Plasma sheaths in Hall discharge

The sheath region of a Hall discharge is studied in a four-dimensional phase space which consists of one spatial (radial in cylindrical metrics) and three velocity dimensions by means of a particle-in-cell/Monte Carlo model coupled with a probabilistic method for the secondary electron emission. Different axial regions (anode, ionization, and acceleration zones) of the channel have been investigated using the local field approximation and distinguishing between inner and outer walls. The presheath and sheath structures are different in the three regions simulated showing a charge saturated regime in the acceleration region. Small differences in behavior for the external and internal walls of the channel are detected. Further, trapped ions are found near the walls in the acceleration region which could have an important effect on the wall recombination enhancing the axial electron current. The results could be used to obtain boundary conditions and lateral wall losses which are suitable for incorporation into one-axial and two-dimensional macroscopic models which simulate the bulk neutral plasma in Hall discharge.