  Radio-frequency-driven atmospheric pressure plasma jets (RF APPJs) play an
essential role in many technological applications. This work studies the
characteristics of these discharges in the so-called non-neutral regime where
the conventional structure of a quasi-neutral bulk and an electron depleted
sheath does not develop, and the electrons are instead organized in a
drift-soliton-like structure that never reaches quasi-neutrality. A hybrid
particle-in-cell/Monte Carlo collisions (PIC/MCC) simulation is set up, which
combines a fully kinetic electron model via the PIC/MCC algorithm with a
drift-diffusion model for the ions. In addition, an analytical model for the
electron dynamics is formulated. The formation of the soliton-like structure
and the connection between the soliton and the electron dynamics are
investigated. The location of the electron group follows a drift equation,
while the spatial shape can be described by Poisson-Boltzmann equilibrium in a
co-moving frame. A stability analysis is conducted using the Lyapunov method
and a linear stability analysis. A comparison of the numerical simulation with
the analytical models yields a good agreement.

Plasma Physics