Electron dynamics and the mode-transition of a non-neutral discharge regime of the COST jet

In contrast to low-pressure plasmas, where the Debye length λ_D and the discharge length L differ by several orders of magnitude, many atmospheric pressure plasmas inherit comparable scales for these quantities. As a result of this characteristic, atmospheric pressure plasmas can fail to develop a quasi-neutral bulk region and operate in a non-neutral discharge regime. In previous work, we have shown that the electrons in this regime become organized in a soliton-like structure. Moreover, this Gaussian-shaped group of electrons organizes according to its center of mass (COM). This COM is in Boltzmann equilibrium, and its dynamics determine the electron dynamics as a whole. An unanswered question arising from analyzing the non-neutral regime is about its mode transitions and boundaries. The main goal of this work is to answer this question. We apply a one-dimensional hybrid particle-in-cell/Monte Carlo collisions (PIC/MCC) simulation simulating the electrode gap of the COST jet's cross-section. The influence of varied parameters (e.g., the applied voltage or the driving frequency) on the non-neutrality of the discharge is reported. Furthermore, this work pays special attention to the influence of the parameter-variation and mode transition on the electron dynamics.