Stability of the magnetized plasma-wall transition layer

Abstract

Under the condition λD≪ρi≪ℓ (where λD is the Debye length, ρi is the ion gyro-radius, and ℓ is the smallest relevant collision length) and for the case of the obliquity of the magnetic field to the wall, the magnetized plasma-wall transition layer can be split into the following sub-layers: the Debye sheath (DS), the magnetic pre-sheath (MPS), and the collisional pre-sheath (CPS). Thanks to the above-mentioned condition, it is possible to investigate these sublayers independently of each other. In this paper, the kinetic theory of the stability of the MPS and the CPS is presented (for the DS, a small parameter, relevant for the development of the linear theory, is not found). The ion gas was assumed to move with a constant velocity, and the presence of such an ion beam made it necessary to modify the form of the Bohm–Chodura criterion and the behavior of the electric potential in the CPS. The instability rate was found to be proportional to the square root of the time.