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Home > About us > Media > Archived news > 2016 > Ecole Polytechnique Thesis Award for Nicolas Dorville, a former LPP PhD student
Ecole Polytechnique Thesis Award for Nicolas Dorville, a former LPP PhD student
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The terrestrial magnetopause is the boundary between the solar wind (compressed by a shock) and the terrestrial magnetosphere. This kind of thin and nearly impenetrable boundary naturally forms each time two magnetized plasmas are pushed one toward another. It happens here, like for several astrophysical situations, in a collisionless medium. For these reasons, the terrestrial magnetopause, accessible experimentally with a lot of satellite missions, is representative of a very general type of interfaces. Key phenomena like plasma transport across the boundary, heating and acceleration of charged particles or magnetic reconnection, take place at these interfaces. Therefore, studying and deeply understanding such kind of boundary is critical to understand fundamental plasma physics.
The terrestrial magnetopause is the boundary between two plasmas of different densities and temperatures. The magnetic fields of the magnetosphere and the solar wind have also different directions and intensities. The transition observed at the magnetopause therefore concerns matter, with two interpenetrating plasmas, and fields. How do these different kinds of variations combine and what structure does it give to the boundary? These are the questions that have been studied in this work. The simplest case, when the boundary can be considered locally as a plane and stationary, will be the basis of the study, but the thesis also shows how a boundary shaken by instabilities and magnetic reconnection can deviate from these simple models.
The first part of Nicolas Dorville’s thesis consists in an experimental study of the magnetopause using data from the European Cluster mission. It shows how to combine magnetic and ion data to obtain a characterization of the normal direction to the boundary and a coordinate along this normal. Then, he shows that, when the normal magnetic field is nonzero, the boundary can be a succession of small layers bearing separately the rotational and compressional variations.
In the second part of the thesis, a theoretical model of the structure is developed, as a 1D-stationay equilibrium of a current layer, like the magnetopause. This equilibrium is a kinetic one, which means that it is valid for the distribution function, and not only its first moments like density, fluid velocity, and pressure. This is necessary in a collisionless medium as soon as the characteristic scale of the particle motion, particularly the Larmor radius, is not negligible with respect to the thickness of the layer. Such kinds of equilibria are particularly necessary for initializing the numerical simulations that are used to study the magnetopause and the instabilities that can happen at the boundary, like the tearing instability (which implies reconnection).
References:
– Thèse: http://www.theses.fr/2015EPXX0015
– Dorville N., Belmont G., Rezeau L., Grappin R., Retinò A., Rotational/compressional nature of the magnetopause : Application of the BV technique on a magnetopause case study, Journal of Geophysical Research Space Physics 119 1898-1908 (2014)
– Dorville, N., G. Belmont, L. Rezeau, N. Aunai, and A. Retinò (2014), BV technique for investigating 1-D interfaces, J. Geophys. Res. Space Physics, 119, 1709–1720, doi:10.1002/2013JA018926.
– Dorville, N., Belmont, G., Aunai, N., Dargent, J., Rezeau, L., Asymmetric kinetic equilibria: Generalization of the BAS model for rotating magnetic profile and non-zero electric field, Physics of Plasmas, 22, 092904 (2015); doi: 10.1063/1.4930210
Also in this section :
- A new book by Sébastien Galtier: Introduction to Modern Magnetohydrodynamics
- Two clean rooms for its space experiments in the premises of LPP at UPMC, Jussieu Paris
- Happy New Year 2016 from LPP
- Air Serenity, LPP spin-off, back from Consumer Electronics Show (CES) in Las Vegas
- Collaboration between LPP and the University of Nevada, Reno (UNR): new configuration of Z-pinches for Inertial Confinement Fusion and the first realization of a civil current-driven indirect heating cavity, called hohlraum
- The next symposium of the French Solar - Terrestrial National Program (PNST) will be held from March 14 to March 16 in Hendaye, France.
- The ANR ValCO2Plas kick off meeting took place on March 15 at LPP
- Shiyong Huang received an Outstanding Young Scientist award during the European Geophysical Union (EGU) general assembly, on April 20th, in Vienna
- Summer school in Corsica: advances in geophysical and astrophysical turbulence
- Signature of a convention between Ecole Polytechnique and SATT Paris-Saclay to support the project MINIATURE
- A special issue of GRL journal for MMS mission first results
- Confirmation of Cluster mission extension in 2017 and 2018
- SYCAMORE project Kick off : how to recycle CO2 in a clean and useful way
