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A 0D model for an iodine-fed Hall thruster is presented. A complete set of reactions is used to account for iodine plasma chemistry phenomena and trace the presence of multiple neutrals and ionized species. The model is developed using novel assumptions based on experimental data trends as derived from the literature. The simulation domain is divided into two zones in order to refine the iodine molecule dissociation process localized in the low electron temperature region found upstream in the channel. After validating a xenon version of the model against SPT-100 characteristics, numerical results are compared against experimental data relative to a low-power iodine-fed Hall thruster. Discharge current and thrust are predicted with satisfactory quantitative agreement, and overall trends are effectively captured. The numerical results indicate a relatively large portion of ionized molecules, while negative ions appear to occur in non-negligible amount upstream in the thruster channel. [ABSTRACT FROM AUTHOR]

The performance characteristics of an argon propellant Hall thruster with two types of propellant injectors, the axial and swirl injectors, were investigated. In the swirl injector, the propellant is injected in the tangential direction. At a discharge voltage of 150 V, the swirl injector achieved a higher propellant utilization efficiency (30.3%) and anode efficiency (8.8%) compared to the axial injector (26.7% and 7%, respectively). A numerical simulation quantitatively explained the reason for these differences, which shows an increase in the neutral particle density of 32.6% near the injection region and 7.8% at the exit of the hollow anode with the swirl injector. Neutral particle accommodation on the anode wall was found to be the predominant mechanism, which reduces the injection effect. [ABSTRACT FROM AUTHOR]

This study uses concurrent spectroscopic measurements that provide evidence of the predator–prey behavior between ions, neutral atoms, and electrons that is theorized to drive the Hall thruster breathing mode, a crucial oscillation in Hall thrusters impacting their efficiency and stability. A novel fast optical emission spectroscopy diagnostic is employed to simultaneously measure the characteristics of neutral and ion populations through their respective emissions. A quasi-1D predator–prey model of the breathing mode is utilized to predict the phase difference between neutral and ion populations according to the predator–prey theory. The observed phase difference between Xe I and Xe II emissions is consistent with the expected phase difference between neutral and ion populations predicted by the quasi-1D model. Several operating conditions are explored, and the impact of adjusting the plasma conditions are explored both through experiments and modeling. [ABSTRACT FROM AUTHOR]

The axial distribution of the electron density and temperature in the discharge plasma of a water-vapor Hall thruster is measured by a cylindrical Langmuir probe using a fast-moving system. They are evaluated in two ways; by integrating full trace of the measured electron energy distribution function (EEDF) and by fitting a Maxwellian EEDF to the low-energy part of the measured EEDF. The ion current density for each species produced by electron-impact ionization is estimated using the obtained electron density and temperature. It is revealed that OH + and H + can be contained other than H 2 O + with non-negligible fractions, causing an additional 20%–25% loss of the anode efficiency estimated by the plume diagnostics. It is also suggested that elastic momentum transfer, electronic excitation, and dissociation to the neutral fragments are more dominant processes than ionization, whereas the electron attachment, rotational excitation and vibrational excitation are minor events among the electron-impact reactions. The subsequent ionization processes from the neutral fragments are also expected to play an important role in determining the effective design and operating parameters for further improvement of the mass utilization efficiency. [ABSTRACT FROM AUTHOR]

Many plasma systems and technologies, such as Hall thrusters for spacecraft propulsion, exhibit complex underlying physics that affect the global operation. When characterizing such systems in an experiment, obtaining full spatiotemporal maps of the involved state variables can be, thus, highly informative. However, this goal is not practically realizable because of various experimental limitations, e.g., finite spatial resolution of the diagnostics and geometrical accessibility constraints. Therefore, having the capability to reconstruct the full high-dimensional states of plasma systems from low-dimensional time-history measurements is greatly desirable. Compressed sensing is a signal processing technique that can answer this crucial need. However, existing compressed sensing approaches have several limitations that restrict their effectiveness for complex physical systems like plasma technologies. These include the need for abundant sensor measurements and a principled sensor placement. In this paper, we demonstrate the capabilities of Shallow Recurrent Decoder (SHRED) architecture for compressed sensing. We show in several plasma test cases that SHRED can robustly infer full high-dimensional spatiotemporal state vectors of these systems (i.e., all macroscopic plasma properties) from minimal system information. This minimal information can consist of three finite time-history measurements of either local values of a plasma property or the global plasma properties (spatially averaged or performance parameters). An application of SHRED's inference capability in the numerical plasma simulation context is "super-resolution" enhancement. We will discuss this application by presenting how SHRED can effectively establish mappings between a low-resolution and a high-resolution simulation, recovering detailed spatial plasma features that are below the simulation's grid size. [ABSTRACT FROM AUTHOR]

This study presents a proof-of-principle for using optical emission spectroscopy and artificial neural networks for real-time monitoring and control of the operational parameters of a Hall effect thruster: the anode voltage, the anode xenon injection, the discharge current, and the coil current. In that regard, we build an optical database of 26 spectral lines across 6469 operating conditions to train and test the neural network. We then reduced the learning lines from 26 to 15 based on their statistical correlation with the target parameters. After tuning the hyperparameters of the network, the network predicted the thruster's parameters with notable accuracies: 95% for the anode voltage, 84% for the coil current, and 99% for both the anode flow rate and the discharge current. The estimated uncertainty of predictions, at 3 σ , is ± 51 V for voltage, ± 1 A for coil current, ± 0.15 A for discharge current, and ± 0.15 mg s − 1 for anode flow rate. The prediction calculations were within milliseconds and enabled real-time monitoring of the thruster parameters. Therefore, a proportional-integrator-derivative controller (PID) controller was implemented to regulate the anode voltage and flow rate based on the optical emission of the plume. The PID showcased short settling times from 0.1 to 0.4 s and overshoot levels up to 3% of the target value for the voltage and 10% of the target value for the flow rate. These results were for a fixed coil current at 4 A. The study showed that changing the coil current may necessitate more sophisticated prediction models and control strategies. Future work will expand the model's generalizability to different thruster types, propellants, and magnetic field configurations. [ABSTRACT FROM AUTHOR]

Magnetically shielded Hall effect thrusters suffer from pole erosion as their life-limiting mechanism. However, the dominant physical mechanism causing this erosion remains unclear, limiting the ability create designs that mitigate erosion and the predictive accuracy of simulations used to aid in design. This paper provides spatially resolved laser Thomson scattering measurements of electron temperature and density in the near field plume of a magnetically shielded Hall effect thruster, traversing the front pole region from the discharge channel centerline to the cathode centerline. The signals are inverted in a Bayesian framework, and the data are compared qualitatively and quantitatively to simulations of the same Hall effect thruster. Based on the electron momentum equation, electron pressure gradient is used as a proxy for the electron-predicted electrostatic potential gradient. To within the accuracy of this approximation, the electron pressure has a minimum immediately in front of the front pole. Hence, ions have an electrostatic potential avenue from the discharge region to the front pole, validating this mechanism of pole erosion. [ABSTRACT FROM AUTHOR]

Noninvasive measurements of electron properties in a Hall effect thruster (HET) are needed to understand the physical processes in the acceleration region and to validate simulations. This paper presents spatially resolved laser Thomson scattering (LTS) measurements across the entire acceleration region of a HET. The test article is the H9, a 9 kW class magnetically shielded HET. The H9 is operated on krypton at a facility pressure of 1.2 × 10−5 Torr Kr (1.6 mPa). The thruster is operated at three discharge conditions: 171 V, 35 A, an inner coil current (Iic) of 4.11 A, and an outer coil current (Ioc) of 2.27 A as the baseline 6 kW condition; 154 V, 34.8 A, an Iic of 4.11 A, and an Ioc of 2.27 A to vary the discharge voltage; and 171 V, 34.4 A, an Iic of 4.52 A, and an Ioc of 2.5 A to vary the magnetic field strength. At each discharge condition, we measured axial profiles of electron density and electron temperature along the channel centerline from 5% to 95% of a channel length downstream of the channel exit plane. At the baseline condition, we also measure the axial profile of the azimuthal electron drift velocity. We measure a minimum electron density of 1.3 × 1017 m−3, peak electron temperatures around 40 eV, and a peak azimuthal electron drift velocity around 680 km/s. The results suggest the presence of anomalous electron heating and demonstrate that low discharge voltages allow LTS to access the entire acceleration region of a HET. [ABSTRACT FROM AUTHOR]

An experimental evaluation is presented of a two-equation model for the low frequency (< 25 kHz), large amplitude (> --> 100 % of mean) discharge oscillations exhibited by a 9-kW class magnetically shielded Hall thruster. The model is based on a theoretical treatment of the "breathing mode" oscillations in Hall thrusters (Barral and Peradzyński, "A new breath for the breathing mode," IEPC-2009-070) and includes governing equations for fluctuations in the discharge current and the spatially averaged neutral density in the thruster channel. The derivation of the governing equations is reviewed, and the key simplifying assumptions are formulated in terms of comparisons between the magnitudes of relative fluctuations in spatially averaged plasma properties. Experimental measurements are performed of these plasma properties at an operating condition of 300 V discharge voltage and 10 A discharge current. It is found that all quantities of interest such as drift speed, electric field, and temperature fluctuate on the timescale of the low frequency oscillations. However, the relative phasing of these properties combine in such that the key assumptions of the model are satisfied—all but the neutral density and discharge fluctuations can be neglected in the equations for neutral density and current oscillations. A physical interpretation of the validity of the assumptions is presented, and the model is discussed in the context of its extensibility to other operating conditions. The validated model forms the basis for a parametric study presented in Part II of mode transitions and the criterion for these transitions in a magnetically shielded Hall thruster. [ABSTRACT FROM AUTHOR]

A stability criterion is derived for mode transitions in the discharge current oscillations of a magnetically shielded Hall thruster. The two-equation model evaluated in Paper I for these large-amplitude (> --> 100 % background), low-frequency (< 25 kHz) current oscillations is generalized and then validated with measurements from a 9 kW class test article. It is shown that the model can re-create quantitatively trends in both oscillation amplitude and frequency with discharge voltage and current. The validated model is non-dimensionalized and applied to derive an analytical stability criterion for the onset of large-amplitude oscillations. The resulting expression depends on several properties, including discharge current, discharge voltage, neutral transit time in the channel, length of the acceleration zone, magnetic field strength, and channel area. The criterion is leveraged to inform two mitigation strategies—changing magnetic field strength and controlling anode temperature— for adjusting the stability margin of the thruster. The criterion is also employed to motivate a physical explanation for why mode transitions occur and, in turn, why the stability margin differs between shielded and unshielded thrusters. [ABSTRACT FROM AUTHOR]

A fully cylindrical Hall thruster prototype was tested in the power range of 30–300 W with the objective of understanding the behavior of the discharge as a function of input parameters. Various operating conditions were compared, including two magnetic field configurations, a set of propellant mass flow rates, and a range of discharge voltages. Plasma properties were measured in the plume, with a Langmuir probe, a retarding potential analyzer, and a Faraday cup. The experimental results showed that the mass flow rate strongly affects the ionization and, consequently, other related properties such as the plasma density, currents, and propellant utilization. The discharge voltage also appeared to influence the ion energy and propellant utilization. The performance accessible from the measured magnitudes is assessed, resulting in a maximum thrust efficiency of about 18% at 0.35 mg s − 1 and 168 W. [ABSTRACT FROM AUTHOR]

Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent "spot mode" and in a noisy "plume mode" in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements. [ABSTRACT FROM AUTHOR]

We use a 2.5D hybrid simulation to study the breathing mode (BM) dynamics in Hall thrusters (HTs). This involves a 1D Euler fluid simulation for neutral dynamics in the axial direction, coupled with a 2D axial–azimuthal Particle-in-Cell (PIC) simulation for charged species. The simulation also includes an out-of-plane virtual dimension for wall losses. This setup allows us to replicate the BM's macroscopic features observed in experiments. A comprehensive analysis of plasma parameters in BM's phases divides it into two growth and two decay sub-phases. Examining 1D axial profiles of electron temperature, gas and plasma densities, and particle creation rate shows that an increase in electron temperature alone cannot sustain ionization. Ionization seems to be influenced by the spatial correlation between electron and gas densities and the ionization rate coefficient. Investigating ion back-flow reveals its impact on modulating neutral flux entering the ionization region. The hybrid simulation's outcomes let us assess the usual 0D predator–prey model's validity and identify its limitations. The ionization and ion convection term approximations hold, but the gas convective term approximation does not. Introducing an alternative gas convective term approximation involving constant density ejection from the ionization region constructs an unstable BM model consistent with simulation results. In addition, this paper explores how varying the imposed voltage and mass flow rate impacts the BM. The BM frequency increases with imposed voltage, aligning with theoretical predictions. The mass flow rate variation has a limited effect on BM frequency, following the theoretical model's trend. [ABSTRACT FROM AUTHOR]

The topology of the applied magnetic field is an important design aspect of Hall thrusters. For modern Hall thrusters, the magnetic field topology most often features curved lines with a concave (negative) curvature upstream of the field's peak and a convex (positive) curvature downstream. Additionally, the advent of the magnetic shielding technique has resulted in Hall thruster designs with non-conventional field topologies that exhibit high degrees of concavity upstream of the field's peak. In this article, a detailed study is carried out on the effects that the magnetic field curvature has on the plasma discharge in a 2D configuration representative of a Hall thruster's radial–azimuthal cross section. The analyses are performed for discharges of three propellants of high applied interest: xenon, krypton, and argon. For each propellant, high-fidelity electrostatic reduced-order particle-in-cell (PIC) simulations are performed with various degrees of positive and negative curvatures of the magnetic field. Corresponding 1D radial PIC simulations are also performed for xenon to compare the observations against the 2D results. Most notably, it is observed that the instability spectra in the positive-curvature cases are mostly dominated by electron cyclotron drift instability, whereas the modified two stream instability is dominant in the negative-curvature cases. The distributions of electron and ion temperatures, in particular, as well as the contribution of various mechanisms to electrons' cross-field transport show notable variations between the positive and negative curvature values. Finally, the field curvature is observed to majorly influence the ion beam divergence along the radial and azimuthal coordinates. [ABSTRACT FROM AUTHOR]

Hall thrusters are electric propulsion devices widely used on spacecraft. The stability of Hall thrusters is often disturbed by low-frequency oscillations (LFOs) around 5–100 kHz, known as the 'breathing mode', typically observed through fluctuations in channel discharge current and plasma parameters. Experimental studies on Hall thrusters with a wide range of sizes show that LFOs exhibit distinct characteristics depending on the channel structures. The size of the channel can modify the particle-wall interactions, electric potential distribution, and electron temperature, thereby influencing the performance of LFOs. Furthermore, the long-term operation of thrusters can cause significant wall erosion, altering the geometry of the discharge channel, which further impacts LFOs. In this work, a one-dimensional fluid model is established to explore the influences of structure sizes and wall erosion of the channel on the LFO characteristics. Both the thruster channel and the plume region are included in the model, and a modified and more precise approach to calculating the electron energy loss at the wall is proposed, which takes into account the influences of secondary electron emission and the channel cross-sectional area. The simulation results indicate that choosing a narrower or longer channel structure has a significantly suppressing effect on LFOs. An erosion model is established according to the cited experimental data to construct the eroded channel structure and to investigate the effect of channel erosion on the breathing mode, which shows that wall erosion can exacerbate LFOs and impact the performance of the thruster. [ABSTRACT FROM AUTHOR]

The following paper reports about a non-intrusive diagnostic system able to measure the frequency of azimuthal instabilities inside the discharge channel of Hall Effect Thrusters (HETs) up to several hundreds of kHz in a real-time fashion. The innovative optical assembly, formed by an optimized sensor array, can help to drastically reduce the amount of processed data and the size of the opto-electronic front-end. The performances of the diagnostic system have been tested successfully during several tests on a HET in different regimes, showing an accuracy and reliability comparable with the state-of-the-art video recording methods. In order to test the real-time fashion of the diagnostic, we have monitor the time-evolution of the azimuthal mode spectra during the startup transient of the thruster, highlighting a redistribution of the oscillation energy among the different mode to an asymptotic stationary regime. The high compactness of the developed sensor array opens new possibilities to perform simultaneously multi-channel or species-selective real-time measurements, while the reduced electronics and power consumption pave the way to miniaturized tools for on-flight diagnostics. [ABSTRACT FROM AUTHOR]

A previous companion paper introduced a current pathways model that represents the electrical coupling between the Hall effect thruster (HET) and the ground-based vacuum test facility operational environment. In this work, we operated a 7-kW class HET at 4.5 kW, 15 A and 6 kW, 20 A on krypton to quantify aspects of the current pathways model to characterize the role metal vacuum chambers play in the thruster's discharge circuit as a function of discharge current. During HET operation, far-field ion and electron saturation currents at 47 near-facility wall locations were measured using an array of 5.08 cm diameter, stainless-steel planar electrodes. In addition, the plasma properties at three distinct locations within the facility, 25 cm from the facility wall, were obtained using Langmuir probes. Experimental results show that thruster beam ions do not readily neutralize with cathode electrons and instead neutralize with the free electrons provided by the metallic chamber wall. In addition, significant charge-exchange (CEX) ion current was measured in the background plasma environment and constituted about 23% of the total ion current measured by the planar electrode array. Thus, the metallic vacuum chamber surfaces facilitate charge neutralization for both ion populations. Additionally, the plasma environment near the facility walls was characterized to be non-uniform with an estimated plasma sheath capacitance ranging between 0.45 µF and 1.79 µF. Further analysis shows that the plasma sheath at the facility wall behaves like a parallel RC circuit, potentially concealing the thruster's AC characteristics. Inherent plasma oscillations give rise to inductive effects with inductances that varied between 76.5 nH and 101.4 nH. Hence, the dynamic characteristics of the HET's discharge are influenced by the capacitive and inductive effects introduced by the vacuum test facility operational environment. [ABSTRACT FROM AUTHOR]

Hall effect thrusters (HETs) are typically regarded as DC electric propulsion devices as they are operated with isolated DC power supplies. However, it is well known that the HET's discharge current possesses oscillations of varying magnitudes and frequencies and is thus a function of time with AC characteristics. The observed oscillations are caused by plasma processes associated with ion, electron, and neutral particle dynamics that occur inside the HET's discharge channel and in the plume as the HET electrically interacts with its local operating environment. The extent to which plasma oscillations impact HET discharge dynamics is difficult to quantify due to the complexity of analyzing AC signals, given that the HET is a nonlinear, time-variant electrical load. In this work, we overcome the challenge of nonlinearity and time-variance of HETs by conducting a small-signal impedance analysis to characterize the effective resistance and reactance of the HET discharge with a novel and versatile impedance measurement diagnostic. The impedance magnitude and phase of a 7-kW class HET were measured from 100 Hz to 300 kHz with an excitation signal of ± 2 Vpk for two discharge operating conditions on krypton: 4.5 kW, 15 A and 6 kW, 20 A. The results were used to quantify resistive, capacitive, and inducive characteristics present within the HET discharge signature. For the 4.5 kW, 15 A thruster operating condition, the breathing mode capacitance was estimated to be 12.6 µF with an inductance of 15.3 µH. Furthermore, the impedance characteristics of the breathing mode are within ± 2.4 kHz of the power spectral density plots independently generated by time-resolved oscilloscope traces indicating good agreement in the frequency domain. Thus, the impedance measurement tool is a new diagnostic for characterizing the impedance and associated AC characteristics of HETs. [ABSTRACT FROM AUTHOR]

This paper presents a technique for reconstructing the temporal evolution of ion distribution functions (IDF) in a Hall thruster using ion currents measured with a retarding potential analyzer. The method involves averaging discharge oscillations with temporal realignment based on the maxima of the discharge current. This technique was applied to ion currents from the experimental ID-Hall 2 thruster, successfully reconstructing the time-dependent ion distribution function in quasi-periodic plasma oscillation regimes. The results indicate that deformations in the integrated ion distribution function can be attributed to the IDF's temporal evolution over a characteristic time equal to the breathing mode oscillation period. This finding suggests the possibility of uncoordinated displacement of ionization and acceleration zones within the discharge. In certain oscillation regimes, the oscillations in ion transit time also appear to have a minor effect on ion acceleration. [ABSTRACT FROM AUTHOR]

The Air-breathing Microwave Plasma CAThode (AMPCAT) has been developed for air-breathing electric propulsion in very-low Earth orbit. In this study, the standalone AMPCAT plasma characteristics are analyzed by means of several diagnostic tools and operation on xenon is compared to a conventional hollow cathode. A transition of AMPCAT extracted current from a lower (< 0.1 A) to higher-current (> --> 0.5 A) mode, triggered by increasing the negative cathode bias voltage, is accompanied by a significant rise in internal electron density and external electron temperature. The AMPCAT is coupled with a cylindrical Hall thruster in the 100–300 W power-level running on 0.5–0.7 mg/s of xenon, and the thrust is directly measured for cathode operation with both xenon and air. Stable thruster operation is demonstrated for the AMPCAT running on both propellants. For xenon, the performance is compared to a hollow cathode, which reveals matching discharge current profiles but a significantly higher thrust for the AMPCAT at low discharge voltages, approximately two times higher at 200 V. Langmuir probe measurements highlight a 30–40 V lower plasma potential in the cathode vicinity for the AMPCAT with xenon compared to both the hollow cathode and AMPCAT with air. This indicates a significantly improved coupling of cathode electrons to the thruster discharge, yielding an increased degree of ionization. Faraday probe and Wien filter results show that a larger current utilization efficiency drives the observed performance difference at low discharge voltages, rather than a significant change in ion acceleration or plume divergence. [ABSTRACT FROM AUTHOR]

The behavior of four algebraic closure models for anomalous electron transport is investigated using a fluid Hall thruster code. The models, which were selected because they have been previously described in the literature, are calibrated against a baseline experimental condition of a 9-kW-class magnetically shielded Hall thruster operating at 300 V and 15 A on xenon propellant. The extensibility of the models is then assessed by using this calibrated model to simulate three additional operating conditions—300 V and 30 A, 600 V and 15 A, and 300 V and 15 A operating on krypton propellant. The quality of the model prediction is quantified by comparing the model outputs to experimental measurements of discharge current, thrust, and ion velocity. It is found that while none of the models can predict the ion acceleration characteristics accurately, some compare favorably in terms of the scaling of thrust and discharge current across operating conditions. The limitations of the models are attributed to the coupling between the functional scaling of the closure models with respect to the local plasma properties and the fluid model. The role of the electron energy balance in this coupling is also highlighted. These results are discussed in the context of motivating improved closure models of the anomalous electron transport in Hall thrusters. [ABSTRACT FROM AUTHOR]

The effects of anode voltage and mass flow rate on the erosion of the inner permanent magnet conducting cover in a 100 W Hall thruster were studied in this paper. To accelerate erosion, an inner permanent magnet conducting cover made of aluminum alloy was employed. Experimental results indicate that the erosion rate of the inner conducting cover increases with higher anode voltage and mass flow rate. When the anode mass flow rate is set at 3.8 sccm and the anode voltage increases from 200 V to 300 V and 350 V, the erosion rate at the center of the inner conducting cover increases from 6.54 mm kh−1 to 9.29 mm kh−1 and 13.79 mm kh−1, respectively, reflecting increases of 42.0% and 110.8% compared to the initial erosion rate. When the anode voltage is 200 V and the anode mass flow rate increases from 3.8 sccm to 5.4 sccm and 6.9 sccm, the erosion rate at the center of the cover increases from 6.54 mm kh−1 to 9.00 mm kh−1 and 10.91 mm kh−1, indicating increases of 37.6% and 66.9%, respectively. These findings underscore the challenges of maintaining the lifespan of the inner conducting cover when thruster is operated under the conditions of high specific impulse and high thrust discharge. Further investigation reveals that the potential difference between the channel exit and the inner conducting cover is a significant factor driving ions near the channel exit bombardment of the inner conducting cover. Increased anode voltage and mass flow rate enhance this potential difference and increase the ion density near the channel exit, resulting in greater current density and energy of ions bombarding the inner conducting cover, thereby accelerating its erosion. This study provides a reference for the lifespan analysis of the inner conducting cover in low-power thrusters operating under multi-mode conditions. [ABSTRACT FROM AUTHOR]

The dynamics of the neutral atoms in Hall thrusters affects several plasma processes, from ionization to electrons' mobility. In the context of Hall thruster's particle-in-cell (PIC) modeling, the neutrals are often treated kinetically, similar to the plasma species, and their interactions with themselves and the ions are resolved using the direct-simulation Monte–Carlo (DSMC) algorithm. However, the DSMC approach is computationally resource demanding. Therefore, modeling the neutrals as a 1D fluid has been also pursued in simulations that do not involve the radial coordinate and, hence, do not resolve the neutrals' radial expansion. In this article, we present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics. We carried out 1D axial PIC simulations with various fluid and kinetic models of the neutrals as well as self-consistent quasi-2D axial-azimuthal simulations with different neutrals' fluid descriptions. Our results show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of the neutrals change the spatiotemporal evolution of the discharge. Moreover, we observed that considering the ion-neutral collisions causes a significant variation in the neutral temperature, thus requiring that the neutrals' energy equation to be included as well in their fluid system of equations. Finally, the self-consistent axial-azimuthal simulations highlighted that a neutrals' model based on the continuity conservation equation only is not an appropriate choice and leads to physically unexpected high-frequency global discharge oscillations. [ABSTRACT FROM AUTHOR]

Expected high electron mobility and low resistivity along magnetic field lines—as compared to across magnetic field lines—have led to the assumption, or the reproduction through a solution to the electron energy equation, that magnetic field lines are isothermal in typical plasma simulations for Hall effect thrusters (HETs). However, the inaccessibility of the near-field plasma region and perturbative nature of electrostatic probes have prevented validation of these assumptions in HETs. This manuscript presents non-intrusive measurements of the electron number density and electron temperature along two distinct magnetic field lines in the near-field discharge of a magnetically shielded HET operating at 150 V and 40 A on krypton based on incoherent laser Thomson scattering. The resulting electron temperature and density profiles indicate that the magnetic field lines are not isothermal or isopotential, with percent changes exceeding 100% of the channel centerline electron temperature along each magnetic field line. This observation brings into question the current state of electron models in simulations and what physics are included, or neglected, to produce isothermal magnetic field lines in certain regions. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) is an attractive candidate for condensable propellants because its availability and storability. Although several studies have been reported on adopting CO 2 as a propellant for Hall thrusters, there have been few studies on CO 2 standalone operation, and none of them have focused on physical phenomena in plasmas. This study experimentally evaluated, thrust performance and plume characteristics of a 100 W-class Hall thruster under CO 2 operation. CO 2 operation was compared to xenon operation under the same discharge power conditions to determine its unique properties. As typical thrust performance under this experimental condition, a specific impulse of 727 s, thrust-power-ratio of 19.8 mN/kW, and anode efficiency of 0.0711 were achieved at a discharge voltage of 200 V and a discharge power of 352 W under a background pressure of 3.4 × 10−2 Pa. Plume measurements showed that mass utilization efficiency was 0.228 under CO 2 operation, which was particularly poor compared to under xenon operation. The first reason for this is that the ionization mean free path of CO 2 is 5.18 mm, about eight times longer than that of xenon. The second reason is that the energy is used for other processes, such as dissociative ionization and dissociation etc., considering the reaction process of the particles. Therefore, the results suggest narrowing the channel width to increase the channel density, and increasing the magnetic field strength to suppress the discharge current as ways to improve thrust efficiency. • A 100 W-class Hall thruster was operated under CO 2 conditions. • Thrust performance and plume characteristics were evaluated. • The anode efficiency under CO 2 operation was 0.0711, which 40 % of xenon. • Low anode efficiency was attributable to low mass utilization efficiency. • A method to improve mass utilization efficiency, narrowing the channel width is suggested. [ABSTRACT FROM AUTHOR]

Effects of the propellant, propellant mass-flow rate, and discharge voltage on the characteristics of the plume of small Hall thrusters are studied using a particle-in-cell Monte Carlo collisions program. It is shown that with the same discharge voltage and mass flow, the divergence angle of the xenon plume is smaller than that of argon and is not linearly dependent on the propellant mass flow rate. Moreover, the effect of the discharge voltage on the plume divergence angle can be significant. As the discharge voltage increases from 100 to 300 V, the plume divergence angle decreases, but in the range 300–400 V, it increases with the discharge voltage. The obtained data can be useful for the design and improving the efficiency of Hall thrusters. [ABSTRACT FROM AUTHOR]

A discharge in the annular cavity of a Hall effect thruster is sustained by extracting electrons from a radiofrequency (rf) inductively coupled plasma source located downstream of the thruster structure, where a radial magnetic field of 0.1-0.15 T is applied to the thruster discharge cavity by permanent magnets. Argon gas is introduced into the cavity via an anode structure and the ejected gas passes through the rf plasma source powered by a 13.56 MHz and 200 W generator. After turning on the rf plasma, a dc voltage is applied between a cathode installed inside the rf source and the anode of the Hall effect thruster, creating the bright annular discharge in the cavity. Measured ion energy distribution functions contain the energetic ions having the maximum potential close to the anode potential, demonstrating the ion acceleration from the annular cavity and the neutralization by the electrons in the rf plasma source. [ABSTRACT FROM AUTHOR]

We study the analysis and refinement of a predictive engineering model for enabling rapid prediction of Hall thruster system performance across a range of operating and environmental conditions and epistemic and aleatoric uncertainties. In particular, we describe an approach by which experimentally-observed facility effects are assimilated into the model, with a specific focus on facility background pressure. We propose a multifidelity, multidisciplinary approach for Bayesian calibration of an integrated system comprised of a set of component models. Furthermore, we perform uncertainty quantification over the calibrated model to assess the effects of epistemic and aleatoric uncertainty. This approach is realized on a coupled system of cathode, thruster, and plume models that predicts global quantities of interest (QoIs) such as thrust, efficiency, and discharge current as a function of operating conditions such as discharge voltage, mass flow rate, and background chamber pressure. As part of the calibration and prediction, we propose a number of metrics for assessing predictive model quality. Based on these metrics, we found that our proposed framework produces a calibrated model that is more accurate, sometimes by an order of magnitude, than engineering models using nominal parameters found in the literature. We also found for many QoIs that the remaining uncertainty was not sufficient to account for discrepancy with experimental data, and that existing models for facility effects do not sufficiently capture experimental trends. Finally, we confirmed through a global sensitivity analysis the prior intuition that anomalous transport dominates model uncertainty, and we conclude by suggesting several paths for future model improvement. We envision that the proposed metrics and procedures can guide the refinement of future model development activities. [ABSTRACT FROM AUTHOR]

Probe diagnostics of ion energy distribution and ion current density in the plasma plume of electric propulsion is considered. A detailed numerical and experimental comparison is presented of a new, high dynamic range retarding potential analyzer (HDR RPA) and a conventional gridded RPA probe applied to a plume of a hall effect thruster (HET) operating in different modes. Simulations show the disadvantages of the gridded retarding potential analyzer design and the advantages of the HDR RPA. By means of numerical modeling, the peculiarities of using the HDR RPA are also investigated in detail and preliminary conclusions regarding the probe accuracy are drawn. The final part of the paper shows the results of joint tests of the two probes at those plasma parameters where the gridded probe works most accurately, with a confirmed maximum error of 5%. [ABSTRACT FROM AUTHOR]

Hall thrusters are one of the most successful and prevalent electric propulsion systems for spacecraft in use today. However, they are also complex devices and their unique E × B configuration makes modeling of the underlying plasma discharge challenging. In this work, a steady-state model of a Hall thruster is developed and a complete analytical solution presented that is shown to be in reasonable agreement with experimental measurements. A characterization of the discharge shows that the peak plasma density and ionization rate nearly coincide and both occur upstream of the peak electric field. The peak locations also shift as the thruster operating conditions are varied. Three key similarity parameters emerge that govern the plasma discharge and which are connected via a thruster current–voltage relation: a normalized discharge current, a normalized discharge voltage, and an amalgamated parameter, α ¯ , that contains all system geometric and magnetic field information. For a given normalized discharge voltage, the similarity parameter α ¯ must lie within a certain range to enable high thruster performance. When applied to a krypton thruster, the model shows that both the propellant mass flow rate and the magnetic field strength must be simultaneously adjusted to achieve similar efficiency to a xenon thruster (for the same thruster geometry, discharge voltage, and power level). [ABSTRACT FROM AUTHOR]

Plasma propulsion, or electric propulsion, arises from the need to explore deep space more economically and efficiently. The Cylindrical Hall Thruster (CHT) demonstrates enhanced propellant utilization and performance efficiencies within reduced dimensions and lower power thresholds when compared to conventional plasma propulsion apparatuses. The compact size and operation at lower power levels make it an interesting option to provide propulsion for CubeSats and small satellites. The CHT comprises a channel with an annular anode through which neutral gas is injected, subsequently ionized by magnetized electrons injected from an external hollow cathode. The resulting plasma ions are ejected from the device, giving thrust. This work aims to understand and study the plasma in the discharge channel of a CHT through numerical simulations. The code describes the plasma with a hybrid model in which the electrons are treated as a fluid and the ions and neutral atoms as pseudo particles. The simulations were conducted for two different potential values at the anode, specifically 150 V and 300 V, representing different modes of operation. The results obtained with this simplified model allow obtain an optimal configuration for a future prototype to be implemented at the Plasma Physics Laboratory at the University of Brasilia. [ABSTRACT FROM AUTHOR]

Partially magnetized low-temperature plasmas (LTP) in an E × B configuration, where the applied magnetic field is perpendicular to the self-consistent electric field, have become increasingly relevant in industrial applications. Hall thrusters, a type of electrostatic plasma propulsion, are one of the main LTP technologies whose advancement is hindered by the not-fully-understood underlying physics of operation, particularly, with respect to the plasma instabilities and the associated electron cross field transport. The development of Hall thrusters with unconventional magnetic field topologies has imposed further questions regarding the instabilities' characteristics and the electrons' dynamics in these modern cross field configurations. Accordingly, we present in this effort a detailed parametric study of the influence of three factors on the plasma processes in the radial-azimuthal coordinates of a Hall thruster, namely, the magnetic field gradient, secondary electron emission, and plasma number density. The studies are carried out using the reduced-order particle-in-cell code developed by the authors. The setup of the radial-azimuthal simulations largely follows a well-defined benchmark case from the literature in which the magnetic field is oriented along the radius, and a constant axial electric field is applied perpendicular to the simulation plane. The salient finding from our investigations is that, in the studied cases corresponding to elevated plasma densities, a long-wavelength azimuthal mode with the frequency of about 1 MHz is developed. Moreover, in the presence of strong magnetic field gradients, this mode results from an inverse energy cascade and induces a significant electron cross field transport as well as a notable heating of the ions. [ABSTRACT FROM AUTHOR]

Venμs is a satellite launched in 2017, for super-spectral Earth imaging and Electric Propulsion System (EPS) demonstration. In this paper we overview EPS design and operation throughout all five mission phases, from open/closed-loop orbit control, through orbit descent (720 → 410 km), orbit maintenance under high drag environment, to orbit raising (410 → 560 km). The EPS consisted of two throttleable Hall thrusters, PPU, Propellant Management Assembly (PMA), and a 9 L propellant tank carrying 16 kg of Xenon. Both thrusters operated in the 300–550 W power range, generated a combined total impulse of 158.1 kN-sec and consumed all propellant. Two methods are described to compute the remaining propellant mass – "Bookkeeping" and "PTV" methods. The advantages and disadvantages of each method are discussed in light of the Venµs mission. Thruster performance was measured on-orbit using the "Orbit Determination" method and compared to laboratory experiments conducted on the ground with identical thrusters. The measured performance on-orbit was found to agree within the error bars with the performance measured on the ground. Lastly, we present several repeating events in which the propulsion system suffered from sudden beam-outs or ignition difficulties. We present the methods used to construct a solution and implement it. [ABSTRACT FROM AUTHOR]

Utilizing alternative propellants has been recognized as a strategy to reduce the total cost of propellants in electric propulsion-based missions. The aim of this study is to quantify the Hall effect thruster (HET) performance and operating characteristics using a Kr–Ar mixture to enable mission designers to evaluate the impact on mission and spacecraft design. We present the performance and plume plasma properties of the P5 5 kW-class HET operated with a Kr–Ar mixture with Ar volumetric flow rate fractions from 0 to 100%. The thruster is characterized at discharge power levels of 2.6 kW and 4.1 kW at constant discharge current and voltage over the range of Ar fractions. Despite higher ionization energy and lower mass of Ar, the thruster exhibited a similar level of thrust within 2% when comparing the pure Kr and 26%-Ar mixture cases. The derived ion energy distribution functions and analytical modeling suggest that the characteristic length for the ionization region is extended as the Ar fraction increases. The increased residence time of Kr at the extended ionization region and background energetic electrons from the ionized Ar neutrals are considered to cause this enhanced ionization of the injected Kr neutrals. This leads to a 6% higher Kr ion density at the 26%-Ar case even at the 16% less injected Kr neutral density than in the pure Kr case. The enhanced Kr ionization and generated Ar ions in the 26%-Ar case consequently led to a comparable thrust with that of the pure Kr case. The study indicates that mixing Ar with approximately 26% volumetrically with Kr can provide a similar or even higher thrust performance at the same discharge power. This will be particularly advantageous for various space missions that require high impulses by reducing the total cost of the propellant. [ABSTRACT FROM AUTHOR]

The azimuthal dynamics of ions along the inner pole of a Hall thruster with a centrally mounted cathode and a magnetic shielding topography are experimentally investigated. A time-averaged laser-induced fluorescence diagnostic is implemented to characterize the azimuthal ion velocity distribution, and its moments are computed numerically to infer bulk rotation speed and ion temperature. It is found that the time-averaged ion swirl velocity grows to 2 km/s in the near-pole region, and the cathode ions exhibit ion temperatures in the azimuthal direction approaching 8 eV. Both of these quantities exceed the speeds and temperatures anticipated from classical acceleration and heating. Time-resolved laser-induced fluorescence is then employed to investigate the role of plasma fluctuations in driving the time-averaged ion properties. Semicoherent fluctuations at 90 kHz are observed in the ion velocity distribution and its associated moments. These oscillations are correlated with the gradient-driven anti-drift wave, which propagates azimuthally in the near-field cathode plume. Quasilinear theory is used to construct a 1D model for acceleration and heating of the ion population as a result of the anti-drift mode. This approach demonstrates qualitative agreement with the time-averaged ion velocity and temperature, suggesting that the anti-drift mode may be a dominant driver of azimuthal ion acceleration and heating in front of the cathode keeper and the inner half of the inner front pole cover. These results are discussed in terms of their relevance to the erosion of thruster surfaces in the near-field cathode plume. [ABSTRACT FROM AUTHOR]

During a space mission, switching to an electric propulsion system from chemical propulsion, once the spacecraft is out of the Earth's gravity, significantly reduces the mission's overall cost. In electric propulsion, the Hall thruster and gridded ion thruster are established technologies. These thrusters compromise mission longevity due to continuous erosion of the device electrode material. To overcome this issue, an electrode less expanding magnetic field plasma thruster or helicon plasma thruster (HPT), was proposed and research is on going worldwide. The HPT shows scaling of thrust with input power while Hall thrusters and ion thrusters do not. Typically, an inert xenon gas is used as a fuel in HPT devices due to a low ionization potential and non-hazardous nature. Xenon is not easily available in nature and during a space mission it needs to be stored in high pressure tanks. Recently, iodine has been proposed as an alternate to xenon as it is easily available and does not have any storage issues. In most of the numerical simulations, argon is used as a fuel gas to reduce the simulation cost. Using a 1D3V particle-in-cell Monte Carlo collision code, we present here a net thrust generation for different fuel gases such as argon, xenon and iodine. We compare plasma flow rates and directed ion beam velocity for different fuel gases having identical inputs. Thrust and plasma flow are investigated for different magnetic field gradients in the plasma expansion region for unidirectional and bidirectional HPT and is reported here. Using iodine fuel, a significant increase in net thrust is obtained for higher magnetic field divergence for identical simulation input parameters while comparing with xenon fueled cases. [ABSTRACT FROM AUTHOR]

The scaling methodology described in this paper to find the geometry and working parameters of Hall Thrusters is based on algorithms of supervised Machine Learning. The approach considers the determination of the geometrical sizes, propellant mass flow rate and discharge voltage taking thrust and specific impulse as requirements. The magnetic field is also considered. The Gradient Boosting Regression is found as the most suitable algorithm for our purpose. Scaling relies on a specific database of 54 thrusters for the determination of all parameters. The database includes measurements carried out with xenon, krypton and argon as propellant. A unique analytical approach based on the GBR algorithm has been developed and validated to determine the suitable design for a Hall thruster according to space mission requirements. [ABSTRACT FROM AUTHOR]

Electrostatic–magnetic hybrid ion acceleration has been researched to realize high-thrust density and efficient thrust operations. In this study, a newly designed stagnant ring (SR) was installed in an electrostatic–magnetic hybrid thruster with the nominal anode inner radius of 40 mm to improve the thrust performance, and the effects of SR on the thruster operation of xenon propellant were analyzed. During constant-discharge-voltage operations, the discharge current increased with both electrically conductive (copper) and non-conductive (ceramic) SR materials, yet the thrust increased only with the copper SR, which was equipotential to the anode. At lower values of the radial width (H) of the copper SR, the thrust and discharge current were almost dominated by the propellant flow rate from the anode surface. However, the contribution of the propellant flow rate from the cathode tip on the thrust and discharge current became significant when H ≥ 9 mm. The thrust coefficient in electromagnetic acceleration form exhibited a maximum value at H = 9 mm, whereas that in electrostatic acceleration form monotonically increased when H ranged from 0 to 20 mm. The highest thrust efficiency was obtained at H = 12 mm. The study findings indicate that installing a conductive SR can effectively enhance the thrust performance in electrostatic–magnetic hybrid thrusters. • A stagnant ring was installed in an electrostatic–magnetic hybrid thruster. • Thrust performance was deteriorated with electrically non-conductive stagnant ring. • Thrust performance was improved with electrically conductive stagnant ring. • Propellant from the hollow cathode was utilized for thrust generation. [ABSTRACT FROM AUTHOR]

The increasing interest in all-electric, low-Earth orbit satellite constellations has stimulated the rapid development of electric propulsion technology, particularly low-power Hall thrusters. In this study, the difficulties in magnetic field design were analyzed in low-power Hall thrusters, and a new and efficient hybrid production technique is proposed. Hybrid production combines the advantages of coil and permanent magnet production; the main magnetic field is generated by permanent magnets, and the regulating magnetic field is generated by coils in parallel. Accordingly, a prototype of a 600-W hybrid-produced magnetic field Hall thruster, HPHT-600, was designed and tested. The HPHT-600 has a small size (channel outer diameter 54 mm), light weight (1.2 kg), low area–volume ratio (0.148), and low magnetic power. In addition, it exhibits a power envelope of 300–1000 W and a total efficiency of 53.5 % at the discharge voltage of 300 V, anode volume flow rate of 35 sccm, and total specific impulse of 1900 s at 500 V and 20 sccm. • A hybrid-produced magnetic-field hall thruster, combining the advantages of coil and permanent magnet production, is proposed. • The hybrid-produced magnetic-field thruster has great advantages in size and weight. • The performance of the hybrid-produced magnetic-field thruster reaches the level of the state of art Hall thrusters. [ABSTRACT FROM AUTHOR]

Iodine has proven to be a promising alternative to xenon as a propellant for Hall and ion thrusters. High atomic mass and favourable ionization characteristics, comparable to xenon in terms of propulsive performance, together with lower cost compared to xenon makes it an attractive option. However, its reactivity and corrosive nature raise concerns. Tests to assess material compatibility and determine whether thruster components are susceptible to corrosion are unavoidable for its safe adoption as a propellant. This paper describes the main results of an experimental campaign aimed at a qualitative assessment of the compatibility with iodine of different materials. The study included more than fifteen materials that find application in electric propulsion devices, such as cathodes, thrusters and feeding systems, including ceramics such as LaB 6 , polymers, iron and aluminum alloys, and graphite. The specimens were exposed to iodine vapor environments at temperatures reaching approximately 200 °C for extended periods (from three to over 30 h) or were directly exposed to liquid iodine. The experimental setup and results of morphological and elementary analyses are presented and discussed. The research provides some insights into the viability of using iodine as a propellant and the potential challenges associated with its corrosive properties. [ABSTRACT FROM AUTHOR]

This paper proposes increasing the width of the discharge channel to improve the specific impulse of Hall thrusters. In our study, we significantly increased the achievable channel width by optimizing the magnetic circuit topology, and the design freedom of the Hall thruster was improved. A prototype of a wide-channel high-specific-impulse Hall thruster was designed and experimentally verified. The effects of channel width on the discharge process and the characteristics of an aft-loaded magnetic field Hall thruster were investigated. The high-intensity luminous region did not diffuse radially with an increase in the channel width, and the plasma was always concentrated near the channel centerline. A wider channel is more conducive for improving the propellant utilization efficiency, thereby effectively improving the specific impulse of the Hall thruster. By optimizing the discharge channel width, the upper limit of the discharge voltage was increased, and the maximum specific impulse was increased from 3170 to 3794 s, a relative improvement of 20%. The effect of the specific impulse improvement at the same discharge voltage was analyzed and discussed. The results of this study are significant for the design of high-specific-impulse Hall thrusters. [ABSTRACT FROM AUTHOR]

Electric propulsion has become the favored approach for Low Earth Orbit (LEO) maneuvers, resulting in substantial expansion in its use in the satellite industry. The Hall effect thruster's (HETs) high specific impulse and thrust-to-power ratio allow for a wide range of in-space propulsion applications, making it a viable alternative for various space missions. In the space sector, the mass production of HET is currently underway to fulfil the needs of the satellite industry for performing various maneuvers such as orbit boosting, station keeping, deorbitation, collision avoidance, and inter-orbital transfers. The increase in mass production has caused engineering challenges in manufacturing, necessitating an efficient batch production process to guarantee flight qualification within acceptable limits. Engineering production problems may cause manufacturing defects in HET components, leading to non-uniform magnetic field. The non- uniformities in the magnetic field can be observed azimuthally in the channel in various conditions resulting from electrical shorting and geometrical constraints. It is essential to comprehend the effect of such non-uniformities in the magnetic field on the performance of Hall-effect thrusters. An approach to understanding the potential effect of non-uniform magnetic field in HET is by analyzing the efficacy of non-conventional HETs possessing non-uniform magnetic fields. The article comprehensively reviews several non-conventional HETs with distinct channel cross-section geometries, such as linear, racetrack, and wall-less configurations. The paper presents a comparative analysis between non-conventional HETs and conventional HETs operating in low to mid-power configurations for performance evaluation. The review provides discussion of the effects of non-uniform magnetic field on the reduction of optimized HET operation by the presence of heightened erosion and reduction in stability. The review study highlights the importance of optimizing magnetic field topology for developing future thruster designs with enhanced performance and utilization. [ABSTRACT FROM AUTHOR]

This work represents a first attempt to include the complex variety of electron- molecule processes in a full kinetic particle-in-cell/test particle Monte Carlo model for the plasma and neutral gas phase in a Hall thruster. Particular emphasis has been placed on Earth's atmosphere species for the air- breathing concept. The coupling between the plasma and the gas phase is self-consistently captured by assuming the cold gas approximation and considering gas-wall and gas recycling from the walls due to ion neutralization. The results showed that, with air molecular propellants, all the most relevant thruster performance figures degraded relative to the nominal case using Xe propellant. The main reasons can be ascribed to a reduced ionization cross-section, a larger gas ionization mean free path due to lighter mass air species, and additional electron collisional power losses. While vibrational excitations power losses are negligible, dissociation and electronic excitations compete with the ionization channel. In addition, for molecular oxygen, the large dissociation leads to even faster atoms, further reducing their transit time inside the discharge channel. Future studies are needed to investigate the role of non-equilibrium vibrational kinetics and metastable states for stepwise ionization. [ABSTRACT FROM AUTHOR]

Hall thrusters are electric propulsion devices that are widely used in modern spaceflight. To obtain the critical corrosion data effectively and accurately during long-life tests of Hall thrusters, this paper proposes an automated corrosion measurement method based on three-dimensional point cloud technology. This method uses binocular structured light scanning method to obtain surface point cloud data. The point cloud topology relationship of these disordered data is also established by KD-tree and radius filtering. The base plane is determined according to the average of the outer circle plane in the discharge chamber, and the original point cloud data is sliced transversely and longitudinally. The point cloud of section data is extracted and the corrosion width data is obtained according to the round hole feature extraction and center of circle calculation. The corrosion angle is calculated according to the angle between the straight line and the normal of the section. The proposed method has been verified and the results show that the overall error accuracy is within 60 μm, which meets the requirements for automatic measurement of Hall thruster corrosion. It is a real and effective method to obtain the critical corrosion data during long-life tests of Hall thrusters. [ABSTRACT FROM AUTHOR]

This study presents the first experimental demonstration of a Hall Effect Thruster operating with water electrolysis-derived constituents: oxygen for the anode (thruster) and hydrogen for the cathode, both from pressurised bottles. In contrast to prior research where the thruster was operated with oxygen to the anode and xenon/krypton to the cathode, this investigation uses an advanced set-up that safely allowed the combined use of pressurised oxygen and hydrogen. Firstly, a comparative assessment between the established plasma filament cathode (utilised in previous research) and a novel L a B 6 cathode (referred to as Hydrocat), both krypton-fuelled, is conducted. Results show a different IV curve for these cathodes, but negligible disparities in thruster performance for fixed discharge power and anode mass flow. Thrust, anode specific impulse, thrust-to-power ratio, and both, anode and total efficiency of the system using oxygen (anode) and hydrogen (cathode) are then presented and compared against oxygen (anode) and krypton (cathode). The cathode successfully operated on hydrogen, with a reduction in thrust performance of under 10% compared to when krypton is used as the cathode propellant. This performance difference can be attributed to different factors, such as the reduced efficiency of the cathode running with hydrogen due to a higher ionisation potential and the cathode propellant's contribution to thrust, more significant when using heavier propellants such as xenon/krypton compared to hydrogen. The impact of changing the hydrogen-to-oxygen ratio is also assessed and shown to have no impact on the thruster's performance. The most optimal performance was obtained at the highest discharge power tested ( P d = 1953 ± 1 W), using a hydrogen:oxygen ratio of Φ = 1:25. This operating point corresponded to a thrust of 20. 9 ± 0. 2 mN, anode specific impulse of 2130 ± 20 s, thrust-to-power ratio of 10. 7 ± 0. 5 mN/kW, anode thrust efficiency of 11. 2 ± 0. 3 %, and total efficiency of 10. 1 ± 0. 3 %. • First demonstration of a Water Electrolysis fuelled Hall Effect Thruster. • Performance comparison between a krypton-fuelled and a hydrogen-fuelled cathode. • Thrust, specific impulse, anode efficiency and total efficiency metrics. • Influence of the water electrolysis stoichiometric ratio on the performance. • Oxidation studies when using oxygen and hydrogen plasmas. [ABSTRACT FROM AUTHOR]

10.1063/5.0074412 26 P. Guerrero, I. G. Mikellides, J. E. Polk, R. Carmina Monreal, and D. I. Meiron, "Critical implications of ion-surface energy accommodation and neutralization mechanism in hollow cathode physics", J. Appl. Phys. 10.1063/5.0062555 46 L. Condeet al., "Physics of the high specific impulse alternative low power hybrid ion engine (alphie): Direct thrust measurements and plasma plume kinetics", J. Appl. Phys. 10.1063/5.0062607 22 H. Kim, S. Lee, G. Doh, D. Lee, and W. Choe, "Magnetic field tailoring effects on ion beam properties in cylindrical Hall thrusters", J. Appl. Phys. Electric propulsion (EP)[[1]] is a technology widely employed for maneuvering spacecraft on orbit. [Extracted from the article]

Low-frequency axial oscillations in the range of 5–50 kHz stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large-scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insight into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasi-neutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. The predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behavior and the other one, where the low-frequency oscillations coexist with high-frequency oscillations in the range of 100–200 kHz, with the characteristic time scale of the ion channel fly-by time, 100–200 kHz. The other test case demonstrates the effect of a finite temperature of injected neutral atoms, which has a substantial suppression effect on the oscillation amplitude. [ABSTRACT FROM AUTHOR]

More and more CubeSats are being launched. On these small platforms, subsystems such as propulsion and communication ones have to coexist. This article focuses on electromagnetic interaction between these two critical subsystems. Hence, a numerical multi-physics method is proposed in order to quantify perturbation caused by an electric thruster's plume on the antenna of a CubeSat type spacecraft. A plume simulation model has been coupled with electromagnetic simulation software. As an example, the farfield radiation patterns and radioelectric characteristics of a 436 MHz dipole are presented when located near a Hall thruster's plume on a 6U type platform. Changes in radiation patterns are observed in the presence of plume for the dipole antenna. This versatile method makes it possible to represent microwave propagation through a plume for various antennas, thruster's plumes, or relative positions. [ABSTRACT FROM AUTHOR]

The advent of high-power Hall thrusters and the increasing interest toward their use as a primary propulsion system for various missions have given a new boost to the efforts aiming at self-consistent predictive modeling of this thruster technology. In this article, we present a novel approach, which allows enhancing the predictive capability of one-dimensional particle-in-cell (PIC) simulations to self-consistently capture the wave-induced electron transport due to the azimuthal instabilities in Hall thrusters. The so-called "pseudo-2D" PIC scheme resulting from this approach is extensively tested in several operating conditions. The results are compared against a well-established 2D3V axial–azimuthal reference case in terms of the axial profiles of the time-averaged plasma properties, the azimuthal electric field fluctuations and their dispersion features, and the contributions of the force terms in the electron azimuthal momentum equation to the cross-field mobility. We have demonstrated that the pseudo-2D PIC provides a prediction of the above aspects that compares very closely in almost all conditions with those from the full-2D simulation. In addition, the sensitivity of the pseudo-2D simulation results to the numerical parameters associated with our approach is assessed in detail. The outcomes of these analyses have casted light on the next steps to further improve the approach. [ABSTRACT FROM AUTHOR]