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This study systematically investigated the influence of the position and inclination angle of an externally mounted hollow cathode in 1.35 kW magnetically shielded Hall thrusters to establish the r...

Using a permanent magnet to realize a design with a large height-radius ratio can effectively reduce the radial size of the thruster. The experimental results show that a Hall thruster with a large height-radius ratio also has significant advantages in its discharge performance. Taking the 1.35 kW Hall thruster HEP-1350PM, which has a large height-radius ratio, as an example, the thrust, specific impulse, and efficiency of HEP-1350PM are increased by up to 4.3%, 10.4%, and 7%, respectively, as compared to SPT-100, while its weight is only 56% of that of SPT-100. Numerical simulations were performed to understand the discharge characteristics of a Hall thruster with a large height-radius ratio and the internal mechanism of its performance improvement. The results show that the small middle diameter and wide channel structure concentrate the distribution of the neutral gas in the channel, accelerate the decrease of the propellant density along the axial direction, and move the main ionization zone closer to the channel upstream. These factors increase the ionization concentration, ionization rate peak, working medium utilization rate, and voltage utilization rate. They also reduce the ion loss on the wall surface and plume divergence, thereby improving the comprehensive discharge performance. This study verifies the feasibility of a large height-radius ratio in the design of a Hall thruster, and demonstrates that the design would not only be valuable for reducing the volume and weight of the thruster, but also has the advantages of enhancing its discharge performance and prolonging its working life.

In this study, a 1.35 kW HEP-100X Hall thruster is used to explore effective methods for improving the global efficiency of a Hall thruster across a wide range of flow rates, from the perspective o...

Magnetic pole erosion is a key life-limiting factor of low-power Hall thrusters. In this study, the effects of the magnetic field intensity near the inner magnetic pole on the pole erosion of a 100 W permanent-magnet Hall thruster at rated operating point were investigated using magnetic field intensity adjustment technology. The experimental results indicate that the erosion rate of the inner magnetic pole decreased considerably with a decrease in the magnetic field intensity near the inner magnetic pole, and the erosion rate can be decreased by over 37.5% when the magnetic field intensity decreased by 20%. Further analysis indicates that the decrease of magnetic field intensity reduces the number of electrons moving along the magnetic field lines to the magnetic pole, and increases the surface potential of the magnetic pole. The reduction of the potential difference between the channel outlet and the magnetic pole leads to a decrease in the current density and energy of the ions sputtered to the magnetic pole, which contributes greatly to the decrease in pole erosion rate. This study provides a reference for the protection of magnetic pole erosion.

In this paper, the relationship between the morphology of the cathode crater and plasma ionization between thrusters is studied by adjusting the input energy of the micro-cathode arc thruster (μCAT). We monitor the morphology of the cathode crater of the μCAT using scanning electron microscopy and explore the relationship between the crater morphology and the internal energy loss of the cathode crater. This relationship, combined with the numerical simulation results, is used to monitor the ionization between the electrodes of the μCAT using an enhanced intensified charge coupled device spectrum detector. The effect of cathode crater morphology on the ionization of the propellant during the operation of the μCAT is determined. The results show that with a change in the input power processing unit voltage, the external profile and depth-to-diameter ratio of the cathode crater change, resulting in a change in the internal energy loss of the thruster cathode crater and then affecting the ionization efficiency of the cathode working fluid in the μCAT. Under the condition of basically unchanged cathode feed energy flow density, reasonable adjustment of the depth-to-diameter ratio of the cathode crater can effectively improve the ionization efficiency of the cathode working fluid in the μCAT.

Prior experiments have demonstrated that the pole in a magnetically shielded Hall thruster sputters and erodes visibly, in contrast with that in an unshielded thruster. To determine the reason for this, a particle-in-cell simulation was conducted, and the difference between shielded and unshielded thrusters in terms of plasma behavior near the exit plane was studied. The results show that in the case of the magnetically shielded thruster, the ion flux peak is on the magnetic pole face with higher ion energy, indicating severer erosion at the pole. By contrast, the flux peak of the unshielded thruster is on the head face of the channel wall, indicating severer bombardment at the wall and milder erosion at the pole. Therefore, pole erosion occurs in the magnetically shielded thruster, and channel head face erosion can be observed in the unshielded thruster. In addition, the simulation results indicate that the greater the outward shift of the magnetic field, the severer the pole erosion.

Ionic wind has been widely used in the fields of flow control, heat cooling, thruster, and so on. In this work, an investigation of ionic wind under different magnetic field configurations is processed. By changing the position relationship between the electrode and the magnetic field, the magnetic field configuration in the discharge region is modified. With the injection of different magnetic field configurations to the discharge region, the amplitude of Trichel pulse is decreased, and the pulse frequency is increased. Besides, the ionic wind velocities’ distribution is deflected and the electrical-to-kinetic energy conversion efficiency is enhanced. The mechanism is analyzed by considering the movement path of particles in the ionization region and drift region under different magnetic field configurations. These results illustrate that the magnetic field configuration would be a method to adjust the direction and improve the electrical-to-kinetic energy conversion efficiency of ionic wind. This method provides a feasible way to regulate the performance of ionic wind without additional energy consumption.

In this investigation, to monitor the cathodic ionization process of the microcathodic arc thruster, electrical detection was combined with enhanced ICCD spectroscopic detection to diagnose the cathodic ionization characteristics of microcathode arc thrusters with 1 μs time resolution for examining the microsecond-level discharge process. After we used the titanium ion spectroscopy model to calculate the ion density distribution during the cathode ionization of the microcathode arc thruster, we found that the microcathode arc thruster showed a double peak of titanium ions in one cycle. This phenomenon may be related to the combined effect of arc heat transfer and ion current impact on the cathode during the discharge of the microcathode arc thruster. The results showed that changes in the input energy of the power processing unit can effectively affect the temporal relationship between arc power peak and arc current peak, which in turn affects the ionization of the cathode of the microcathode arc thruster.

A decoupling method is proposed for micro-Newton thrust measurement with a torsion pendulum. The basic approach is to reduce the influences introduced by the propellant tube and wires of the thruster. A hollow aluminum tube is used to hang the torsion pendulum and is also chosen as the transport pipe for the propellant of the thruster. The electric control box of the thruster is mounted on the pendulum body, which is powered by an externally installed power supply through a liquid metal conductive unit. The control of the electric control box is performed through wireless transmission. With this design, the influences of the propellant tube and connection wires between the torsion pendulum and the outside device are reduced and the stability of the torsion spring constant of the system can be improved. The use of the liquid metal conductive unit reduces the coupling between the wires and the measurement system. The feasibility of the wireless transmission is analyzed. The error sources during the thrust measurement are analyzed, and the expected three σ uncertainty of the thrust is [Formula: see text]N for the measurement of the cold gas thruster. The scheme provides a thrust measurement with higher precision and stability.

With the development of electric space propulsion and all-electric propulsion technologies, the application range of the Hall effect thruster (HET) has gradually expanded. As an important part of the HET, the magnetic field plays a decisive role in its performance. In the development of versatile HETs, it is necessary to comprehensively and thoroughly understand the effects of the magnetic field on the HET discharge characteristics. In this paper, a HEP-100X thruster with multiple degrees of freedom in terms of magnetic field control is used to study the effects of the peak magnetic field position on the thruster discharge characteristics. The results indicate that the peak magnetic field position can effectively control the main ionization zone position and affect the ionization rate. The thruster has the best comprehensive discharge performance when the peak magnetic field position is located near the channel exit. Further analysis reveals that the performance improvement is mainly due to the reduced ion loss on the wall surface and plume divergence half-angle, and the increased current utilization efficiency and voltage utilization efficiency. The HEP-100X shows the above trends under various flow conditions, and the anode efficiency is the highest when the anode flow is 50 sccm. In this condition, the propellant is sufficiently ionized and the ion loss on the wall surface is small. This research provides the necessary support for a comprehensive understanding of the role and significance of the magnetic field in the thruster discharge process, and has important significance for the design optimization of multifunctional Hall thrusters and subsequent research.

Hall thrusters must be frequently ignited and extinguished during operation in orbit. The thruster is typically extinguished by terminating the anode voltage. However, the equilibrium state of the plasma in the discharge channel is lost when the external electric field disappears. This consequently changes the state of the plasma, causing rotating spokes to appear. However, spoke rotation ceases after nine rotations. Therefore, in this study, a high-speed camera was used to study the instantaneous spoke rotations of a Hall thruster during the extinguishing process. Additionally, the characteristics of the azimuthal rotating spoke during this process were studied. It was found that, because the anode voltage does not instantaneously decrease to 0 V during the extinguishing process, the spoke mode changes from multi-mode to single-mode. Furthermore, as the voltage dropped from 250 to 0 V, a single-mode spoke appeared, and the spoke speed linearly decreased.

The use of krypton in the field of electric propulsion has become a key research topic owing to its high specific impulse and high reserves. However, because krypton has features such as a small ionization cross section and high ionization energy, its ionization performance is relatively low, thereby increasing the actual specific impulse loss of the krypton Hall thruster in comparison with its theoretical value. Therefore, to use of krypton as the propellant of the Hall thruster instead of xenon, it is necessary to study the optimization of its ionization process. In this study, a gas distributor with a rotating propellant supply mode is designed, considering factors such as the velocity and density of the velocity of neutral atoms, which affects the ionization process. The distribution of neutral atom parameters in the discharge channel is changed by the rotation; and its influences on the propellant ionization and other performance parameters of the Hall thruster are experimentally analyzed with respect to the magneto-ampere, volt-ampere, and flow rate-ampere characteristics. The results demonstrate that the rotating propellant supply reduces the axial velocity of neutral atoms, increases the density and circumferential motion distance, and thus improves the ionization efficiency of the krypton Hall thruster. Furthermore, the performance parameters, such as thrust and efficiency, are also improved, and the plume divergence angle is reduced. When the discharge voltage is 450 V and the anode flow rate is 60 sccm, the rotating propellant supply can increase the anode efficiency of the axial propellant supply mode from 46.2% to 53.2%. However, the plume divergence half-angle reduces from 39.2° to 35.5°. In addition, an increase in the anode flow rate and discharge voltage continuously increases the performance promotion in the rotating propellant supply mode.

In this work, a krypton Hall thruster is used to study the influence of low-frequency oscillation on the focusing characteristics of the plasma beam. The experiment results show that the plume dive...

A magnetically shielded Hall thruster (MSHT) has a significantly longer service life than a conventional unshielded Hall thruster (USHT) as it shifts the magnetic field of maximum strength from the channel interior to the exterior. In this study, it was experimentally determined that the influence of the radial position of an externally mounted hollow cathode on the performance of an MSHT is quite different from that of a USHT. The measured plasma parameters demonstrate that in addition to the coupling voltage loss and plume divergence loss, the electron cross-field transport loss (not considered previously and introduced by the outward shifting of the magnetic field) is also important to explaining the performance variation in the MSHT. This study refines the coupling theory between the cathode and Hall thruster and provides a valuable reference for determining the radial position of an externally mounted hollow cathode in an MSHT.

Breaking through the corona discharge current limit and improving the ionization and acceleration process are beneficial to improve the performance of the electroaerodynamic thruster. In this paper, a dual-frequency source of DC and NSP (nanosecond pulse) are applied to generate ionic wind. Electrical, optical and thrust characteristics are compared for the electroaerodynamic thruster with and without the NSPD (nanosecond pulse discharge). The experimental results indicate that the thrust characteristics are enhanced under the effect of dual-frequency sources. Moreover, the inception DC voltage to generate ionic wind is much lower.

In this experimental study, the ceramics of a cylindrical Hall thruster with a magnetically insulated anode structure at the bottom of a discharge channel was found to be eroded. The potential, distribution of the ion number density, ion velocity in the channel, and the power density into the bottom of the channel were analyzed through a particle-in-cell numerical simulation. The results of this study indicate that the electrons move along the magnetic line to the bottom of the channel where the negative charges accumulated form a negative potential. Under a potential action, some low-energy ions in the channel move toward the bottom of the channel in an accelerating manner, causing an erosion of the ceramic material; the deposition power density reaches the peak value at the bottom center and gradually decreases in a radial direction, which is consistent with the actual erosion occurring at the bottom of the channel.

HET72-VC is a kW-class Hall effect thruster with a variable channel characterized by high thrust and power densities. In this work, an experimental study of the effect of magnetic field configuration on the discharge characteristics of HET72-VC is carried out. By separately adjusting the current through the front and rear coils to change the magnetic field configuration inside the channel, a change in the plume is observed and the discharge performance parameters are measured. Experimental results show that the effects of reducing the front coil current and increasing the rear coil current on the thruster discharge are consistent. The plume gradually changes from a hollow cone with a clear boundary into a solid cone, the thrust increases by about 3%, and the anode efficiency increases by about 2.5%. Theoretical analysis shows that the degree of inclination of the magnetic lines of force plays an important role on the electron conduction and ion acceleration. When the angle between the magnetic lines of force and the channel centerline becomes larger, the discharge performance improves. This study helps in providing a deeper understanding of the working characteristics of this type of thruster, and can provide important guidelines for its structure design and optimization.

A high speed charged coupled device (CCD) camera was used to examine the plume features over time when the cathode was located inside and outside the magnetic separatrix. Due to the different positions of the cathode, there are obvious differences in the electron impact excitation process, the characteristics of the plasma bridge, and the transition process from the end of ignition to the steady-state discharge process. The main reason for these differences may be due to the different conduction paths followed by emitted electrons into the acceleration channel. The CCD images method can be used as a technique to characterize the ignition process of Hall thruster.

It is commonly accepted that high neutral density or low bulk axial velocity will efficiently enhance ionization. At present, all the operation of neutral gas flow inside the Hall thruster is an attempt to reduce axial velocity of neutral gas and extend residence time. Based on the idea, we proposed the azimuthal diversion rail (ADR) Hall thruster for the first time in preliminary work, and provided a kind of brand new method to reduce axial velocity of neutral gas. Compared to other modes, such kind of mode features simple structure, light weight and significant effect, in which axial movement is transformed to circumferential movement through elastic collision, thus the residence time and neutral density in the channel can be increased, ionization degree and discharge performance are improved accordingly. However, we found in the ADR research process made at later stage, the location of ADR in the discharge channel exerts significant impact on discharge. Therefore, this paper studies the effect of the ADR location on the discharge performance of Hall thrusters. The location of the ADR can affect the distribution of the propellant density in the channel of the Hall thruster, thereby affecting the propellant utilization and performance. The thrust, specific impulse, efficiency and propellant utilization of the ADR are measured in three different locations in the channel, respectively. The propellant density in the ionization zone is higher when the ADR is flush with the anode top surface. Furthermore, the propellant utilization can be increased by 12% and 9% compared with that at the bottom and the middle of the anode, respectively, resulting in the thrust being increased by up to 3.2 mN (10%) and 2 mN (8.5%) and the anode efficiency being increased by up to 9% and 6%. The location of the ADR has a significant effect on the performance of the thruster. The sensible placement of the rail can effectively increase the propellant density in the ionization zone to improve the performance. The results of the study can be used to guide the design of Hall thrusters with ADR.

A particle-in-cell Monte Carlo collision model of a discharge chamber is established to investigate the start-up process of a miniature ion thruster. We present the discharge characteristics at different stages (the initial stage, development stage, and stable stage) according to the trend of the discharge current with time. The discharge current is the sum of the sidewall current and the backplate current. During the start-up process, the sidewall current lags behind the backplate current. The variation and distribution characteristics of the discharge current over time are determined by the electron density distribution and electric potential distribution.

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.

To improve the performance of thrusters by using two permanent ring-shaped magnets to push a magnetic field downward, we propose an annular–cylindrical combined-channel Hall thruster and numerically study its performance. The results indicate that, compared with simple annular channels, the annular–cylindrical combined channel can effectively increase the neutral gas density contained within it and increase the degree of ionization, efficiency, thrust, and specific impulse. Moreover, the sputtering zone of discharge channel is in front of the permanent magnets, i.e., wall erosion occurs upon ion bombardment during discharge. However, ions cannot bombard the permanent magnetic rings, thus guaranteeing a constant magnetic field and long discharge lifetime.

The characteristics of ionic wind under the magnetic field are studied by using a needle-to-mesh electrode. With the increasing of magnetic field intensity, the amplitude of Trichel pulse decreases and the pulse frequency increases significantly; the ionic wind speed clouds in the yOz plane shift from concentric circle to eccentric ellipse, and the ionic wind profiles along y-axis gradually transfer from a symmetrical distribution to a biased state; the maximum wind speed value and the corresponding electrical-to-kinetic energy conversion efficiency are also increased. These results illustrate that the magnetic field could adjust the ionic wind.

The reliability of cathode is critical to electric propulsion systems. Although researchers have carried out many life tests on hollow cathode, the discharge current is almost steady when the cathode is independently tested for life. Actually, when it is coupled with the thruster, the discharge current is with large amplitude low-frequency oscillation. Therefore, we suggest a new external circuit for a cathode-independent life test, which could simulate the characteristics of discharge current oscillation when the cathode is coupled with Hall thruster. We carried out 160 h of life test using the normal external circuit and the new external circuit, and the variation characteristics of the cathode orifice area are also studied during the life test. The results show that under the normal external circuit, the growth rate of the cathode orifice area initially increases and then decreases gradually with the increase of the time of life test, whilst the cathode orifice area in the new external circuit linearly increases. The new external circuit can provide a new method to simulate the discharge current oscillation when the cathode is coupled with Hall thruster during the independent life test of the cathode.

A 200-W Hall thruster was designed using permanent magnets placing the axial maximum magnetic field outside of the channel, and the anode/gas distributor as an integrated U-shaped structure. A split structure is adopted for the discharge channel to conveniently change the wall material. With the initial conditions that the anode mass flow is maintained at 0.8 mg/s, 1.0 mg/s and 1.2 mg/s over a voltage range of 150–400 V (at 50 V intervals), the discharge properties were determined for the two thruster models with the channel walls composed of graphite and boron nitride (BN). The results demonstrate that under identical operating parameters, the properties of the thruster with the graphite channel walls are similar to the properties of the thruster with the BN channel walls. The maximum difference of the discharge current between the two wall materials is 6.2%; the maximum difference of the thrust and the specific impulse is 3.3%, and that of the anode efficiency is 1.7% (absolute value). These differences are smaller than the corresponding parameter differences observed from changing wall materials in other common Hall thrusters.

The ignition methods used by micro-radio frequency (RF) ion thrusters have a disadvantage, that is, the starting voltage and flow rate are obviously higher than the rated value, which will easily damage the grid after long-term use. To decrease the starting voltage and flow and reduce the damage to the grid, a new ignition system is proposed in this paper. This system uses an intake pipe as the ground electrode, has an inductance coil and a pre-ionization chamber, and enables the miniature RF ion thruster (Harbin Institute of Technology’s RF Ion Thruster 4, HRIT-4) to ignite at the rated voltage and flow by means of strong electric field breakdown and electromagnetic coupling. The experimental results show that when the flow rate is 1.0 SCCM, the ignition voltage is lower than 1900 V, and when the flow rate is 1.5 SCCM, the ignition voltage is lower than 1400 V.

The objective of this study is to investigate the effect of pulse frequency on the discharge characteristics of a micro-cathode arc thruster. We used an intensified charge-coupled device (ICCD) and high-resolution spectrometer to capture the plasma emission process of a micro-cathode arc thruster. The change in the valence ion ratio under different discharge frequencies of the thruster is studied with respect to the change in light intensity. The relationship between the pulse frequency and Ti + ion ratio, cathode emission plasma bunch velocity, and normalized thrust are studied. The spectral and electrical test results demonstrate that the proportion of high-energy ions emitted from the cathode increases with the increase in interpole discharge frequency, and the ion bunch velocity and normalized thrust of the thruster are both improved.