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Christophe Gissinger
Associate professor at Ecole Normale Superieure (ENS Paris)
DYNAMO THEORY

Dynamo is the mechanism by which magnetic fields of planets and stars are generated and amplified by the turbulent motions of the underlying electrically conducting fluid. We combine experiments, theory and numerical simulations to explore the exact mechanisms of magnetic field generation and its associated dynamics. Numerical modelling of the Earth core is a typical example of my research activities: for instance, we have studied how chaotic reversals of the Earth magnetic field can be generated in geodynamo simulations when the equatorial symmetry of the flow is broken by a heterogeneous heating at the core-mantle boundary. On the other side, experimental approach is very useful: I participated to the VKS experiment, the first experiment which reproduced dynamo field generation in a fully turbulent flow. In this experiment, we were able to reproduce field polarity reversals, which finally lead us to propose new models for the dynamics of astrophysical dynamos.

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vks simuls
lvks experiment
vks simuls
ELECTROMAGNETICALLY DRIVEN FLOWS

Plasmas and liquid metal can be put in motion by Lorentz forces, rather than driven by pressure gradients or mechanical impellers. This new situation can lead to very complex behaviors and fundamental questions. It is well known that a time varying magnetic field acting on an electrically conducting fluid causes motion within this fluid. Such electromagnetically induced flows are found in many applications, such as induction melting, magnetic levitation, or electromagnetic stirring. These types of induced flows also appear in nature, for instance in internal salty oceans of Jupiter’s moons. I try to study both theoretical and experimental aspects of these electromagnetically driven flows. In particular, we study the emergence of new MHD instabilities in these systems.

dipole
vks simuls
lvks experiment
CHAOS AND NON-LINEAR DYNAMICS

I also work on various non-linear problems, ranging from low-dimensional behavior in fluid dynamics to chaotic motions of mechanical systems. In general, one expects turbulent flows to show a very complex behavior, due to the infinite number of degrees of freedom. Yet, several turbulent systems, MHD or not, exhibit low-dimensional dynamics involving chaotic reversals between two symmetrical states. I work on deterministic or stochastic models aiming to understand such complex behaviors, using only a few modes in interaction.

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dipole
OTHER INTERESTS

I am also interested in other problems, ranging from astrophysical to laboratory scales. Below are some typical questions that picked my interest over the last years : is it possible to simply understand how the magnetic field of galaxies is generated ? What is the mechanism for the destabilization of accretions discs around black holes and stars? How efficient are shear layer instabilities for angular momentum transport ? I also have a strong interest for Taylor-Couette flow, in both spherical and cylindrical geometries...

lvks experiment
dipole
lvks experiment