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Abstract 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. Highlights • Effects of the azimuthal diversion rail location on performance of Hall thrusters is studied. • It is proved the rail placement can increase the propellant density in the ionization zone. • Azimuthal diversion rail location can be used to improve the hall thruster performance. [ABSTRACT FROM AUTHOR]

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 high amplitude pulse current during Hall thruster start-up is an important source of electromagnetic interference, which impacts the safety and reliability of the propulsion system. The characteristics of the pulse current, including the pulse current's integrated area, peak value, and transient time, are studied experimentally and theoretically under different Hall thruster discharge parameters. Results show that the pulse current's integrated area is determined by the atom density in the channel before Hall thruster start-up; the effects of coil current on the peak value and transient time of the pulse current are negligible. As the discharge voltage and mass flow rate increase, the pulse current peak value increases, the pulse current duration is inversely proportional to the discharge voltage and directly proportional to the mass flow rate. [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]

Micro-nano satellites show considerable potential in the application of low-orbit satellite networks, and low-power Hall effect thrusters (HETs) that provide the impetus for them have also attracted considerable attention worldwide. However, the relatively large surface-to-volume ratio of low-power HETs leads to significant loss of ions on the wall surface. After the channel width is increased or the ionization area is moved outward, ensuring sufficient ionization of the propellant is very difficult, and thus its integrated performance is not high. Thus, in this study, a 100-W permanent magnet HET with an aft-magnetic field is considered as the carrier to investigate the effect of gas supply direction on the thruster discharge characteristics through a simulation and experiments. Results indicate that under the same working conditions, adopting the circumferential direction gas supply mode effectively increases the density of the propellant in the ionization zone (up to 7%), improves the propellant ionization rate (up to 12.7%), and improves integrated discharge performance (the anode efficiency can be increased by up to 5.3%). In addition, the performance optimization effect of this mode is more evident under the working condition of low flow. When combined with an aft-magnetic field, this method is an effective means to ensure high-efficiency discharge of a low-power HET, which can be used as a reference for the miniaturization development of HETs. • The circumferential direction gas supply mode increases the density and ionization rate of propellant. • The performance optimization effect is more evident under the working condition of low flow. • The circumferential direction gas supply mode is an effective means to ensure high-efficiency discharge of low-power HET. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Electrons move to the bottom of the channel and form a negative potential. • Low-energy ions cause the erosion of bottom of the channel. • The deposition power density reaches a peak value in the center of the bottom channel and gradually decreases with the radial coordinate. [ABSTRACT FROM AUTHOR]

In this study, the effect of pulse frequency on the discharge and plume characteristics of Hall thrusters under pulsating operation is investigated. The experimental results show that the discharge current and thrust decrease as the frequency increases to the range of 30–90 kHz. The efficiency of the thruster is negatively correlated with the pulse frequency, and the pulse frequency minimally affects the plume divergence angle and ion current. It is found that an increase in the pulse frequency decreases the secondary electron emission flux on the wall and the near-wall conduction rate of electrons in the channel, thus consequently decreasing the electron current. An increase in the electron current share improves the current-utilization efficiency. In addition, as the frequency increases, the ion power loss on wall increases and the ion acceleration becomes less effective, thus resulting in a decrease in thrust. The combined effect of these two factors results in an increase in the anode efficiency as the frequency increases. • The effect of pulse frequency on the discharge and plume characteristics of Hall thrusters under pulsating operation were investigated. • Increasing the pulse frequency decreases the secondary electron emission flux, which reduces the rate of electron-in-wall conduction in the channel, thus resulting in a lower electron current. • As the pulse frequency increases, the ions power loss on wall increases leading to poorer ion acceleration and a reduction in thrust. [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]

In this study, the material loss relationship between the electrodes of a micro-cathodic arc thruster was investigated by adjusting the input voltage. The crater morphology of the micro-cathodic arc thruster was observed with a scanning electron microscope. The internal crater material was analyzed with an energy spectrum analyzer. On this basis, the arc path is obtained and the material loss of the structure between the electrodes of the micro-cathodic arc thruster was studied through further numerical simulation. The experimental and simulation results show that with a change in the Power processing unit (PPU) input voltage of the micro-cathodic arc thruster, the material distribution in the cathode crater and the discharge channel between the electrodes changed, affecting the bombardment of ions between the electrodes of the thruster on the insulating structure and conductive coating. In engineering applications, regulation of the arc breakdown path can effectively reduce the total energy of ion bombardment on the wall. • Study on micro-morphology and composition distribution characteristics of arc crater of micro-cathode arc thruster. • Study on the distribution characteristics of PPU input voltage and discharge channel between thrusters. • The ion bombardment on the wall under different discharge channels is simulated. • With the increase of PPU input voltage, the dominant factor of inter-electrode structure loss changes. [ABSTRACT FROM AUTHOR]

An analysis of the discharge behavior of a symmetrically designed Hall-effect thruster (HET) under an asymmetrical condition will aid the understanding of the working characteristics of HETs from different perspectives. Therefore, in this paper, with experimental methods, the asymmetrical gas distribution inside the channel of a HET was realized by supplying the gas asymmetrically, and changes in both the performance and plume parameters with the degree of asymmetry were measured. Both the discharge current and thrust were found to vary nonlinearly with the degree of asymmetry; moreover, the discharge mode also shifted, as observed from the variations in the discharge current and oscillation. Furthermore, the relationships between the plume ion current and energy distributions and the degree of asymmetry were determined and further used to explain the nonlinear change in the thrust. Overall, the findings of this study strengthen the understanding of the physics of HET discharge. • Variations of performance and plume parameters show consistency as the degree of asymmetrical neutral distribution changes. • Discharge of high-density region under an asymmetrical neutral distribution dominates the overall thruster operation status. • Deflection of plume are the decisive factors for the reduced thrust under an asymmetrical neutral distribution. [ABSTRACT FROM AUTHOR]

In this study, the evolution of the plasma parameters of a Hall thruster under the pulsating operation was investigated using the particle-in-cell (PIC) model. The results show that the current waveform of the simulation results was almost the same as that of the experimental results under the same pulse parameters and working conditions. The average thrust of the simulation results was close to the experimentally measured thrust, so the accuracy of the simulation model was confirmed. The peak thrust of the Hall thruster under pulsating operation was approximately three times that under direct current (DC) operation. The simulation results show that the ionization rate increases rapidly under pulsating operation and is several times higher than that under DC operation. An increase in the number of ions led to an increase in the discharge current. Meanwhile, owing to the increase in the potential drop in the acceleration zone of the Hall thruster under pulsating operation, the ion acceleration effect was improved. These are the main reasons for the rapid increase in the instantaneous thrust during the pulsating operation. • A PIC model for Hall thruster under pulsating operation was proposed. • Comparison of simulation and experimental results of discharge characteristics and thrust verified the accuracy of the model. • The evolution of the plasma parameters of a Hall thruster under the pulsating operation was investigated. • The increase in the potential drop and ionization rate are the main reasons for the rapid increase in the instantaneous thrust. [ABSTRACT FROM AUTHOR]

The dielectric properties of a dielectric material significantly affect the gas-solid interface discharge characteristics of the surface dielectric barrier discharge (SDBD) and surface space charge accumulation. In this study, new high dielectric composite dielectrics were prepared from barium calcium zirconate titanate nanoceramic particles (BZCT-NPs) using olyvinylidene luoride (PVDF) as a matrix. The impact of the amount of BZCT-NPs incorporated in the dielectric was investigated, and the influence mechanism of the new dielectric on the performance of SDBD ion wind thrusts was studied. Dielectrics with 3% (v/v) and 5% (v/v) BZCT-NPs/PVDF had significantly higher dielectric constants, 111% ± 2% and 135% ± 5%, respectively, compared to dielectrics made only of PVDF. The loss angle tangent values increased by 673% ± 33% and 707% ± 33%, respectively. The discharge charge increased by 54% ± 4% and 108% ± 13%, and the discharge time in one cycle increased by 23% ± 6% and 13% ± 4%, respectively. The single-point maximum wind speeds increased by 23.2% and 8.7%, respectively. The maximum thrust-to-power ratio of the 0% (v/v), 3% (v/v), and 5% (v/v) BZCT-NP dielectrics were 1060 μN/kW, 3120 μN/kW, and 2436 μN/kW, respectively. Interestingly, the minimum operating voltage of the thrusters decreased with increasing volume fraction of BZCT-NP, while the thrust-to-power ratio of the thruster increased significantly with higher levels of nanoceramic particles. The starting operating voltage of the 3% (v/v) BZCT-NPs/PVDF dielectric decreased by approximately 35% and 50% compared to the 5% (v/v) BZCT-NPs/PVDF and PVDF dielectrics, respectively, while the maximum thrust-to-power ratio increased by 194.3% and 129.8%, respectively. • Compared with PVDF, the discharge charge of 3 vol% BCZT-NPs/PVDF and 5 vol% BCZT-NPs/PVDF increased by 54% ± 4% and 108% ± 13%, respectively, and the discharge time increased by 23% ± 6% and 13% ± 4%, respectively. The addition of nano-ceramics can effectively regulate the space charge accumulation on the dielectric surface. • The maximum wind speed of the three thrusters is 1.12 m/s, 1.38 m/s and 1.27 m/s, respectively. When 3 vol% BCZT-NPs/PVDF acts as dielectric barrier, the wind speed generated by the thruster is the maximum. • The maximum thrust density is about 1080 μN/m, 860 μN/m and 710 μN/m, respectively. The maximum thrust-power ratios were 1060 μN/kW, 3120 μN/kW and 2436 μN/kW, respectively. and the maximum thrust to power ratio is increased by 194.3% and 28.1%, respectively. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Plume shape is strongly modulated by magnetic field configuration. • Plume shape of a solid cone rather than a hollow cone represents good performance. • Magnetic field configuration impeding electrons strongly yields good performance. [ABSTRACT FROM AUTHOR]

To explore the effect of energy input on the discharge characteristics of a micro cathode arc thruster, the relationships between the different input PPU voltages of the micro cathode arc thruster and the plume shape, arc characteristics, thruster propulsion performance, and working fluid ionization are characterized in this research. The results obtained using a high-speed camera indicate that the change in the thruster's energy input affects the plume contraction. Further, the results of spectroscopy and electrical testing analyses show that an increase in the thruster input voltage prolongates the arc duration, ionization rate of the arc, and degree of plume contraction. When the thruster is in a low input voltage state, the arc ionization rate primarily affects thrust-to-power ratio. However, when the thruster is in a high input voltage state, the degree of plume contraction primarily affects propulsion efficiency. • The effect of Energy Input on the Discharge Characteristics of the Thruster is studied. • The electrical and spectroscopic diagnosis results of the micro-cathode arc thruster are given. • Changes in energy input will affect the proportion of high-energy ions, thereby affecting the ion velocity in the plume. • The increase in ion velocity leads to an increase in the radial loss of plume energy. [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]

A kilowatt-order Hall effect thruster with a variable channel, the HET72-VC, is proposed. The discharge channel consists of an inner divergent annular segment and a cylindrical segment near the exit. A discharge comparison experiment was conducted on this thruster, in which the propellant gas is supplied along the axial direction and along the channel centerline. The results show that under the condition of gas supply along the channel centerline, both the current utilization and propellant utilization are higher, the plume divergence angle is smaller, the ion energy distribution curve moves to the high-energy portion, and the overall discharge performance, including the thrust and anode efficiency, is improved. A theoretical analysis shows that these results are attributed to the change in the ionization and acceleration characteristics caused by the different gas supply directions. The HET72-VC is demonstrated to be able to operate stably at an electric power of 2.5 kW; compared with those Hall effect thrusters with the same outer diameter or flow area of the channel, its thrust density and power density are both greatly improved. This provides a new perspective for the development of a high-power Hall effect thruster with a compact structure. [ABSTRACT FROM AUTHOR]

In this study, a particle-in-cell model of ion optics was established to simulate the changing trend of an ion beam shape over time during an ion optic start-up. This model was established to study the effect of ion beam shape change on the accel grid during ion optical start-up and to discuss the start-up strategy of ion optics. The results show that the ions at the edge of the beam have a radial velocity component toward the centerline of the ion optics owing to the electric field; this causes the ion beam to shrink gradually toward the centerline over time. Furthermore, the accel grid can be prevented from being bombarded by ions by design at the operating voltage. However, the grid may still be bombarded by ions during the low-voltage start-up process, thereby affecting its life. Thus, the ion dynamics must be considered during the start-up process. • The Start-Up Process of Ion Optics in Ion Thrusters is studied. • The density distribution and velocity distribution of ion beam during the start-up process are obtained. • The ion beam shrinks gradually toward the centerline over time during the start-up process. • The start strategy of ion optics is analyzed. [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 the near space of the low pressure environment (the pressure is 5 kPa), the effect of the dynamic permittivity of different dielectric on the performance of an ion-wind thruster with surface dielectric barrier discharge (SDBD) was investigated. The polarization intensity difference of materials with different dynamic permittivity and the space charge limiting current（SCLC）effect caused by plasma region have great influence on the performance of ion-wind thrusters. The flow velocity of the ion-wind thruster increases with the increase of the frequency, and the current increases linearly with the increase of the frequency; The frequency corresponding to the saturation flow velocity decreases with the increase of the dynamic permittivity; When the voltage and frequency are constant, with the increase of the dynamic permittivity of the dielectric, the horizontal distance between the position of the optimum wind speed and the position of the upper electrode increases; The thrust density increases with the increase of voltage amplitude; The thrust-power ratio increases first and then decreases with the voltage; The thrust density and thrust-power ratio increase with the increase of dynamic dielectric constant, and the maximum values are 1069 μN/m and 1100 μN/kW, respectively. • In the near space of the low pressure environment (the pressure is 5 kPa), the effect of the dynamic permittivity of different dielectric on the performance of an ion-wind thruster with surface dielectric barrier discharge (SDBD) was investigated. The polarization intensity difference of materials with different dynamic permittivity and the space charge limiting current（SCLC）effect caused by plasma region have great influence on the performance of ion-wind thrusters. • The flow velocity of the ion-wind thruster increases with the increase of the frequency, and the current increases linearly with the increase of the frequency; The frequency corresponding to the saturation flow velocity decreases with the increase of the dynamic permittivity. • The thrust density increases with the increase of voltage amplitude; The thrust-power ratio increases first and then decreases with the voltage; The thrust density and thrust-power ratio increase with the increase of dynamic dielectric constant, and the maximum values are 1069 μN/m and 1100 μN/kW, respectively. [ABSTRACT FROM AUTHOR]

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. • The effect of pulse frequency on the discharge characteristics of the thruster is studied. • The electrical and spectroscopic diagnosis results of the micro-cathode arc thruster are given. • The change of pulse frequency will affect the arc background pressure and thus affect the arc concentration. • The increase in arc concentration leads to an increase in the proportion of high-energy ions emitted by the cathode. [ABSTRACT FROM AUTHOR]

In this study, a high-speed camera was used to capture the ionization process of a Hall thruster with slits on the side of its discharge channel, and the change in light intensity was used to study ionization variations in the thruster channel. The light intensity was distributed along the axis, following a normal distribution. The peak position of the ionization intensity, ionization width fluctuation, and low-frequency oscillation of the Hall thruster was investigated. Experiments and simulations show that the oscillation frequency of the peak position of ionization intensity and the width of the main ionization zone are the same as the frequency of low-frequency oscillations. When discharge current increases, the peak position of ionization intensity moves towards the channel exit and the ionization width narrows during the decay of discharge current oscillations. Moreover, theoretical analyses show that the characteristics of the ionization distribution in the channel under a low-frequency-oscillation time scale are primarily governed by the ionization and supplementation of the mass flow rate. • The plasma distribution image in the inner channel of the Hall thruster is studied. • The discharge situation of the Hall thruster under low frequency oscillation is given. • The channel ionization parameters in the Hall thruster change periodically. • There is a coupling relationship between channel ionization in Hall thruster and low frequency oscillation. [ABSTRACT FROM AUTHOR]

By adjusting the relative position of the magnetic screen and the discharge channel, two types of 200 W low-power magnetically shielded Hall thrusters with three different B r e x i t / B r max ratios (the ratio of the radial magnetic field magnitude at the channel exit to the maximum radial magnetic field magnitude, taken at the channel mean diameter) using straight wall channel and chamfered wall channel geometries are designed. The discharge characteristics of the plasma under the two types of Hall thrusters are studied using the particle-in-cell (PIC) simulation, and the influence laws of the channel geometries on the thrust, specific impulse, and anode efficiency of the 200 W Hall thrusters are verified by the corresponding experimental testing. Both the results indicate that compared with the straight wall channel geometry of 200 W magnetically shielded Hall thrusters, the chamfered wall channel geometry will reduce the neutral gas density in the discharge channel, causing the propellant utilization efficiency to be lower, thus decreasing the ionization rate, ultimately reducing the performance of thruster. It explains and clarifies the reason for the dark gap phenomenon and the lower performance of the low-power magnetically shielded Hall thrusters. • The chamfered channel geometry will reduce neutral gas density, decreasing propellant utilization and ionization rate. • The straight channel geometry shows better performance than that of chamfered wall channel geometry. • When designing low-power magnetically shielded Hall thrusters, priority should be given to selecting straight channel. [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]