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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]

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]

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]

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]

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 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 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]

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]