The plasma-wall transition (PWT) layer in a magnetic field parallel to the wall is investigated with a two-fluid approach, where the continuity and momentum equations for electrons and ions are used to describe the semi-bounded plasma, whereas the background gas of neutral particles is assumed to be uniformly distributed. The equations include ionization, recombination and charge exchange processes. The magnetic field is parallel to the confining wall, which is assumed to have a potential different from the one in the bulk plasma. A linear analysis of the PWT layer reveals two distinct length scales, namely the short Debye screening length scale and the much longer collisional length modified by the magnetic field. It is found that the ionization and recombination processes are important to connect the PWT layer to the bulk plasma, which is characterized by a balance between ionization and recombination. The PWT layer is here treated as a unit, without a priori splitting into sheath and presheath sublayers. The nonlinear set of equations is solved numerically to obtain the profiles of the electrostatic potential, the densities, and the velocity components. Near the wall, where the electron velocity is large, the Lorentz force and collisions lead to an electron density distribution significantly different from the Boltzmann one.
- plasma sheath
- magnetic field