Numerically simulated influence of positive ions on the propagation of a positive streamer initiated in an argon plasma jet

Abstract

A plasma jet with inert working gas operates in a streamer discharge mechanism. The propagation behavior of streamers determines the distribution of active species, which play a key role in the applications of plasma jets. To make clear streamer behavior under the influence of residual positive ions, a two-dimensional fluid model based on the continuity, the conservation, and Poisson's equations is employed to numerically investigate the dynamic behavior of a positive streamer when it approaches a cloud of positive ions with different densities and scales. Results indicate that the streamer always propagates along the axis and passes through the cloud of positive ions if the ions are rarefied (1.0 × 1016 m−3 in the core), which behaves like a free streamer. If the ion cloud has a medium density (5.0 × 1016 m−3 in the core), the streamer first deflects upward when it approaches the vicinity of the ion cloud and then deflects downward when it departs from the ion cloud, leaving a detouring track. The detouring track is also left if the ions are fairly dense (1.0 × 1017 m−3 in the core). However, the detouring process is fulfilled by the relay of two streamers, which are initiated at the jet nozzle and inside the ion cloud, respectively. Moreover, the velocity of the streamer is simulated with varying ion densities, voltage amplitudes, and gap widths. In addition, the deflection amplitude of the detouring track is investigated as a function of the voltage amplitude, gap width, ion density, cloud position, and cloud scale.