Transport Coefficients of Decaying Ion Swarms in Ar Gas

Abstract This study presents predictions for the low-energy cross-section set and analyses the kinetics of molecular hydrogen ions in argon, which represents a crucial step toward reliable modelling of various technologically significant processes. Although ions can be detected in such plasmas, the conditions in an idealized, isolated system, where only their interaction with argon atoms is considered, differ significantly. Under these conditions, ions undergo rapid destruction, leading to a disruption of the hydrodynamic regime of the charged-particle ensemble. To accurately determine the kinetic properties in this non-hydrodynamic regime, a Monte Carlo simulation method is employed. As functions of weak and moderate reduced electric fields, the following kinetic quantities are provided: bulk and flux velocities, half-life, mean free path, diffusion coefficients and reaction rate coefficients. It is shown that, due to rapid ion loss through reactive collisions, the transport characteristics evolve toward well-defined asymptotic limits without establishing steady-state conditions during the swarm lifetime.