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

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]