The aim of this conference is to bring together mathematicians and physicists working on fields related to cosmology, which has been the subject of tremendous investigations in the past few years.

Properties of the gravitational wave background have been thoroughly explored in recent years, including their generation, propagation and detection. Progress has also been made in a unified description of weak and strong gravitational lensing, as well as in numerical and analytical analysis of the large scale structure of the universe. New properties of inflationary and de Sitter spacetimes have been uncovered, both at the classical and quantum level. In contrast, for alternative theories of gravitation with good ultraviolet behaviour, such as string theory, de Sitter-type solutions cannot emerge, and we now have a more rigorous understanding why this happens. Significant results have been reached in the design of valid quintessence scenarios using the dynamical systems approach to differential equations.

On the mathematical side, successes have been achieved toward understanding the nature of the big bang singularity and the behaviour of general solutions in its vicinity. The stability of FLRW solutions has also been the subject of various studies.

The conference will take place in Ecole Polytechnique, Palaiseau, from September 25th to September 27th.

Registration is free but mandatory. Some fundings may be available for graduate students. For this, don't hesitate to write at cosmology@sciencesconf.org

Un événement CNRS grand public intitulé « Recherche vers le futur, cap sur 2074 » se déroulera sur le campus CNRS de Gif-sur-Yvette, les samedi 29 et dimanche 30 juin, après-midis.

 Tahar Amari  interviendra sur la conférence intitulée « Tempêtes solaires : quels impacts sur la société ? ».

Plus d'informations : ici

The defense of Guillaume Bossard's habilitation on the subject: "The low energy effective action in superstring theory" will take place on Thursday, the 27th at 15:00, at CPHT in Louis Michel.

I will be followed by a “pot”.

The CPHT Young Researchers Seminar will be held on Friday 21th Juneat 3:00 PM  in Louis Michel conference room.

Mathieu Beauvillain :A Berry phase in a spinning screw.

Godefroy Meynard : Introduction to laser plasma instabilities and beam smoothing.

The seminar will be followed by a high tea.

Le séminaire des jeunes chercheurs du CPHT aura lieu le vendredi 17 mai 2024 à 15h00 à la Salle de conférence Louis Michel avec deux présentations :

Fanny Eustachon :How to quantize a prefect fluid: an effective field theory approach.

Mikel Sanchez : Large D limit of general relativity.

Le séminaire sera suivi d'un goûter.

The CPHT Young Researchers Seminar will be held on Thursday 18th April at 15h00 in Louis Michel conference room.

Tomas Mari Surkau: Deconfinement transition in QCD - A perturbative approach.

Thomas Pochart: A friendly introduction to scattering amplitudes analyticity.

The seminar will be followed by a high tea.

PhD Student

Resarch activities at CPHT: Theory of Plasmas

Thesis: Fluid and Kinetic macroscopic instabilities in a tokamak plasma
Advisors: Hinrich Lutjens

Research interests: plasma physics, MHD, gyrokinetic theory, numerical methods, simulations and modelling

Abstract:

The dynamics governing the macroscopic instabilities in a tokamak plasma depend on a wide range of space-time scales. A detailed description of the underlying physics requires an appropriate physical model. It must be more advanced than an extended fluid model, the latter being restricted to the study of MHD or bi/multi-fluid effects. Its generalization towards a totally kinetic description makes it possible to study new phenomena, such as wave-particle resonances or finite Larmor radius effects. These effects give access to new families of instabilities, prohibited in the more restricted model, or in a model with a simplified geometry.

The shape of the small section of the torus has indeed a significant influence on the resonant modes in the system. The presence of a singular magnetic surface at equilibrium, the consideration of resistive effects inside the tokamak wall or the presence of external poloidal coils that define the magnetic field at equilibrium directly influence the families of resonant modes that are allowed in the system.

The development of ever more complex models is also motivated by experimental observations, which demonstrate that a simple fluid model such as MHD does not make it possible to accurately describe the physics involved, and that it is necessary to tend towards a kinetic model. This evolution of the physical model is conditioned by the numerical method used and the HPC resources available. The purpose of it is to evolve in a state-of-the-art model from a physical and numerical point of view.

This thesis work is based on the 2-fluid/kinetic hybrid code XTOR-K developed at CPhT. In XTOR-K, the fluid dynamics of the electrons and of a given fraction of the ions of the thermalized background plasma are coupled in a self-consistent way with the dynamics of selected populations of kinetic ions, which makes it possible to address all nonlinearities of the problem. The kinetic ions are handled by a PIC 6D method, integrating exactly the trajectories along the cyclotron gyrations. Unfortunately, the latter method is very costly in computational resources. Thus, one of the goals of this thesis is to try and implement a gyrokinetic solver that would compete with the current kinetic one. Since a gyrokinetic model neglects any finite Larmor radius effect, such a solver would make it possible to significantly reduce the computational time needed for each simulation.

The current version of our XTOR-K code assumes that the boundary of the simulation domain is a perfectly conducting toroidal shell. However, a large number of instabilities are located close to this shell, and their dynamics is significantly impacted by this proximity. In order to free ourselves from this constraint, we have to continue our development effort allowing us to adopt more realistic boundary conditions, with ultimately a resistive shell and a set of poloidal magnetic coils allowing the control in time of the shape of the small plasma section as well as its vertical stability.

Marc Henneaux donnera son cours au Collège de France  sur le "Formalisme des antichamps, cohomologie BRST et renormalisation des théories de jauge" les mercredis 15, 22, 29 mai et 5, 12, 19 juin 2024.

Plus d'informations : ici

Le cours sera suivi d'un colloque les 20 et 21 juin intégré dans l'Institut d'été de l'ENS.