Abstract Details
Abstracts
Author: Alessandro Geraldini
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 15:30:23
Co-authors: F. I. Parra, F. Militello
Contact Info:
University of Maryland, College Park
1412 Chapin Street NW Apt. 403
Washington, DC 20009
USA
Abstract Text:
The magnetic presheath is a plasma-wall boundary layer whose thickness is comparable to the ion gyroradius. This layer arises when the magnetic field impinges on the wall making an oblique angle, so that the gyromotion of the ions is distorted by the electric field near the wall. Of particular interest is the fusion-relevant situation of a magnetic field at grazing angle with the wall. In this case, an asymptotic expansion of the ion trajectories in the small angle leads to a gyrokinetic-like model for closed ion orbits. To account for the ions lost to the wall during their last gyration, the gyrokinetic model is complemented by a treatment of open orbits. There are a small number of ions in open orbits, but these are important because the number of ions in closed orbits drops to zero at the wall. The kinetic model allows the analytical derivation of the local condition at the collisionless magnetic presheath entrance (generalizing the Chodura condition), and an efficient numerical solution of the quasineutrality equation (assuming Boltzmann electrons) in the collisionless magnetic presheath. The ion distribution function satisfies the kinetic Bohm condition at the Debye sheath entrance, and is predicted to become thinner at smaller values of the angle and at smaller electron temperature. The potential implications on main ion and impurity sputtering are discussed.
Comments:
