The thesis will be carried out within the framework of A*MIDEX funding and a collabo-
ration between the PIIM, the Laboratoire de Physique at Ecole Normale Supérieure de Lyon
(LPENSL) and also the Laplace laboratories for the theoretical part.

The thesis will take place mainly at PIIM in Marseille although the future student will have to travel regularly to Lyon to the LPENSL.

By nature, a plasma is composed of charged particles which, in response to electromagnetic
fields they generate or which are applied to them, exhibit collective behaviors from which quasi-
neutrality results on spatial scales larger than the Debye length. This property break-down
when the plasma encounters a solid frontiers where non-neutral sheath forms at scales of a few
Debye lengths and, potentially, deeply impact on the bulk dynamics, i.e. far from the frontiers.

The physics of plasma sheath is of major interest in the fields of, both, laboratory, astrophysics and fusion by magnetic confinement (tokamaks,…). Many studies have been devoted to the understanding of plasma sheaths in several configurations. The situation is further complicated in the presence of magnetic fields or the emission of electrons from the surface. In the presence of surfaces that emit electrons, either from secondary emission or thermionic emission, the physics of the sheath is deeply modified. Modeling and numerical simulations predict an « inverse sheath » whose experimental observation is still elusive.

In that context, the long-term goal of the thesis is to improve comparison between magnetic
sheath of an electrons emitted surface models and experiments. Models and experiments will
be performed and compared at the laboratory PIIM and its partners by two PhD students.

Various experiments will be performed and compared to theories developed within a distinct
PhD project, by a fellow PhD student funded by the same research grant:
• Explore the collisionality of the sheath physics, which are ubiquitous in nature and ex-
periments, by changing the neutral pressure
• Measurements of the sheath structure of an thermionic, electron emissive surface (heated Tungsten)
• Measurements of the sheath structure in the case ofs urfaces with highs econdary electrons
emission rates, with a focus on the observation of an « inverse » sheath structure.
• Explore the effect of magnetic fields on the sheath structure, in regimes where only the
electrons will be magnetised. The influence of the the angle between the surface and the
magnetic field is known to be a key player .
• Perform experiments in a linear magnetic plasma column