Hall Thruster Research Articles

Studies of growing waves in Hall thruster beam plasma under the influence of electron temperature

Studies of growing waves in Hall thruster beam plasma under the influence of electron temperature

Simultaneous experimental verification of indirect thrust measurement method based on Hall-effect thruster and plasma plume

In this work, the experimental verification of the indirect thrust measurement method based on the plume of a low power Hall-effect thruster and its effect on the thruster is investigated. The Hall-effect thruster with permanent magnets was exhibited and the performance parameters and the plume parameters were introduced, and the thrust of the thruster was measured simultaneously using both direct and indirect measurement methods, which validate the effect due to thruster and the measurement devices. The experimental verification of the thrust amendment values was proposed considering the ion flux collection, the neutral atoms, and the additional momentum due to ion reflecting, and the corresponding amended thrust results were exhibited separately which show the contribution of each factor, and the modification method could provide reliable results for indirect thrust measurement.

14-moment maximum-entropy modeling of collisionless ions for Hall thruster discharges

Ions in Hall effect thrusters are often characterized by a low collisionality. In the presence of acceleration fields and azimuthal electric field waves, this results in strong deviations from thermodynamic equilibrium, introducing kinetic effects. This work investigates the application of the 14-moment maximum-entropy model to this problem. This method consists in a set of 14 partial differential equations (PDEs) for the density, momentum, pressure tensor components, heat flux vector, and fourth-order moment associated with the particle velocity distribution function. The model is applied to the study of collisionless ion dynamics in a Hall thruster-like configuration, and its accuracy is assessed against different models, including the Vlasov kinetic equation. Three test cases are considered: a purely axial acceleration problem, the problem of ion-wave trapping, and finally the evolution of ions in the axial-azimuthal plane. Most of this work considers ions only, and the coupling with electrons is removed by prescribing reasonable values of the electric field. This allows us to obtain a direct comparison among different ion models. However, the possibility to run self-consistent plasma simulations is also briefly discussed, considering quasi-neutral or multi-fluid models. The maximum-entropy system appears to be a robust and accurate option for the considered test cases. The accuracy is improved over the simpler pressureless gas model (cold ions) and the Euler equations for gas dynamics, while the computational cost shows to remain much lower than direct kinetic simulations.

Method for Calculating Thrust Vector Eccentricity Angle of Electric Thruster

The installation of a propulsion device in space missions requires the thrust vector to be in line with the centroid of the satellite platform. If the installation is eccentric, interference torque occurs on the satellite body, which is not conducive for the attitude control of the whole satellite. In this paper, a method for calculating the thrust vector eccentricity angle by Gaussian surface fitting is proposed, which is suitable for a class of electric thrusters, for which the plume is conformed to point source distribution. For the cylindrical-shaped plume that cannot be regarded as a point source, a new weight function is proposed. A Hall thruster is considered an example to experimentally verify the method. Error analysis shows that the calculation accuracy in most of the cases is within 10%. To obtain the result of a small error, a preprocessing procedure is proposed before applying the method for optimization. Moreover, considering the contribution of the ion energy distributed along the angle, the calculation method is corrected and improved; and it is found that the thrust vector eccentricity angle of the Hall thruster is overestimated by about 20–30% when the angular distribution of the ion energy is not considered.

On Scaling of Hall-Effect Thrusters Using Neural Nets

Hall-effect thrusters (HETs) are widely used for modern near-Earth spacecraft propulsion and are vital for future deep-space missions. Methods of modeling HETs are developing rapidly. However, such methods are not yet precise enough and cannot reliably predict the parameters of a newly designed thruster, mostly due to the enormous computational cost of a HET plasma simulation. Another approach is to use scaling techniques based on available experimental data. This paper proposes an approach for scaling HETs using neural networks and other modern machine learning methods. The new scaling model was built with information from an extensive database of HET parameters collected from published papers. Predictions of the new scaling model are valid for the operating parameters domain covered by the database. During the design, this model can help HET developers estimate the performance of a newly designed thruster. At the stage of experimental research, the model can be used to compare the achieved characteristics of the studied thruster with the level obtained by other developers. A comparison with the state-of-the-art HET scaling model is also presented.

VENμS: Mission Characteristics, Final Evaluation of the First Phase and Data Production

VENμS (Vegetation and Environment New micro (μ) Satellite) is a micro satellite launched in 2017 by the Israeli Space Agency (ISA) and the French Centre National d’Etudes Spatiales (CNES). VENμS is a research satellite containing two very different devices: an electric Hall effect thruster and a multispectral optical camera. This paper focuses on the multispectral camera. The camera provides images at a resolution of 5 m, with a field of view of 27 km, and the orbit of the satellite was chosen to allow us to revisit of each observed site with constant angles every second day. In November 2020, VENμS ended the first phase of its mission. This phase, called VM01, allowed us to provide about 150 accurate time series over selected scientific sites over almost three years. Extensive work was conducted to calibrate the camera and assess the quality of the products. Not everything worked as planned before launch and a large amount of work was necessary to correct some defects of the camera or to improve the geometric registration of images. This article establishes the image quality VM01 final assessment including the presentation of radiometric and geometric calibration methods, the estimation of instrument performances and their associated temporal stabilities and the monitoring activities. In addition, it highlights the whole mechanism of data programming, reception and production. The end of VM01 phase is not the end of the VENμS mission, and a new phase started on a one-day repeat orbit.

Broadband (kHz–GHz) characterization of instabilities in Hall thruster inside a metallic vacuum chamber

Hall thrusters are known to exhibit a large variety of instabilities. Their physical mechanisms have been identified at low (kHz) and intermediate (MHz) frequencies, even though they are still not fully understood. Furthermore, electromagnetic radiations generated by Hall thrusters, named “self-emission” of the thruster, have been measured from kHz to MHz as expected from the identified instabilities, but also at higher frequencies. The origin of the high frequency (GHz) self-emission remains for now unknown. Assessing this self-emission, that is important for understanding the physics of Hall thrusters as well as for electromagnetic compatibility issues with the spacecraft, is challenging. Another aspect that makes the understanding of the physics of Hall thrusters complex comes from the eventual coupling between instabilities, which has been recently suggested and observed. The aim of this paper is to explore the possibility of characterizing simultaneously instabilities in Hall thrusters on a broadband frequency range (from kHz to GHz) in situ, meaning in a conventionally used vacuum chamber where Hall thrusters are usually operated. We show in this paper that, despite the reverberant nature of the vacuum metallic chamber, useful information is extracted at low and intermediate frequencies and even at high frequency from the measurements done with an antenna in this environment.

Fluid simulation on effect of background magnetic field on plasma characteristics in a Hall thruster

Herein, the effect of the background magnetic field on plasma characteristics in a Hall thruster is numerically investigated using DUT-HTFS [Li et al., AIP Adv. 12, 015117 (2022)], an integrated fluid simulation platform on Hall thruster plasmas. The research shows that the background magnetic field significantly influences the distribution of the plasma density, especially the radial profiles of the plasma density near the ionization region and the acceleration region. In addition, the positions of the peak values of the electron power absorptions mainly occur near the dielectric walls of the exhaust plane, and the electron power absorption mechanism is mainly dominated by the Ohmic heating. The peak values of the axial electron current density on the inner and outer dielectric walls are higher than that on the centerline. This phenomenon is closely related to the near wall conduction mechanism of the electrons. In addition, the background magnetic field significantly influences the shapes, positions, and magnitudes of the peak values of the plasma parameters, such as the plasma density, the electron current density, the axial electric field, the electric potential, and the ionization rate. These results will help us to provide a valuable reference and reduce the risk for the experimental test programs and the applications of Hall thrusters in the future.

Plasma diagnosis of an unclosed E × B drift thruster with a visible ionization zone

The traditional annular closed-loop E × B drifting Hall thruster is limited by its compact structure. Two-dimensional (2D) distribution of the plasma parameters inside the discharge channel cannot be accurately measured, thus directly hindering further understanding of the discharge process. In this paper, we propose to employ an unclosed E × B drift thruster with a visible (UDTv) ionization zone to conduct research into the effects of the crossed electric field and magnetic field on the plasma distribution inside the discharge channel. Experiments showed that the UDTv presented discharge similar to a Hall thruster, especially the low-frequency oscillation related to the discharge voltage. A 2D symmetrically crescent-shaped distribution of plasma inside the channel with a hollow zone located near the maximum of the magnetic field was clearly captured by optical imaging and an emission spectrometer. Correlation between the location of the maximal magnetic gradient and the 2D ionization zone configuration was verified. A decreased magnetic mirror effect at the location of the maximum magnetic field enhanced the electron–wall interaction, inducing near-wall conduction and secondary electron emission. The electron temperature presented a canyon distribution, resulting in a bimodal configuration of the plasma density. Increased flowrate lowered the ionization inside the channel and transformed the plasma distribution into a unimodal structure because of enhanced electron conduction and the lower electron temperature. Generally, the ability to capture the correlation between 2D plasma distribution and the magnetic field inside the discharge channel was successfully demonstrated, thus proposing new ideas for further research into the internal plasma of Hall thrusters.

Atmospheric propellant fed Hall thruster discharges: 0D-hybrid model and experimental results

As part of on-going efforts in advancing air-breathing electric propulsion, the HT5k Hall thruster was characterized in six operating conditions, ranging from 5 mg s−1 to 7 mg s−1 of 0.56N2 + 0.44O2 mass flow rate and 225 V to 300 V of discharge voltage. The cathode was operated with N2 at mass flow rates between 0.5 mg s−1 and 0.7 mg s−1. This paper presents a 0D-hybrid model for atmospheric propellant fed Hall thruster discharges. Verified performance ranged between 30 mN to 120 mN in thrust, 1.2 kW to 5.2 kW in discharge power, and 8% to 18% in anodic efficiency. Calibrated model comparison against experimental data resulted in a mean absolute error of 3.7% in thrust and 7.6% in discharge power.

Development of a high dynamic range retarding potential analyzer for electric propulsion plume diagnosis.

A new high dynamic range retarding potential analyzer design is proposed to measure the ion energy distribution in electric propulsion plasma plumes. The main difference between the proposed probe and previous designs is an ion-optical system with a high negative accelerating potential. Applying the principle of acceleration and focusing of the ion flow provides the correct operation of the probe in a dense plasma in which the Debye length can be ten times smaller than the diameter of the grid apertures. As a result, the new probe has high transparency with an extended operating range of measured plasma densities. Another advantage of the probe is its accurately known and time-stable transparency for ions, so the probe can measure the absolute values of the ion current density like the Faraday probe. The analyzer geometry, which provides measurement in the range of ion current densities up to 100 A/m2 at ion energies up to 2000eV with an error of no more than 2%, was determined using numerical simulation. We present the measurement results of the plasma plume of a Hall effect thruster with a nominal discharge power of 2.3 kW.

Study on the characteristics of non-Maxwellian magnetized sheath in Hall thruster acceleration region

The secondary electron emission (SEE) and inclined magnetic field are typical features at the channel wall of the Hall thruster acceleration region (AR), and the characteristics of the magnetized sheath have a significant effect on the radial potential distribution, ion radial acceleration and wall erosion. In this work, the magnetohydrodynamics model is used to study the characteristics of the magnetized sheath with SEE in the AR of Hall thruster. The electrons are assumed to obey non-extensive distribution, the ions and secondary electrons are magnetized. Based on the Sagdeev potential, the modified Bohm criterion is derived, and the influences of the non-extensive parameter and magnetic field on the AR sheath structure and parameters are discussed. Results show that, with the decrease of the parameter q, the high-energy electron leads to an increase of the potential drop in the sheath, and the sheath thickness expands accordingly, the kinetic energy rises when ions reach the wall, which can aggravate the wall erosion. Increasing the magnetic field inclination angle in the AR of the Hall thruster, the Lorenz force along the direction acting as a resistance decelerating ions becomes larger which can reduce the wall erosion, while the strength of magnetic field in the AR has little effect on Bohm criterion and wall potential. The propellant type also has a certain effect on the values of wall potential, secondary electron number density and sheath thickness.

Simulation of the microwave propagation through the plume of a Hall thruster integrated on small spacecraft

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.

Application of electric thrusters in a spacecraft propulsion system

The place of electric rocket thrusters in a spacecraft propulsion system is pointed out; the tasks for such propulsion system are described. The modern classification of electric thrusters is given, in accordance of that one there are four classes, dissimilar due to a nature of processes that impart a kinetic energy to a propellant: electrothermal, electrostatic, pulsed and magnetoplasmodynamic. In order to illustrate an electric rocket thrusters sate of art, examples different classes electric rocket thrusters for modern spacecrafts are presented; the technical characteristics, such a thrust, specific impulse, powered energy and efficiency are systematized. As a general electric rocket thrusters for spacecraft propulsion system were chosen electrostatic thrusters: stationary plasma (Hall thrusters) and ion thusters. For the different classes of electric rocket thrusters the common characteristics are defined as a set of: specific impulse (that describes thruster propellant efficiency), thrust cost (determines electric power consumption per unit thrust) and propellant type (combines thruster’s technical and economical characteristics). A necessity is stated to take into account the cost parameters of an electric rocket thruster design and a manufacturing during a propulsion system developing for a next generation spacecraft. The tasks are determined for the further research in the area of a techno-economic efficiency of electric rocket thrusters exploiting as a part of a spacecraft’s propulsion system.

Effects of unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio

The large height-radius ratio design of the Hall thruster increases the difference of radial distributions of magnetic field and plasma parameters in the channel, so that the optimal discharge effect of the thruster cannot be guaranteed under the symmetrical magnetic field configuration relative to the channel centerline. In this work, the effects of the unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio were studied through experiments and PIC simulations. The results show that the thruster can realize stable discharge in a wide power range under unsymmetrical magnetic fields. Also, the unsymmetrical magnetic field plays a positive role in improving the discharge performance and prolonging the service life of the thruster. The inward-inclined magnetic field can effectively improve the discharge performance of the thruster, and the discharge efficiency can be increased by 1.5% under the rated working condition compared with the symmetrical magnetic field. The advantage in performance is mainly attributed to the improvement of ionization efficiency of propellant. The outward-inclined magnetic field is more conducive to prolong the service life of the thruster, and the peak value of ion power deposition on the inner wall can be reduced by 40% under the rated working condition due to the outward inclination of the ionization zone and the reduction of the radial electric field. However, under unsymmetrical magnetic field, the ionization zone deviates from the channel center, and the high ionization rate zone is more dispersed in distribution, thus leading to the increase in plume divergence angle. This study verifies that the unsymmetrical magnetic field has certain advantages under the structure of large height-radius ratio, which could be used as a guidance for the optimal design of Hall thruster with large height-radius ratio.

Numerical study of the effect of aft-loaded magnetic field on multiple ionizations in Hall thruster

It is assumed that the shift of a strong magnetic field region with a positive gradient from exit plane to outside, namely the transit from a normal loaded magnetic field to an aft-loaded one, enhances the multiple ionization process in the magnetically shielded Hall thruster. To confirm this conjecture, a comparative study is carried out numerically with a particle-in-cell method. The simulation results prove that compared with the normal loaded magnetic field, the application of aft-loaded magnetic field enhances the multiple ionization process. This study further analyzes the ionization characteristics of the transition from low-charged ions to high-charged ions under two magnetic field conditions and the influence of the magnetic strength of aft-loaded magnetic field on the multiple ionization characteristics. The study described herein is useful for understanding the discharge characteristics of Hall thruster with an aft-loaded magnetic field.

Early experimental investigation of the C12A7 hollow cathode fed on iodine

To fully realize the superiority of the iodine electric propulsion system in streamlining the size and reducing the operating costs, iodine hollow cathode technology must be developed. Considering the corrosiveness of iodine and the possible impurity of the working propellant, the C12A7 hollow cathode with promising chemical ability was developed and tested. The C12A7 hollow cathode with a nominal current of 1–4 A was successfully ignited with iodine from the reservoir outside the vacuum chamber. It was operated at 1 A of anode current with a 1.2 mg s−1 iodine mass flow rate. Despite involuntary extinguishment, the C12A7 hollow cathode could be restarted repeatedly with a single operation time of up to 12 min and a total duration of 30 min . The unexpected fluctuation of iodine flow may be the reason for the short operation time. Experimental results and microscopical observation of the electride emitter show the compatibility of the iodine and electride emitter. For the development and demonstration of future single-iodine electric propulsion of Hall thrusters, the iodine storage and supply system with precise control and regulation may be the critical technology.

The effect of anode axial position on the performance of a miniaturized cylindrical Hall thruster with a cusp-type magnetic field

A 200 W cylindrical Hall thruster with a cusp-type magnetic field was proposed, manifesting convergent plume and high specific impulse. In this paper, a series of ring-shaped anodes are designed and the influence of anode axial position on the performance of CHT with a cusp-type magnetic field is studied. The experimental results indicate that the thruster keeps stable operation at the condition of 140–270 W discharge power. When the anode moves axially towards the upstream cusp field, the thrust enhances from 6.5 mN to 7.6 mN and specific impulse enhances from 1658 s to 1939 s significantly. These improvements of thruster performance should be attributed to the enhancement of current utilization, propellant utilization and acceleration efficiency. According to the analyses on the discharge characteristics, it is revealed that as the anode moves upstream, the electron transport path could be extended, the magnetic field in this extended path could impede electron cross-field transport and facilitate the ionization intensity, yielding to the enhancement of current utilization and propellant utilization efficiency. Moreover, along with this enhancement of upstream ionization at the given anode flow rate, the main ionization region is thought to move upstream and then separate more apparently from the acceleration region, which has been demonstrated by the narrowing of ion energy distribution function shape. This change in acceleration region could decrease the ion energy loss and enhance acceleration efficiency. This work is beneficial for optimizing the electrode structure of thruster and recognize the ionization and acceleration process under the cusp magnetic field.

Force probes for development and testing of different electric propulsion systems

Diagnostics with force probes in plumes of electric propulsion systems for spacecraft (thrusters) are presented. This contribution focuses on showing example measurements with force probes for the most common gridless ion thruster types. The gridless thrusters are investigated at typical operation modes with a force probe at fixed or variable positions in the plume. The probe measures the force on a tiny plate that is attached to a sensitive cantilever in the plume. The elastic deflection of the cantilever is measured interferometrically and translated into a proportional force. Several variants of the instrument have been developed. A HEMP thruster is investigated with a variant of the force probe that simultaneously measures two components of the force vector. With this vectorial probe, it is possible to determine the force vector acting on the probe target while moving the probe through the thruster plume. A Hall thruster is investigated with a simplified variant of the probe, which measures the force along one axis and is equipped with an additional shutter in front of the target. This allows monitoring over long periods of operation. Finally, a force probe is used as an indirect thrust balance for a FEEP thruster. In this case, the force probe can collect the entire plume.

A wavelet-based method for thrust noise assessment in gravitational wave detection over wide-frequency-range

Electric thrusters are considered to be the most promising propulsion system of choice for space gravitational wave detection. However, the requirement of high accuracy and drag-free control results in significant challenges in thrust measurements. In order to detect gravitational wave signals over a wide frequency range, it is necessary to assess the thrust noise of electric thrusters. This paper demonstrates a wavelet-based method for thrust noise evaluation in a time-frequency domain aspect, and aims to expand thrust noise analysis to a wide frequency range from 10−3Hz–1Hz. Over this frequency range, a frequency-varying metric boundary is proposed for thrust noise evaluation. This metric boundary is established based on the spectral density of gravitational waves and the time-varying spectrum analysis method, which is used to judge whether the thruster exceeds the requirements for the detection of gravitational waves. A Hall Thruster was ignited and measured experimentally to verify the thrust noise assessment method. The metric boundary evaluates the thrust noise limits in the frequency range from 10−3 to 1Hz over the entire operating duration to the thruster's power-off period. This time-frequency-varying thrust noise assessment method allows us to identify the time and frequency band within which the electric thruster is capable of exceeding the requirements for gravitational wave detection.