Bohm's criterion for a plasma in the presence of oblique magnetic and electric fields
This paper studies Bohm's criterion for a magnetised plasma in contact with a neutralising wall, when the magnetic field is inclined with respect to the wall. The formation of a quasi-neutral magnetic presheath in front of the Langmuir sheath has been studied both numerically and analytically by considering polarisation drift terms. The sheath formation and the correlated Bohm criterion at the entrance of the magnetic presheath have been investigated for the 1D case, in which the electric field has only a component perpendicular to the wall. If the magnetic field is directly perpendicular to the wall, the magnetic presheath disappears and the purely electrostatic case is recovered. The paper presents a survey of the existing theory in the strictly 1D case including equations for the particle orbits, the constants of motion, the drift velocities and the resulting Bohm criterion. The theory is extended to incorporate an electric field component tangential to the wall. The conditions are defined under which a quasi 1D treatment of the problem is possible, leading to a characteristic modification of Bohm's criterion at the entrance of the magnetic presheath, both for a single-ion and a multi-ion plasma.
Bibliographic Reference: Report: JÜL-2973 EN (1994) 30 pp.
Availability: Available from Zentralbibliothek der Forschungszentrum Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
Record Number: 199510163 / Last updated on: 1995-02-07
Original language: en
Available languages: en