Link do spotkania w aplikacji Microsoft Teams: https://tiny.pl/j6jw7_g5

Abstract

Hall thruster plasma discharges are subjected to a variety of plasma oscillations. The oscillation spectrum spans across a wide 10 kHz-MHz range with low-frequency discharge current oscillations, commonly referred to as the breathing mode, being of the most prominent oscillatory modes. Although the exact physical mechanism is still being studied, the nature of the breathing mode as an ionization instability has been firmly established. A predator-prey interpretation has gained canonical status due to its simplicity and generally provides a phenomenologically truthful picture of the instability as alternating periods of rapid ionization and slow propellant replenishment.

Breathing mode oscillations are generally thought to be detrimental Hall thruster performance, so that extensive research efforts have been undertaken to determine operational regimes with minimized oscillatory behavior. Despite immense practical importance of such parametric studies, which translate to helpful engineering instructions, they provide limited insights into the exact physics of the breathing mode and fail to converge at one final conclusion on conditions leading to breathing mode onset. The real question here is whether it is possible to pin down a condition – a breathing mode trigger – which leads to breathing mode emergence? In other words, what features must a Hall thruster plasma discharge exhibit to develop the breathing mode instability?

In this talk, we employ a former breathing mode theory to try to answer this question. The theory is based our two steady-state functions γ(x) and Ψ(x), which can be extracted from conventional numerical simulations. The main claim of the theory is that functions γ(x) and Ψ(x) are proficient in recovering the most relevant aspects of a Hall discharge from perspective of the breathing mode instability. Within the theory, operational parameters of a Hall thruster effectively act only as control parameters on the γ(x) and Ψ(x) profiles exhibited by a given discharge. It is ultimately the γ(x) and Ψ(x) distributions within the discharge channel which determine whether oscillations emerge – part of this study is to determine which γ(x) and Ψ(x) distributions are susceptible to breathing mode oscillations and which γ(x) and Ψ(x) distributions are not. Moreover, an intriguing relation of the Ψ(x) function to the point of zero ion velocity is found. The point of zero ion velocity turns out to be a reliable point of reference for global discharge dynamics.