Missions

Carbon-free power production using magnetic confinement fusion is an ambitious scientific and technological endeavor requiring a sustained research effort. Among the challenges on the path to fusion reactors, the management of heat exhaust is one of the most critical ones. The strategy to manage the extreme heat fluxes to the reactor wall relies on the dissipation of the plasma's energy through interaction with the neutral gas present in the edge of the plasma due to plasma-surface interaction. The physics at play consists in a balance between plasma transport, dominated by turbulence, and atomic and molecular reactions related to plasma-neutrals collisions. The modelling of this extremely non-linear phenomenology is mandatory for the design and operational space definition of future devices like ITER.
A central aspect for the modelling of this issue is the development of a boundary layer, the sheath, at the contact point between the plasma and the solid surfaces. The sheath has a major impact on the trajectory of particles in the vicinity of the solid surface and both determines the boundary conditions for the plasma out-flux to the wall and the conditions of emission of neutral particles emitted after interaction with the solid. Past studies have showed that refining the description of the sheath can have a significant impact on plasma conditions and eventually heat exhaust.
The proposed Postdoc is part of a project funded by the French National Research Agency aiming at achieving self-consistent modelling of heat exhaust issues in magnetic confinement devices by developing and exploiting for the first time a code able to describe self-consistently edge plasma turbulence, plasma-wall interactions and neutrals dynamics. In order to achieve this, the project brings to together complementary expertise from different laboratories belonging to two related scientific communities: the fusion plasma community (IRFM/CEA Cadarache) and the low-temperature plasma community working on applications such as Hall thrusters which are also governed by sheath physics, plasma-neutrals interactions and turbulence (LAPLACE Toulouse).

Activités

The objective of the Postdoc project is to improve key aspects of current models by combining the modeling methods and knowledge existing in these two communities. The project will thus be led in close collaboration between the teams of the LAPLACE laboratory and those of IRFM. The focus is on the physics of the plasma sheath in conditions relevant to the divertor of large scale fusion devices, especially the link between plasma conditions at the magnetic pre-sheath entrance (used as boundary conditions for fluid models) and the distribution function of ions in angle and energy at the wall. Experimental evidence from tile topography in Tore Supra (the Tokamak in CEA Cadarache, now named WEST) showed that a guiding center approximation misses important features of this distribution. It turns out that finite ion Larmor radius effects must be taken into consideration for the calculation of the ion incidence angle while impacting the divertor surface (the magnetic field lines are at grazing incidence). This affects consequently the reemission angle of neutrals off the wall and has implications on the plasma-neutral interaction and hence on the overall properties of detached plasmas. Particle drifts will be assessed in detail and in particular the changes induced by a reversal of the magnetic field direction. This task will be both of theoretical and numerical nature. The candidate will use and modify a 1D/2D-3V parallelized explicit Particle-In-Cell algorithm developed in house (written in Fortan 90). The obtained results will be used both to improve the description of the re-emission of neutral particles at the wall as well as to propose recommendations for the description of plasma boundary conditions at the sheath entrance.

Compétences

Applicants should have: (1) a PhD thesis in physics; (2) good knowledge of plasma physics, statistical physics and/or fluid dynamics; (3) a keen interest in theory and numerical simulation. Before the contract can start, a security check procedure of several months will be necessary.

Contexte de travail

This position is funded by the ANR PLATUN project (Interaction between Turbulence and Neutral Dynamics in Tokamak Onboard Plasma) which started in 2022, with the following a consortium: IRFM/CEA Cadarache, Aix-Marseille University, IJL Nancy and LAPLACE Toulouse.
LAPLACE (Laboratory for Plasmas and Energy Conversion) is a joint research unit of CNRS, INP-Toulouse and the University of Toulouse. This laboratory has a staff of over 300 and represents the largest concentration of research in electrical engineering and low-temperature plasmas in France. The work will take place on the LAPLACE premises on the University of Toulouse III campus, within the GREPHE team (Energetics, Plasmas and Non-Equilibrium dynamics) known e.g. for its work on magnetized plasmas for space propulsion. The work will be supervised by Gwenael Fubiani and Gerjan Hagelaar of LAPLACE and Patrick Tamain of IRFM/CEA.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.