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

In steady-state operation of Hall thrusters excited by permanent magnets, the existence of temperature difference between the inner and outer permanent magnets will cause the deviation of the magnetic field configuration from the design value, thus affecting the discharge process. The simulation results show that the ion power loss on the inner wall increases by over 7.5% when the temperature difference between the inner and outer permanent magnets reaches to 140 ℃. The main reason is that the coercivity of the inner permanent magnet decreases more at higher temperature, and the magnetic field lines will incline toward the inner wall, resulting in the increment of the radial component of the electric field pointing to the inner wall. An optimized magnetic field, obtained by moving the inner permanent magnet outward in an appropriate manner, is proposed to alleviate the inner wall erosion. The optimized magnetic field has a near-symmetrical configuration, especially the nearly equal length of intersection lines of the magnetic field lines with the inner and outer walls, which is contributed to reduce the radial component of the electric field and preventing the inclination of the main ionization zone toward the inner wall, so that the peak value of ion power deposition on inner wall can be reduced by more than 50%. Based on the illustrated features and mechanism of wall erosion, an effective and easy-to-implement optimization scheme was proposed in this work to provide a useful reference for the design of long-life Hall thrusters with large height-radius ratio. [ABSTRACT FROM AUTHOR]

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. [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 strength and shape of the magnetic field are the core factors in the design of the Hall thruster. However, Hall current can affect the distribution of static magnetic field. In this paper, the Particle-In-Cell (PIC) method is used to obtain the distribution of Hall current in the discharge channel. The Hall current is separated into a direct and an alternating part to calculate the induced magnetic field using Finite Element Method Magnetics (FEMM). The results show that the direct Hall current decreases the magnetic field strength in the acceleration region and also changes the shape of the magnetic field. The maximum reduction in radial magnetic field strength in the exit plane is 10.8 G for an anode flow rate of 15 mg/s and the maximum angle change of the magnetic field line is close to 3° in the acceleration region. The alternating Hall current induces an oscillating magnetic field in the whole discharge channel. The actual magnetic deformation is shown to contain these two parts. [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]

The theoretical specific impulse of Hall thrusters using a krypton propellant is much higher than that of those using xenon. However, the actual benefits of this improvement are limited by the difficulty in achieving krypton atom ionization, and its efficiency is much lower than that of xenon. In this study, the anode specific impulse and anode efficiency of Hall thrusters using krypton propellant were improved by adding a small quantity of xenon. A dual-channel supply of xenon and krypton was achieved by optimizing the discharge channel structure based on the design of the aft-loaded magnetic field. The effects of the xenon and krypton supply method and xenon fraction on the discharge characteristics of the Hall thruster were investigated by conducting discharge experiments using the mixed propellant. The results indicated that injecting a small quantity of xenon significantly improved the ionization of krypton, improved the ionization and acceleration efficiency of the thruster, and fully utilized the high specific impulse characteristics of krypton. Furthermore, the addition of a small quantity of xenon also significantly increased the upper limit of the discharge voltage for stable operation using krypton from 500 V. At the maximum tested xenon fraction, the maximum discharge voltage was loaded to 900 V. At a discharge voltage of 800 V, the optimal anode efficiency and anode specific impulse increased by 4.5 % and 534 s, respectively, compared with those for pure xenon propellant (with an anode efficiency of 54 % and anode specific impulse of 3034 s). The results of this study are of great significance for the design of high-efficiency, high-specific-impulse, and low-cost Hall thrusters. • A dual-channel gas supply structure is proposed, which can supply two kinds of gases into the discharge channel individually. • Thruster performance is optimal when krypton is supplied downstream and auxiliary xenon is supplied upstream. • High-voltage operating ability under krypton is greatly improved with the assistance of a small quantity of xenon. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hall thrusters generally use a U-shaped insulated wall to form an annular discharge channel. As high-power and high-specific-impulse Hall thrusters develop, the disadvantages of this conventional topology—in terms of material and mechanical strength, processing, and manufacturing—are gradually being exposed. Therefore, in this study, a new wall material was employed, and its effects were investigated numerically and experimentally. A boron nitride ceramic wall was retained in the strong discharge area owing to its excellent secondary electron emission characteristics; while a metallic wall was applied upstream of the channel, forming a segmented hybrid wall. A Hall thruster with an aft-loaded magnetic field, which offers a long lifetime, was adopted for this study. The particle-in-cell simulation shows that the length of the metallic wall has a significant impact on thruster performance. The same trend was observed in the experiments. Under the optimal metallic wall length, the anode efficiency is improved by approximately 4% compared to that of the ceramic-wall-only case. The physics involved is analyzed and qualified by comparing the simulated and measured results. The findings of this study provide valuable guidance for the optimal design of high-power, high-specific-impulse Hall thrusters. • Metal-ceramic hybrid channel wall improves high-voltage performance of Hall thrusters. • Optimal length of metallic segment exists and is strongly related to magnetic field. • Too long metallic segment augments electron wall loss and then ionization loss. [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]

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]