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In this paper, a new “convex” external magnetic pole structure is proposed. With this structure, two different configurations of the cathode inside and outside the magnetic separatrix can be realized by changing the position of the magnetic separatrix instead of changing the position of the cathode in the radial direction. Furthermore, the discharge plume, coupling voltage, and performance of the thruster under different configuration conditions are studied experimentally. The experimental results indicate that, when the cathode is located inside the magnetic separatrix, the effective acceleration voltage is higher, the coupling voltage between the cathode and the thruster is lower, and the thruster performance (including thrust, specific impulse, and efficiency) is higher. When the cathode is located outside the magnetic separatrix, the effective acceleration voltage is lower, the coupling voltage between the cathode and the thruster is higher, and the thruster performance is degraded. When the cathode is located inside the magnetic separatrix, the thrust and specific impulse can be increased up to 2.3%, and the efficiency—up to 4.6%. This study provides a new method for the design of the magnetic separatrix and is of great importance for the coupling-matching design of the cathode and thruster. [ABSTRACT FROM AUTHOR]

A low-power Hall-effect thruster was designed with two permanent magnet rings. This Hall-effect thruster contains a symmetrical double-peak magnetic field with a gradient larger than that of conventional Hall-effect thrusters. The matching of the anode position with the magnetic field determines the performance of the thruster to a very large extent. This study investigates the laws and mechanisms that govern the front end of a U-shaped hollow anode at the inner magnetic separatrix, the outer magnetic separatrix, and the area between them and influence the discharge characteristics of the thruster. The study shows that with the increase of anode length, the ionization and acceleration zones are pushed down toward the channel outlet and even into the plume region. At the same operating point, both the thrust and the efficiency are the largest when the anode is placed between the inner and outer magnetic separatrices. When the anode is placed at the inner magnetic separatrix, both the thrust and the efficiency are small because of the heavy energy loss on the walls, despite the high degree of ionization. Finally, when the anode is at the outer magnetic separatrix, the performance of the Hall-effect thruster is the poorest because of the lower degree of ionization and larger divergence angle of the plume upon the shift of the ionization zone toward the plume region. [ABSTRACT FROM AUTHOR]

The magnetic field distribution of Hall thrusters has a crucial impact on its performance. Studies have mostly focused on the magnetic field distribution within the channel and near the channel exit, but less attention has been paid to the magnetic field distribution in the near-field plume region. Two different magnetic field distributions were designed. The influence of the magnetic inclination in the plume region on the performance of a low-power Hall thruster was investigated using a particle-in-cell (PIC) numerical simulation and experimental study. The results indicate that the magnetic field with inclined inward can effectively improve the performance of Hall thrusters, relatively increasing the thrust by 3.6%–9.6%, anode specific impulse by 3.8%–9.8%, and anode efficiency by 2.5%–5.5% at a fixed flow rate. It can also reduce the plume divergence angle, and the maximum decrease in the plume divergence half-angle is approximately 7°. The main reason is that the radial electric field in the plume region under an inward-inclined magnetic field is lower than that with an outward-inclined magnetic field, thus making the radial velocity of ions in the former magnetic field lower than that in the latter magnetic field, ultimately driving more ions to the thruster center. • The inclination of magnetic field lines in the plume region can affect performance of Hall thrusters. • The magnetic field with inclined inward in the plume region can enhance performance and reduce plume divergence angle of Hall thrusters. • When designing Hall thrusters, the magnetic field lines in the plume region should be kept inclined towards the center of thruster. [ABSTRACT FROM AUTHOR]

Traditional Hall thrusters can ionize gas inside the channel and accelerate ions outside it by moving the peak magnetic field out of the channel, which improves the thruster performance. In this study, the effects of the peak magnetic field location on the discharge characteristics of a 100-W Hall thruster with large-gradient magnetic field were investigated by changing the ratio of the magnetic field intensity at the channel exit to the peak magnetic field intensity (Br exit /Br max). The experimental results show that the discharge performance decreases significantly when Br exit /Br max < 1. Moreover, the PIC numerical simulation and neutral gas simulation results demonstrate that the ionization rate inside the channel reduces and the ionization proportion outside the channel increases when Br exit /Br max decreases, thereby reducing the performance. When Br exit /Br max = 1, under the anode flow of 5.5 sccm and discharge voltage of 250 V, the thrust, anode specific impulse, propellant utilization efficiency, and anode efficiency of the 100-W thruster were 6.4 mN, 1210 s, 68.9%, and 38.5%, respectively, which represent respective improvements of 16.2%, 16.4%, 13.0%, and 30.0% (relative value) compared with the condition when Br exit /Br max = 0.9. These results provide a reference for the performance optimization of 100-W Hall thrusters with a large-gradient magnetic field. • The Effects of peak magnetic field location on performance of a 100W large gradient magnetic field Hall thruster is studied. • The ionization and discharge performance parameters of thruster under different Br exit /Br max conditions are given. • When the value of Br exit /Br max decreases from 1, the overall performance of the thruster decreases significantly. • The decrease of Br exit /Br max worsens the ionization process and reduces the overall performance of the thruster. [ABSTRACT FROM AUTHOR]

Electric propulsion systems with high-specific impulses have replaced chemical propulsion systems in many space missions. The aft-loaded magnetic field technology of Hall thrusters moves the ionization and acceleration processes downstream of the channel by varying the magnetic field distribution. Consequently, ion bombardment of the channel walls is inhibited, and the service life of the Hall thrusters is substantially increased. However, neutral gas leaks because of the rapid diffusion near the channel outlet, where strong ionization occurs. Thus, the propellant atoms are ionized insufficiently, resulting in a decline in the performance. Therefore, an aft-loading design for the neutral gas flow field was developed to optimization distribution of the neutral gas in this study. A 1.5 kW Hall thruster was verified experimentally. The experimental results show that the aft-loaded neutral gas flow field significantly improved the ionization and acceleration processes. The propellant utilization efficiency increased by 4–8% within the discharge voltage range of 300–900 V. The ion energy distribution moved toward the high-energy direction significantly, promoting an overall improvement in the performance, with a thrust increase of 7.3–11.5 %. The anode efficiency increased from 49–57 % to 58–61 %. The results of this study are significant for the design of high-performance, long-life Hall thrusters. • The aft-loading design of gas flow is realized using the special topology of the hybrid-wall Hall thruster. • The ionization distribution of aft-loaded neutral gas flow field is concentrated in higher potential region. • The aft-loaded neutral gas flow moves the ionization region downstream of the channel. [ABSTRACT FROM AUTHOR]

Poor performance limits the wider application of 100-W-power class Hall thrusters. The effects of position matching between the anode and the zero-magnetic-field region (ZMFR) on the discharge process and performance improvement of 100-W Hall thrusters were investigated. The experimental results demonstrate that appropriately widening the ZMFR downstream of the anode improves the ion current and thrust, promotes plume focusing, and optimizes thruster performance. The thrust and anode efficiency is enlarged by 7.6 % and 20 % (relative value), respectively, when the ZMFR downstream of the anode is expanded by 0.2 L (L is the channel length). The simulation results indicated that widening the ZMFR promoted the expansion of the high-ionization zone to the bottom of the channel, and increased the overall ionization rate. Moreover, as the ZMFR increases, the effective ion acceleration voltage increases. However, widening the ZMFR also aggravated the ion-wall interaction and reduced the propellant utilization rate. Therefore, the performance of the thrusters exhibited an optimal range as the length of the ZMFR increased. In addition, increasing the ZMFR did not affect the life of the thrusters. • The effects of position matching between the anode and zero magnetic field region on discharge characteristics are studied. • The discharge characteristic parameters of thruster with different lengths of ZMFR downstream of the anode are given. • Appropriately increasing the ZMFR can improve the ion current and thrust, thereby improving the anode efficiency. • The position matching between the anode and ZMFR affects the ionization process and propellant utilization ratio. [ABSTRACT FROM AUTHOR]

The inward deflection of the excitation magnetic field was found in a Hall thruster voltage-varying experiment. The influence of Hall current magnitude and radial distribution on the total magnetic field was analyzed through magnetic field simulations. The probable reason why the excitation magnetic field deflected inward evidently at high discharge voltages (＞600 V) was obtained by combining the simulation results and theoretical analysis. This study provides qualitative guidance on the design of the excitation magnetic field in high-specific-impulse Hall thrusters. • Hall current induces an outward deflected magnetic field. • Magnitude and asymmetry of Hall current have an equivalent effect on magnetic field deflection. • An inward deflected excitation magnetic field is necessary to obtain a symmetrical total field. [ABSTRACT FROM AUTHOR]

The channel wall shape of a magnetically shielded Hall thruster is typically designed to be tangential to the near-wall magnetic field line, which significantly constrains wall design freedom. In this study, the wall chamfer was expanded based upon tangent matching, and the effectiveness of magnetic shielding was determined based on the wall color after the experiments. The experiments indicated that the thruster would maintain the same high performance and no visible erosion at constant power levels and constant anode mass flow rate levels in the expanded chamfer wall, even if the wall was not perfectly tangent to the grazing line. The results provide new insights into the design of the topology of magnetically shielded Hall thrusters. • Good magnetically shielded effect remains when both endpoints of chamfered wall is over-tangent to magnetic field line. • Over tangent of wall downstream endpoint affects the discharge little and so a high level of thruster performance remains. • Over-tangent wall shape is much easier to achieve than the perfect tangent one, thereby expanding wall design freedom. [ABSTRACT FROM AUTHOR]

In order to develop multi-mode thrusters for all-electric propulsion spacecraft, a double-stage Hall thruster is designed and investigated experimentally. By applying two independent non-emissive electrodes and a double-peaked magnetic field in the double-stage Hall thruster, the propellant can be ionized in the first stage and then accelerated in the second stage. Experiment results revealed that double-stage discharge effectively improves thruster performance in high specific impulse working mode by reducing the electron current. A one-dimensional model is used to discuss the effects of discharge parameters on ionization distribution theoretically. As a conclusion, ionization distribution (in terms of position and length) in high specific impulse mode (mode I) is significantly different compared to high-thrust working mode (mode F). This double-stage Hall thruster provides a double-stage discharge in mode I to enhance the ionization in the channel and a single-stage discharge in mode F to reduce the ion wall-loss, achieving high efficiency in both working modes. [ABSTRACT FROM AUTHOR]

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. • Hall thruster can operate in a wide power range under unsymmetrical magnetic fields. • Inward-inclined magnetic field can improve thruster discharge performance. • Outward-inclined magnetic field is conducive to prolong thruster service life. [ABSTRACT FROM AUTHOR]

In recent years, high-voltage and high-specific-impulse Hall thrusters are being developed. However, the efficiency of the Hall thruster does not increase monotonically with the discharge voltage, but reaches peak at an intermediate voltage, which limits the ability of high-voltage Hall thruster. Previous studies indicate that the sharp increase of the wall energy loss at high voltages dominates the occurrence of the efficiency peak. Therefore, a peak-pushed-outside (PPO) magnetic field is designed in this study, which is expected to diminish the wall energy loss. Experimental results show that the PPO magnetic field can push the propellant ionization and acceleration process downstream, reduce the wall energy deposition at high voltages effectively, and therefore improve the efficiency peak value and increase the voltage corresponding to the efficiency peak. This is helpful to enlarge the high-voltage operation range of Hall thrusters. However, the discharge oscillation rises up significantly at high voltages, and the thruster performance degrades at low voltages, which requires further investigation. • Peak-pushed-outside magnetic field reduces wall energy deposition in Hall thrusters greatly. • Peak-pushed-outside magnetic field promotes the efficiency peak and the corresponding discharge voltage in Hall thrusters. • Peak-pushed-outside magnetic field is suitable for high-voltage Hall thrusters. [ABSTRACT FROM AUTHOR]