Kinetic modeling of an atmospheric pressure argon plasma in contact with a floating collector

Abstract

Summary form only given, as follows. The problem of an atmospheric pressure argon plasma in contact with a floating collector is considered through the framework of the kinetic Boltzmann equation. A BGK collision term where only weak deviations from the Maxwellian velocity distribution are allowed is considered for the electron equation. This collision term for the ion is more comprehensive and accounts for large potential deviations from the Maxwellian distribution. Due to the relatively low mean energies expected, only the momentum transfer collisions are considered. The normalized Boltzmann equations are solved self-consistently with Poisson's equation using the method of fractional steps with cubic spline interpolation. The results show that the sheath region extends about 25 Debye lengths from the floating collector surface and that the sheath voltage drop is /spl sim/6.5 V. The electron current density peaks at a distance of /spl sim/9 Debye lengths while the ion current remains essentially constant from the plasma edge to the collector up to a distance of /spl sim/9 Debye lengths, and then sharply drops to zero at the collector surface. Both currents at the collector are similar in magnitude giving rise to a zero collection current. The electron velocity distribution remains very close to a Maxwellian throughout the x-space while the ion distribution shows a smooth transition from a Maxwellian at the plasma edge to a distribution showing strong ion accelerations towards negative velocities near the collector surface. Further work is in progress to extend the kinetic model to include a thermionic electron beam and aims at a kinetic description of the cathode region of high-pressure arc discharges.