Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session DT1: Plasma Thrusters |
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Chair: Ricky Tang, Sandia National Laboratories Room: Century I |
Tuesday, October 29, 2019 10:00AM - 10:15AM |
DT1.00001: Hall thrusters instabilities analysis with 2D (axial-azimuthal) Particle-In-Cell simulations Thomas Charoy, Antoine Tavant, Anne Bourdon, Pascal Chabert In the last decade, Hall-Effect Thrusters (HET) have been widely used for spacecraft propulsion. However, even though many studies have been conducted, the electron transport across the magnetic field is still not well understood. It has been experimentally observed by Meezan et al. that the electron mobility across the discharge chamber is higher than the one expected with the classical collisional theory. Recent studies have shown that this anomalous transport could be due to the Electron Cyclotron Drift Instabilities (ECDI). Nevertheless, many other instabilities can be observed in a HET, with a wide range of frequencies and they might also affect the discharge behavior. \\ 2D Particle-In-Cell (PIC) simulations of the axial-azimuthal plane of a HET have been performed with \textit{LPPic}, a code previously validated with a 1D Helium benchmark and a 2D ExB benchmark. Compared to the latest, here we solved the neutral gas dynamic self-consistently and hence, we were able to capture the breathing mode oscillations along with the ECDI. We studied the coupling between these two instabilities, with comparison to the theory recently developed by Lafleur et al. The influence of discharge parameters and numerical models on the discharge behavior is also shown. [Preview Abstract] |
Tuesday, October 29, 2019 10:15AM - 10:30AM |
DT1.00002: Self-organization of a turbulence-driven ionization instability in hollow cathodes Marcel Georgin, Benjamin Jorns, Alec Gallimore The self-organization of a plasma into a coherent state is a common phenomenon in nature and plasma technology and in many cases is poorly understood. In the area of low-temperature plasma devices, this is an active area of research as these self-organized states can sometimes be favorable or detrimental for their operation. For example, the hollow cathode is a widely used plasma device that, under some operating conditions, appears to exhibit an oscillatory form of self-organization, the so-called "plume mode" instability. This instability is commonly found in cathodes designed for plasma propulsion devices and occurs at low flow-rate. Historically thought to be ionization wave, this structure is characterized by large-scale, low-frequency oscillations in potential and density. Classical descriptions of this instability do not predict its onset; however, cathode plasmas are notably dominated by the non-classical effects of small-scale electrostatic turbulence. Recent numerical and experimental work has correlated these density oscillations with fluctuations in the turbulence. In this work, we examine the variations in turbulence and their correlation with the ionization rate. To interpret our result, we develop a zero-dimensional model for this turbulence-driven instability. [Preview Abstract] |
(Author Not Attending)
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DT1.00003: Iodine RF-ICP for Electric Propulsion: Global Model and Experimental Comparisons Florian Marmuse, Cyril Drag, Anne Bourdon, Jean-Paul Booth, Romain Lucken, Pietro Congedo, Nicolas Sisourat, Olivier Le Maitre, Pascal Chabert Iodine can be a replacement for Xenon as propellant for electric propulsion devices, being cheaper and allowing denser storage without pressurized system. Despite such thrusters being available on the market, the community lacks a better understanding of iodine Inductively Coupled Plasmas (ICP) and better methods to diagnostic them. Here we present an updated version of a global model for plasma ICPs, deriving temperatures and densities of six species linked by 16 reactions, and the plasma impedance, as well as thruster performances if the ICP is connected to a set of biased grids. An uncertainty quantification strategy has been applied to present a model with absolute uncertainties as well as indications of the sources of those uncertainties. We also present several experimental techniques applied to measure key plasma parameters: Langmuir probe measurements for electron density and temperature, I absorption at 1315nm for I density and temperature, I2 absorption for I2 density to compare with pressure measurements, and emission spectroscopy. As an example, the recombination effect is shown to be much stronger than anticipated by models and some hypothesis are made to explain this, leading to new constraints on the value of the I2 recombination coefficient at the walls. [Preview Abstract] |
Tuesday, October 29, 2019 10:45AM - 11:00AM |
DT1.00004: Predicting secondary electron emission rate in Hall Effect Thrusters Antoine Tavant, Romain Lucken, Anne Bourdon, Pascal Chabert In Hall Effect Thrusters (HET), the dielectric material used for the lateral walls is observed to have an impact on the discharge behavior and thruster performances. Recent particle in cell (PIC) simulations have shown that the electron cross-field transport in HET comes chiefly from both the azimuthal instability and the electron-wall collisions and not from the secondary electron emission (SEE) induced by electron impact on the lateral walls. On the other hand, an increase of the SEE yield can reduce the sheath potential drop at the wall, and hence increases the electron power losses. Using a two-dimensional PIC simulation of the radial-azimuthal plane at the exit plane of a HET, we have carried out a parametric study over the parameters of SEE at the wall. From the simulation results, we have derived a polytropic state law that allows us to close the fluid equations for the electrons with a non-Maxwellian energy distribution function. This model allows to link the electron temperature at the center of the discharge with the temperature at the wall and then to model more accurately the effects of the wall material in HET in low dimensional simulations, hence reducing the time and cost of HET development. [Preview Abstract] |
Tuesday, October 29, 2019 11:00AM - 11:15AM |
DT1.00005: Hybrid modeling of the anomalous transport inside Hall thrusters Alejandro Alvarez Laguna, Marc Massot, Pascal Chabert, Anne Bourdon We present a hybrid strategy that combines the fluid and the kinetic descriptions for the simulation of Hall thrusters. The objective of the model is to selfconsistently capture, in an efficient manner, the important kinetic effects that are responsible for the anomalous transport of electrons across the magnetic field and the plasmawall interaction. The fluid model simulates the evolution of the macroscopic quantities. A novel numerical scheme will be presented in this work. The fluid description is computationally more efficient than the kinetic model. However, it fails to capture the anomalous transport. In PIC simulations, the distribution function of the electrons is observed to deviate from the Maxwellian distribution, which appears to have an important impact on the development of the instability. In the hybrid model, a MonteCarlo simulation is carried out in order to estimate the distribution functions of the species. The numerical algorithm can be applied to different low-temperature plasmas under low-pressure conditions applications. [Preview Abstract] |
Tuesday, October 29, 2019 11:15AM - 11:30AM |
DT1.00006: Genesis of non- uniformity of plasma fluxes over emissive wall in low-temperature plasmas Irina Schweigert, Mitchell Walker, Michael Keidar A spatial non-uniformity of electron and ion fluxes on the treated surfaces in plasma devices can be provoked by various factors, for example, a non-planar topology, difference in the electron emission yield of materials in segmented surface or the presence of an oblique external magnetic field. In these cases, a feedback between plasma fluxes and surface structure (through the non-planar surface sheath) can lead to an essential modification of the surface during plasma device operation. In PIC MCC simulations and in the experiment, the plasma sheath transition near the grooved emissive surface, segmented emissive surface stimulated by an increase of the energy of electron is studied. It is shown that the modulation electron and ion fluxes to the surface increases after the transition. The effect of external oblique magnetic field on plasma structure is studied in PIC MCC simulations. The formation of periodical plasma structure and effect of variation of electron energy and magnetic field strength on this structure is discussed. It is shown that enlarging the inclination of the magnetic field leads to increasing non-uniformity of ion and electron fluxes on the wall. [Preview Abstract] |
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