Computational modeling of electric discharge inside electric propulsion systems by a hybrid PIC-MCC/FVM approach

本研究项目的目标是发展一种新的等离子体流动的建模概念，并将其用于电弧喷射推力器的数值研究。这种用于航天器的电力推进系统能够产生小而精确的推力，这对于卫星的姿态控制和未来卫星的预期编队飞行至关重要。从该项目中获得的知识将提高对复杂等离子体现象的理解，例如实验观察到的霍尔推进器中电子迁移率的增加，基于连续介质的电推进系统中等离子体现象建模的主要缺点之一是必须估计几个物理量，如电导率，阳极温度和传输系数。这种估计往往是基于经验的方法，这主要是由于等离子体现象的高度复杂性。此外，全动力学方法，通常避免估计的传输系数，往往表现出过高的计算要求。在本研究项目中，将采用一种基于可管理的计算要求的混合模型的方法。为此，电荷载流子建模与动力学（PIC）的方法和中性气体在等离子体中被处理为流体。流体方程的结果用于产生中性粒子云，其与动力学建模的电子相互作用。电离和重组率的动力学获得的结果的基础上确定，并纳入作为源项的中性气体的流体方程。电推进系统中等离子体现象的描述和数值模拟面临的一些挑战是在不使用经验模型的情况下确定电弧喷射推力器喷嘴中的电导率，以及为物理过程的时间和长度尺度存在很大差异的技术应用开发计算有效的方法。本研究项目的主要目标是：一个数字的调查，混合模型，使电力推进系统内的等离子体现象的准确描述。在该项目的第一阶段，该模型将开发和验证电弧喷射推进器内的电离和等离子体行为的重点。项目结束后，PIC-MCC/FVM模型可用。所开发的模型是基于电子的动力学描述，并能够在动力学水平上确定重要的等离子体和电离参数。

Goal of the present research project is the development of a new modeling concept for plasma flows and its use for the numerical study of an arcjet thruster. This type of electric propulsion system for spacecraft enables the generation of a small and precise thrust which is in turn of vital importance for the attitude control of miniaturised satellites and for the envisioned formation flight of future satellites. The knowledge gained from the project will improve the understanding of complex plasma phenomena, such as the experimentally observed increase of electron mobility in Hall thrusters.One of the main disadvantages of the continuum-based modeling of plasma phenomena in electric propulsion systems is the necessary estimation of several physical quantities such as electric conductivity, anode temperature and transport coefficients. This estimation is often based on empiric approaches, which mainly results from the high complexity of plasma phenomena. Furthermore, full kinetic approaches, which generally avoid the estimation of transport coefficients, often exhibit prohibitively high computational requirements. In the present research project, an approach based on a hybrid model with manageable computational requirements will be pursued. To this end, charge carriers are modeled with a kinetic (PIC) approach and the neutral gas in the plasma is handled as a fluid. The results of the fluid equations are used to produce a cloud of neutral particles, which interact with the kinetic modeled electrons. Ionization and recombination rates are determined based on the kinetically obtained results and are incorporated as source terms in the fluid equations for the neutral gas. Some of the challenges regarding the description and numerical modeling of plasma phenomena in electric propulsion systems are the determination of the electric conductivity in the nozzle of an arcjet thruster without using empirical models.a nd the development of computationally efficient approaches for technical applications in which large differences of time and length scales of the physical processes exist.The main goal of the present research project is the investigation of a numerical, hybrid model that allows the accurate description of the plasma phenomena inside an electric propulsion system. In the first phase of the project, the model will be developed and validated focused on the ionization and plasma behavior inside arc jet thrusters. After conclusion of the project, a PIC-MCC/FVM-Model is available. The developed model is based on a kinetic description of electrons and enables the determination of important plasma and ionization parameters at a kinetic level.