Kinetic study of magnetized plasma-wall interaction

In fusion devices, the region of plasma directly in contact with a material surface (limiter, divertor) can erode the surface and release impurities, which migrate toward the bulk plasma and deteriorate its confinement. In this thesis, we studied the plasma-wall interaction using a Vlasov-Poisson model. This kinetic model allowed us to investigate the three different regions (Debye sheath, magnetic and collisional pre-sheaths) that compose the transition between a low-pressure plasma and a wall when a tilted magnetic field is present. Particular attention was devoted to the physical properties of ions entering the Debye sheath and the role of ion-neutral collisions on the Bohm criterion. Moreover, we showed that, in the presence of a tilted magnetic field, the ion distribution function is significantly distorted from its Maxwellian shape in the bulk plasma, thus requiring a fully kinetic study. Using the computed ion distributions on the wall, we estimated the wall sputtering rate in terms of the magnetic field strength and angle of incidence. We showed in particular that, for grazing incidence, the sputtering rate is reduced because of two effects: first, the ion flux is spread over a larger area and, second, the grazing magnetic field limits the kinetic energy of ion population. As plasmas are generally composed of more than one species, we extended our model to simulate an argon-helium plasma. Our study focused on the Bohm criterion at the Debye sheath entrance and its modifications brought by the introduction of a second ion species. (author)