Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session FT4: Electric Propulsion ILive
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Chair: Gabe Xu, UAH |
Tuesday, October 6, 2020 8:00AM - 8:15AM Live |
FT4.00001: Oscillation analysis in Hall thrusters with 2D (axial-azimuthal) Particle-In-Cell simulations Thomas Charoy, Trevor Lafleur, Pascal Chabert, Anne Bourdon Hall Thrusters (HT) 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 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 HT, 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 HT have been performed with \textit{LPPic}, a code recently validated with 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 and the ion-transit time instabilities. We studied the coupling between these instabilities, with comparison to the theory recently developed by Lafleur et al. The influence of the vacuum permittivity scaling factor on the dischare behaviour has also been analyzed. [Preview Abstract] |
Tuesday, October 6, 2020 8:15AM - 8:30AM Live |
FT4.00002: Sheath instabilities at large secondary electron emission in Hall thrusters Pascal Chabert, Antoine Tavant, Thomas Charoy, Anne Bourdon Plasma-wall interactions are complex and often govern the overall operating regime of a plasma device. Plasmas are connected to walls through a thin boundary layer called sheath, where most of the potential and density gradients localize. The sheath physics has been extensively studied and models exist for most of the practical situations. However, several phenomenon observed in numerical simulations or in experiments remain unexplained. It has been recently found in particle-in-cell (PIC) simulations treating plasma-wall interactions in hall thrusters that the sheath may become unstable when secondary electron emission from the walls, induced by energetic primary electrons, is an important phenomenon. This presentation presents a theory of these instabilities. The theory is based on global balance equations for the electron energy and the charges in the sheath. The theory is compared to PIC simulations. [Preview Abstract] |
Tuesday, October 6, 2020 8:30AM - 8:45AM Live |
FT4.00003: Experimental and numerical investigation of an iodine plasma Florian Marmuse, Benjamin Esteves, Cyril Drag, Jean-Paul Booth, Anne Bourdone, Pascal Chabert Iodine is an alternative propellant for the electric propulsion of satellites, for which models and dedicated diagnostics are scarce. In this work, tools and processes are developed to ensure the safety of operators and experimental setups during iodine experiments. Four optical diagnostics are developed and installed on the ionization chamber of the PEGASES thruster. They lead for the first time to the density and temperature of I, and the density of I2: emission spectroscopy, laser absorption coupled to Doppler-free saturated absorption spectroscopy at 10969 and 11036, laser absorption spectroscopy at 7603cm-1, and broadband absorption spectroscopy from 480nm to 500nm. Langmuir probe measurements yield the electron density and temperature, and their spatial evolution in the plasma. Confronting this data to a global model shows that the model overestimates the molecular dissociation and the electron density. These discrepancies are shown to be partly explained by underestimated power losses phenomena in the plasma, possibly linked to its molecular and electronegative nature. This work gives leads for future theoretical work and diagnostics on I2 plasmas. It proposes an updated model and a set of new diagnostics for use to further develop iodine-based propulsion systems. [Preview Abstract] |
Tuesday, October 6, 2020 8:45AM - 9:00AM Live |
FT4.00004: The Effect of Modulation on the Magnetically Shielded Miniature (MaSMi) Hall Thruster's Performance and Plasma Properties Jacob Simmonds, Vernon Chaplin, Yevgeny Raitses Recent studies of cylindrical Hall thrusters have shown that by applying an oscillation to the anode voltage in resonance with the natural breathing modes, propellant utilization may be improved through increased plasma density in the ionization front [1]. Such an operating regime may increase performance of thrusters limited by incomplete ionization of the propellant. This approach was utilized with NASA JPL's Magnetically Shielded Miniature (MaSMi) Hall Thruster, using one-dimensional fluid/hybrid simulations from the LANDMARK project. Through semi-empirical mobility profiles, agreement between measurements -- such as axial ion velocity profiles -- was found between experiments, our 1d simulations, and 2d simulations from JPL's Hall2De code. Improvements in the propellant utilization were observed in the simulations at high amplitudes of modulation. Modulation appears to increase thrust due to the increased ion energy and ion current, however this is counteracted by increased discharge power. Large nonlinear oscillations in plasma density were observed during modulation, with similar phasing behavior between plasma parameters as in other modulated Hall thrusters. [1] Romadanov, I. et al., Plasma Sources Sci. Technol. 25, 011604 (2018) [Preview Abstract] |
Tuesday, October 6, 2020 9:00AM - 9:15AM Live |
FT4.00005: Expansion of a plasma plume with pulsed electron neutralization Lui Habl, Trevor Lafleur, Dmytro Rafalskyi, Ane Aanesland, Pascal Chabert Plasma plumes produced by gridded ion sources are generally neutralized by an external electron source which provides a continuous current that maintains quasi-neutrality in the plume and charge balance of the source. Recently, a new neutralization technique was developed, based on radio-frequency biasing of ion acceleration grids, which allows the extraction of electrons from the same plasma source as the ions, and their injection into the plume in short pulses. The effects of pulsed neutralization on the plume expansion are still not well understood, but experiments have shown the presence of a strongly anisotropic and high-temperature electron population, in contrast with common gridded ion sources. As a first approach to understand the phenomena involved in this type of neutralization, we make use of a two dimensional particle-in-cell (PIC) code to analyze the plume with pulsed neutralization. We present a comparison between the expansion from the pulsed neutralization scheme and conventional DC ambipolar expansion, before performing a detailed parametric study analyzing the influence of the pulse frequency and magnitude, and the capacitance between the source and outer surrounding boundaries. [Preview Abstract] |
Tuesday, October 6, 2020 9:15AM - 9:30AM Live |
FT4.00006: Measurement of non-linear coupling and energy transfer in plasma turbulence in a Hall effect thruster Zachariah Brown, Benjamin Jorns The nonlinear coupling coefficient and the energy transfer from multi-wave interactions are determined from measurements of plasma turbulence in a Hall effect thruster. The crossed electric and magnetic fields in Hall thrusters generate a large electron velocity, while the ions are relatively stationary, that gives rise to an instability known as the Electron Drift Instability (EDI). It is theorized that this instability is responsible for the anomalously high electron mobility across magnetic fields observed in these devices. Recent particle-in-cell simulations have demonstrated that this wave driven transport is strongest due to oscillations at long wavelengths that develop from a non-linear energy cascade from the initial, small wavelengths. Using the analysis technique of Ritz, we experimental show that this theorized non-linear effect does occur in these devices. [Preview Abstract] |
Tuesday, October 6, 2020 9:30AM - 9:45AM |
FT4.00007: Line Integrated Barium Absorption Spectroscopy For Hollow Cathodes Nathaniel Wirgau, John Foster The lifetime of the HCA in many cases determines the overall lifetime of the thruster. The lifetime of cathodes is dependent upon the state of the emitter surface, characterized by a mean work function. Due to various processes including depletion of emitter material, the work function of the emitter tends to increase over time, ultimately ending in emitter failure at practical emission temperatures. Future thrusters will require higher emission currents from their HCA than the currently attainable. Physics based simulation of HCA operation have the potential as a tool to understand both the uncertainty and sensitivity of life-limiting processes. Howerver, the physics within the model must be verified and then the model bench-marked against simple cases. The model must also be tested against experiment for predictive validation. In this work, we gain insight into the evolution of the barium supply within the insert region of an HCA. Through the use of absorption spectroscopy and given that barium density is high enough to adequately discriminate signal from noise, we obtain a line-integrated measure of the neutral barium density during cathode operation as a first step towards quantifying barium transport in the insert region. Here we present the progress of this work. [Preview Abstract] |
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