Investigation of short-channel design on performance optimization effect of Hall thruster with large height–radius ratio

In this study, the neutral gas distribution and steady-state discharge under different discharge channel lengths were studied via numerical simulations. The results show that the channel with a length of 22 mm has the advantage of comprehensive discharge performance. At this time, the magnetic field intensity at the anode surface is 10% of the peak magnetic field intensity. Further analysis shows that the high-gas-density zone moves outward due to the shortening of the channel length, which optimizes the matching between the gas flow field and the magnetic field, and thus increases the ionization rate. The outward movement of the main ionization zone also reduces the ion loss on the wall surface. Thus, the propellant utilization efficiency can reach a maximum of 96.8%. Moreover, the plasma potential in the main ionization zone will decrease with the shortening of the channel. The excessively short-channel will greatly reduce the voltage utilization efficiency. The thrust is reduced to a minimum of 46.1 mN. Meanwhile, because the anode surface is excessively close to the main ionization zone, the discharge reliability is also difficult to guarantee. It was proved that the performance of Hall thrusters can be optimized by shortening the discharge channel appropriately, and the specific design scheme of short-channel of HEP-1350PM was defined, which serves as a reference for the optimization design of Hall thruster with large height–radius ratio. The short-channel design also helps to reduce the thruster axial dimension, further consolidating the advantages of lightweight and large thrust-to-weight ratio of the Hall thruster with large height–radius ratio.     

Particle-in-cell simulation for effect of anode temperature on discharge characteristics of a Hall effect thruster

Propellant gas flow has an important impact on the ionization and acceleration process of Hall effect thrusters (HETs). In this paper, a particle-in-cell numerical method is used to study the effect of the anode temperature, i.e., the flow speed of the propellant gas, on the discharge characteristics of a HET. The simulation results show that, no matter the magnitude of the discharge voltage, the calculated variation trends of performance parameters with the anode temperature are in good agreement with the experimental ones presented in the literature. Further mechanism analysis indicates that the magnitude of the electron temperature is responsible for the two opposing variation laws found under different discharge voltages. When the discharge voltage is low, the electron temperature is low, and so is the intensity of the propellant ionization; the variation of the thruster performance with the anode temperature is thereby determined by the variation of the neutral density that affects the propellant utilization efficiency. When the discharge voltage is high, the electron temperature is large enough to guarantee a high degree of the propellant utilization no matter the magnitude of the anode temperature. The change of the thruster performance with the anode temperature is thus dominated by the change of the electron temperature and consequently the electron-neutral collisions as well as the electron cross-field mobility that affect the current utilization efficiency.     

Study on the influences of ionization region material arrangement on Hall thruster channel discharge characteristics

There exists strong interaction between the plasma and channel wall in the Hall thruster,which greatly affects the discharge performance of the thruster.In this paper,a two-dimensional physical model is established based on the actual size of an Aton P70 Hall thruster discharge channel.The particle-in-cell simulation method is applied to study the influences of segmented low emissive graphite electrode biased with anode voltage on the discharge characteristics of the Hall thruster channel.The influences of segmented electrode placed at the ionization region on electric potential,ion number density,electron temperature,ionization rate,discharge current and specific impulse are discussed.The results show that,when segmented electrode is placed at the ionization region,the axial length of the acceleration region is shortened,the equipotential lines tend to be vertical with wall at the acceleration region,thus radial velocity of ions is reduced along with the wall corrosion.The axial position of the maximal electron temperature moves towards the exit with the expansion of ionization region.Furthermore,the electron-wall collision frequency and ionization rate also increase,the discharge current decreases and the specific impulse of the Hall thruster is slightly enhanced.     

Investigation of the self-induced magneticfield characteristics in a pulsed plasma thruster with flared electrodes

The self-induced magnetic field in a pulsed plasma thruster(PPT)with flared electrodes is investigated for a better understanding of the working process and the structural design of the thruster.A two-dimensional model of the magnetic field is built and is validated by comparing the simulated results with the experimental results in literature.The magnetic flux density in the discharge channel during the working process is presented and analyzed regarding the electrode structures.The calculated magnetic field flux density decreases from 0.8 T at the upstream to 0.1 T and below at the downstream in the discharge channel(68 J).The peak of the magnetic flux density over time lags behind the current peak,which provides evidence for the existence of a moving plasma sheet in the discharge process.The magnetic field induced by the current in the extra bending part of the anode enhances the Lorentz force,which acts on the charged particles near the propellant.Finally,the geometric study indicates that the electromagnetic impulse bit does not monotonically increase with the flared angle of the electrodes.Instead,it reaches a maximum at a certain flared angle,which could provide significant suggestions for structural optimization.     

Effect of low-frequency oscillation on performance of Hall thrusters

In this paper,a direct connection between the discharge current amplitude and the thruster performance is established by varying solely the capacitance of the filter unit of the Hall thrusters.To be precise,the variation characteristics of ion current,propellant utilization efficiency,and divergence angle of plume at different low-frequency oscillation amplitudes are measured.The findings demonstrate that in the case of the propellant in the discharge channel just meets or falls below the full ionization condition,the increase of low-frequency oscillation amplitude can significantly enhance the ionization degree of the neutral gas in the channel and increase the thrust and anode efficiency of thruster.On the contrary,the increase in the amplitude of low-frequency oscillation will lead to increase the loss of plume divergence,therefore the thrust and anode efficiency of thruster decrease.     

Experimental and numerical simulation study of the effect for the anode positions on the discharge characteristics of 300 W class low power Hall thrusters

Low-power Hall thruster(LHT) generally has poor discharge efficiency characteristics due to the large surface-to-volume ratio.Aiming to further refine and improve the performance of 300 W class LHT in terms of thrust and efficiency,and to obtain the most optimal operating point,the experimental study of the discharge characteristics for three different anode positions was conducted under the operation of various discharge voltages(100-400 V) and anode mass flow rates(0.65 mg·s^-1 and 0...     

Simulation of the effect of a magnetically insulated anode on a low-power cylindrical Hall thruster

The intersection point of the characteristic magnetic field line (CMFL) crossing the anode boundary with the discharge channel wall,and its influence on thruster performance and the energy and flux of ions bombarding the channel wall,have been studied numerically.The simulation results demonstrate that with the increase in distance from the crossover point of the CMFL with the channel wall to the bottom of the thruster channel,the ionization rate in the discharge channel gradually increases;meanwhile,the ion energy and ion current density bombarding the channel wall decreases.When the point of the CMFL with the channel wall is at the channel outlet,the thrust,specific impulse,and efficiency are at a maximum,while the ion energy and ion current density bombarding the channel wall are at a minimum.Therefore,to improve the performance and lifetime of the thruster,it is important to control the point of intersection of the CMFL with the channel wall.     

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.     

Simulation study on the influence of magnetic field in the near-anode region on anode power deposition of ATON-type Hall thruster

The highest deposition of power and temperature is always near the cusp of the ATON-type Hall thruster. This shows that when there are electrons gathering at the cusp, the distribution of heat load will be uniform, which will potentially damage the reliability. Therefore, we optimize the magnetic field near the anode. We changed the magnetic field characteristics in the near-anode region with an additional magnetic screen, and performed numerical simulation with particle-incell simulation. The simulation results show that the magnetic field of the thruster with the additional magnetic screen can alleviate the over-concentration of power deposition on the anode and reduce the power deposition in the anode by 20%, while ensuring that the overall magnetic field characteristics do not change significantly.     

Performance of a 4 cm iodine-fueled radio frequency ion thruster

The performance of an iodine radio ion thruster with a 4 cm diameter(IRIT4) was studied experimentally in this paper. Regulation of the mass flow rates of the iodine propellant is achieved by using a temperature control method of the iodine reservoir. Performance of the thruster using iodine as propellants is obtained at different total thruster powers of 40.6–128.8 W,different grid voltages of 1000–1800 V and the iodine flow rate of 100 μgs~(-1). Results show that thrust and specific impulse increase approximately linearly with the increasing total thruster power and the screen grid voltage. The thrust of 2.32 mN and the specific impulse of 2361 s are obtained at the nominal total thruster power of 95.8 W and the screen grid voltage of 1800 V. It is also indicated that performance of the iodine propellant is comparable to that of the xenon propellant; and a difference between them is that the iodine thrust is slightly higher than xenon when the total thruster power is more than 62 W. At the nominal 95.8 W total thruster power, the thrust values of them are 2.32 m N and 2.15 mN respectively, and the thrust-to-power ratios of them are 24.2 mN kW~(-1) and 23.5 mN kW~(-1), respectively.     

Effect of the Discharge Voltage on the Performance of the Hall Thruster

In this paper,a two-dimensional physical model is established according to the discharging process in the Hall thruster discharge channel using the particle-in-cell method.The influences of discharge voltage on the distributions of potential,ion radial flow,and discharge current are investigated in a fixed magnetic field configuration.It is found that,with the increase of discharge voltage,especially during 250-650 V,the ion radial flow and the collision frequency between ions and the wall are decreased,but the discharge current is increased.The electron temperature saturation is observed between 400-450 V and the maximal value decreases during this region.When the discharge voltage reaches 700 V,the potential distribution in the axis direction expands to the anode significantly,the ionization region becomes close to the anode,and the acceleration region grows longer.Besides,ion radial flow and the collision frequency between ions and the wall are also increased when the discharge voltage exceeds 650 V.     

Simulation study of the influence of leak electrons on the discharge characteristics of a cusped field thruster

Previous studies have shown that leak electrons in cusped field thrusters can move along the channel axis to the anode after crossing the magnetic cusp on the exit. In this paper, a one- dimensional fluid model is built along two typical electron paths to study the influence of leak electrons on the discharge characteristics of a cusped field thruster, considering the electron temperature equation. It is found that the frequencies of low-frequency oscillations increase with a decrease in the proportion of leak electrons, which is related to an increase in the ion speed in the channel. Simulation results show that the position of the peak electron temperature is near the magnetic cusp on the exit and the position of the peak electron density is located downstream from the middle magnetic tip. With a decrease in the proportion of the leak electrons, the peak electron temperature and peak electron density decrease and the position of the peak electron density moves away from the exit, which is related to a decrease in the potential fall on the exit and an increase in confinement of electrons to the middle magnetic cusp.     

Investigation on plasma characteristics in a laser ablation pulsed plasma thruster by optical emission spectroscopy

In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion, a novel laser ablation pulsed plasma thruster is proposed, which separated the laser ablation and electromagnetic acceleration. Optical emission spectroscopy is utilized to investigate the plasma characteristics in the thruster. The spectral lines at different times,positions and discharge intensities are experimentally recorded, and the plasma characteristics in the discharge channel are concluded through analyzing the variation of spectral lines. With the discharge energy of 24 J, laser energy of 0.6 J and the use of aluminum propellant, the specific impulse and thrust efficiency reach 6808 s and 70.6%, respectively.     

A SMALL UNBALANCED MAGNETRON SPUTTERING SOURCE WITH MULTIPOLE MAGNETIC FIELD ANODE

A small unbalanced magnetron atom source with multipole cusp magnetic field anode is described.The co-axial magnetron rpinciple is extended to the circular planar magnetron atom source,which raises the efficiency of sputtering target area up to 60%.The multipole magnetic field is put in the anode.which makes the unbalanced magnetron atom source run in a higher discharge current at a lower arc voltage condition.Meanwhile.the sputtering atoms through out the anode can be ionized partially,because the electron reaching the anode have to suffer multiple collisons in order to advance across the multipole magnetic field lines in the anode,which enhances the chemical reactivity of the ejecting atoms in film growth and improve the property of film depositing.     

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages. To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition, a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages. The results show that when the discharge voltage is high, the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition; with the gradual strengthening of the ignition process, the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases. The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.     

Magnet stage optimization of 5 kW multi-cusped field thruster

The multi-cusped field thruster is a unique electric thruster device, which has many advantages such as long lifetime, large-range thrust throttling ability, high thrust density, and low mass. The thruster employs several alternating polarity permanent magnets to create a periodic magnetic field with several cusps. Previous studies have indicated that the basic ionization and acceleration processes are directly related to the electron motion behavior, which mainly depends on the magnetic field characteristics. The magnet number and magnet stage length are two key magnetic field parameters that have important effects on the thruster performances. In this paper, both the magnet number and magnet stage length parameters are studied for the optimization of a 5 k W multi-cusped field thruster. The results indicate that the three-stage thruster has a better electron confinement than the two-stage thruster. It has lower ion energy loss at the wall, and shows a higher ionization rate. Therefore, the three-stage magnetic field is a superior magnetic field configuration. Besides, the three-stage magnetic field simulation results indicate that an optimal accelerating electric field distribution and ionization region distribution could be obtained when the magnet length ratio is 78:25:20.     

Life test research of a high specific impulse Hall thruster HEP-140MF

In this study, a high specific impulse Hall thruster, HEP-140MF, having a high discharge voltage, was used to accelerate ions. We aimed to obtain a high specific impulse and an acceleration zone moving downstream toward the channel exit to reduce wall sputtering erosion of the walls of the discharge channel, hence ensuring an enhanced lifetime. To study the lifetime characteristics of the high specific impulse Hall thruster, a life test was performed on the HEP- 140MF thruster for the first time, and performance parameters, such as thrust, specific impulse, and efficiency, were measured. Changes in the performance parameters and evolutions in the surface profiles of the discharge channel wall were summarized. The reasons contributing to these changes during the life test were analyzed. Moreover, the accelerated life test method was validated on the HEP-140MF.     

Application and development of the pulsed plasma thruster

The application and development of pulsed plasma thrusters(PPTs) in recent years are reviewed in this paper. The advantages of PPTs are discussed. The schematics, propulsion performance parameters and key physical processes of PPTs are described. Some representative PPT products and flight systems developed in recent years are presented to show the performance of the PPT.Studies about how electrode structures, discharge circuits, propellant materials, energy discharge method, propellant feed method, ignition method and number of thruster heads influence the PPT performance are presented and analyzed. The ignitor design method, ignition process and propellant carbonization are introduced to discuss the reliability and lifetime issues in PPTs. The modeling methods of the discharge circuit, as well as ablation, ionization and acceleration in PPTs are presented. Finally, the application of PPTs in the future is analyzed and some suggestions for PPT development are proposed.     

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 $x$ 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 a helicon plasma source in a magnetoplasma rocket engine

The helicon plasma source, which generates high thrust and high impulse, is of vital importance for magnetoplasma rocket engines. In this work, a multi-component, two-dimensional, axisymmetric fluid model coupled with an electromagnetic field was developed to model the helicon discharge. The simulation results demonstrate that: (i) the discharge mode changes twice—each conversion is accompanied by a plasma density jump and an electron temperature peak in the discharge; (ii) when the input current increases, the plasma density increases, and ionization occurs faster; (iii) the background magnetic field clearly enhances the discharge; (iv) the plasma density may be smaller if the discharge has not entered the wave mode.