Reversible and irreversible phenomena occurs together and are deeply shuffled such that it is not straightforward the explanation of the cable performance. The magnetic susceptibility measurements, via an appropriate data analysis, allow to quantify and to separate the thermal strain from the jumble of parameters necessary to describe the cable performance. Several TF and CS samples have been measured with this technique in the SULTAN test facility. Each cable behaves differently from the others but at least it is possible to identify common features. For some samples, the evolution of the performance with the EM cycles is dominated by reversible rearrangements of the strand position in the cable and consequently by the change of the strain distribution during the EM load, for others it is dominated by breakages and irreversible phenomena.

EPFL2013

Irreversible Degradation in Nb3Sn Cable in Conduit Conductors

Ciro Calzolaio

EPFL2013

Free-Boundary Simulations of ITER Advanced Scenarios

Karim Besseghir

EPFL2013