Particle-in-cell simulations of planar and cylindrical Langmuir probes: Floating potential and ion saturation current

Particle-in-cell and hybrid electron-Boltzmann simulations of planar and cylindrical Langmuir probes are compared with various probe theories. Floating potentials for planar and cylindrical probes are calculated and significant deviations from the typical approximation used for argon discharges of similar to 5T(e) are shown. The interpretation of simulated ion saturation currents by the orbital motion limited and the Laframboise theories result in an overestimation of the ion density. On the other hand, the cold-ion theory underestimates the ion density. These deviations are related to the overestimation and underestimation, respectively, of the ion orbital motion around cylindrical probes. The best agreement is obtained when the probe theory suggested by Tichy et al. is used. This theory incorporates ion orbital motion as in the Laframboise theory, collisional orbital motion destruction as suggested by Zakrzewski and Kopiczynski, and ion scattering as given by Chouet al. (c) 2006 American Vacuum Society.