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Ludovic Petitdemange                                                                                                               FRENCH VERSION  
CNRS researcher at Paris Observatory

cest ma photo      Observatoire de Paris (LERMA)  
      61 avenue de l'Observatoire  
     75014 Paris, France  

    Contact :
      Office :             D18=L269c
      Phone :             +33 (0)1 44 32 25 80
      E-Mail :            ludovic.petitdemange at


 Research interest

I am a CNRS researcher interested in understanding dynamo action occuring in astrophysical objects (stars and planets). I work at ENS-Paris in the LRA Laboratory which corresponds to LERMA Laboratory located at ENS. I performed my PhD thesis in Astrophysics (ED127) at the LRA, Ecole Normale Supérieure (Paris) in 2009 under the supervision of Emmanuel Dormy and Steven Balbus on "MagnetoRotational Instability and Planetary Interiors"

My research focus on magnetohydrodynamics and, in particular, on numerical simulations related to MHD instabilities. I am interested in modelling the dynamics and generation mechanisms of natural dynamos. I do my best to understand the physical mechanisms which affect the magnitude, the topology and the time variations of stellar and planetary magnetic fields.

MagnetoRotational Instability
The MagnetoRotational Instability (MRI) is a fluid instability arising in MHD flows when the angular velocity decreases outward and a magnetic field is applied. It is currently the best candidate to explain angular momentum transport in accretion disks around stars and black holes. Indeed, the MRI explains how a weak magnetic field can destabilize otherwise stable Keplerian flows. Despite its simplicity, several theoretical aspects of this instability are still poorly known, like the mechanisms of saturation of the MRI, the emergence of non-axisymmetric modes or the interaction with dynamo fields.

Dynamo problem
It is strongly believed that magnetism of planets, stars and galaxies is due to the self generation of a magnetic field by the turbulent motion of an electrically conducting fluid. However, a lot of questions remain unsolved: what are exactly the mechanisms of the field generation? What determines the complex dynamics of the field, like periodic oscillations or chaotic reversals? What is the role of  turbulence or how saturation of the field occurs ?

Numerical modelling

A lot of characteristics of dynamo or MRI experiments remain not fully explained, and it can be very useful to use the numerical approach to understand what happens in these experiments. In this perspective, I use numerical simulations in different geometries to model dynamo action or MHD Couette flow in laboratory. Moreover, this is a unique opportunity to test directly the validity of numerical models against experimental data.

See more about my research ....           Download my Ph.D. Thesis (pdf)