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Theoretical and experimental study of chaos and complexity in wave propagation induced by the twisting of the magnetic field lines in a laboratory stellarator.

par Elodie PICO - publié le

Thesis advisor : Thiéry PIERRE, Directeur de Recherche au CNRS
Email and address : thiery.pierre.cnrs7345

Subject description :

Waves in magnetized plasmas exhibit many propagation modes determined by the hot dielectric tensor. The radiation of a point-source antenna is most often localized on caustic surfaces, for instance resonance cones, due to the anisotropy induced by the magnetic field, by the temperature of the particles, and by the density gradient.
An experimental approach to studying wave complexity in plasmas requires a stable plasma submitted to a magnetic field. This is obtained when the magnetic field lines exhibit a torsion that cancels the unstable drift of the particles. This can be simply done by imposing a twist to the solenoidal structure containing the plasma : the stellarator configuration, introduced by Lyman Spitzer in 1950 has proved to be a very efficient confinement method.
A laboratory stellarator (STELLAR-321) is currently under study in PIIM-Institute in Marseille. The plasma is most often stable, which is quite new in a laboratory magnetized plasma. We propose, after a theoretical topological analysis of the system, to analyze the propagation of electrostatic waves on the lower hybrid branch. The waves are excited by a point-source antenna or by a loop antenna. The waves are guided along the plasma and are in fact Gould-Trivelpiece modes. The proposed PhD project consists in analysing theoretically the global modes present in this closed system in conjunction with the twisting of the magnetic field lines. The occurrence of wave chaos will be investigated. A critical component will be to include the effect of the internal feedback existing in this system.
Experimental measurements using UHF excitation/detection will be conducted in order to compare with the theoretical predictions. The link with other physical systems exhibiting a special topological phase (Berry’s phase) will be studied, that is connected with the fundamental issue of parallel transport.