Kinetic-theory-based investigation of electronegative plasma–wall transition with two populations of electrons

Kinetic theory has been employed to investigate the magnetized plasma-sheath structure and its
characteristics in the presence of more than one species of negatively charged particles: hot electrons,
cold electrons, and negative ions. The cold electrons and negative ions are considered to obey a
Maxwellian distribution, whereas the hot electrons follow a truncated Maxwellian distribution. The
Bohm sheath condition has been extended for the case of more than one species of negatively
charged particles, in which the concentration of hot electrons has a crucial role in achieving the
Bohm velocity. The thermal motion of hot electrons is much higher compared to cold electrons and
negative ions, such that the variation of hot electron concentrations and the temperature ratio of hot to
cold electrons play a key role in the determination of the plasma-sheath parameters: particle densities,
electrostatic potential, the flow of positive ions towards the wall, and sheath thickness. We have
estimated the deviation of the resultant drift velocity of positive ions on the plane perpendicular to the
wall from the parallel component at the presheath–sheath interface. It is found that the deviation
between the two velocity components increases with an increase in the obliqueness of the magnetic
field. Furthermore, the results obtained from the kinetic trajectory simulation model are compared
with the results obtained using a fluid model; the results are qualitatively similar, although the
potential varies by less than 4% in terms of the magnitude at the wall.