Kinetic treatment of ions in the magnetic presheath*

The magnetic presheath is a quasineutral boundary layer, extending a few typical ion Larmor radii from the wall, in which ions may intersect the wall during a gyro-orbit [1]. It is present if the magnetic field makes an oblique angle with the wall. Due to the large size and distortion of the ion gyro-orbits, a kinetic treatment is necessary to obtain the electrostatic potential across the magnetic presheath.

When the angle between magnetic field and wall is small, the ion distribution function is approximately constant when expressed in terms of appropriate quantities [2]. Hence, the ion density can be obtained [3]. The electron density is assumed to be a Boltzmann distribution. Using an iteration scheme to solve the quasineutrality equation gives the electrostatic potential across the magnetic presheath [4]. The ion distribution function entering the Debye sheath is obtained, and the dependence on ion temperature and angle is studied.

References:
[1] Chodura, Phys. Fluids 25, 1628 (1982)
[3] Cohen and Ryutov, Phys. Plasmas 5, 808 (1998)
[4] Geraldini, Parra and Militello, Plasma Phys. Control. Fusion 59, 025015 (2017)
[5] Geraldini, Parra and Militello, arXiv:1805.02975 (2018)