Haibin Tang

The increasing number of small satellites has resulted in greater consideration of electric propulsion (EP) as potential thruster systems. Of these, ablative pulsed plasma thrusters (APPTs) are a type of EP system that is suitable for microsatellites. They have recently attracted attention for application in small satellites due to their simple and compact system. However, from a scientific perspective, we still have limited understanding regarding APPT mechanisms such as the acceleration mechanism, plasma propagation, and associated physical phenomena. From an engineering perspective, widespread adoption can be aided by the optimization of APPTs, including improvements in the thrust efficiency, energy bank miniaturization, and a better understanding of the plasma plume characteristics and possible interactions with spacecraft. These are some issues that still remain as challenges in the research and development of APPTs. This review discusses our current understanding of the fundamental mechanisms behind APPT operation as well as some new insights and recent progress associated with APPTs. Typical characterization methods for APPTs are presented along with discussion of the operation process and relevant physical phenomena. To support an engineering perspective, we also discuss optimization approaches for APPTs such as changes in the thruster geometry, alternative propellants, and electrical circuit optimization. New insights and novel approaches resulting from the use of modern technology in APPT research are also presented, along with current understanding that attempt to tie scientific perspectives with engineering observations, such as the physical reasons behind certain performance enhancements from optimization efforts. Finally, some remaining challenging issues are also discussed.

Abstract The collisionless, steady state expansion of a warm electron, cold ion plasma thruster plume into vacuum is studied with an electrostatic particle-in-cell model and globally-consistent boundary conditions that discriminate between reflected and escaping electrons. As a proof of concept, several simulations are analyzed. Results from both two-dimensional planar and axisymmetric plasma plumes are discussed. In particular, the electron anisothermal and anisotropic behavior in the plume is recovered.

The coupling region of a Hall thruster with a hollow cathode is the region between the cathode and the thruster plume. The characteristics of plasma in that region are complicated and strongly associated with the thruster working conditions and the cathode position. In this paper, a laboratory 100 W class magnetically shielded Hall thruster was coupled with a hollow cathode. Optical imaging and electrostatic probe were employed to monitor and scan the plasma plume. Plume characteristics in the coupling region in non-self-sustained mode and self-sustained mode were compared. Evolution of the coupling plume with the cathode position was studied. Experiments show that, when turning the thruster into self-sustained mode or moving the cathode further away axially, the discharge current can be reduced by 6.4–10.6% restraining the electron current and improving ionization. In particular, when the cathode is moved further, the electron conduction near the channel walls is suppressed. The electron current is reduced by 27.4% and the ion beam current is increased by 7%. Overall, this work shows that the working mode of the thruster and the position of the cathode greatly affect the coupling plasma plume. Both play an important role in improving the utilizations of propellant and current.

Higher magnetic fields are always favoured in the magnetoplasmadynamic thruster (MPDT) due to its superior control of the plasma profile and acceleration process. This paper introduces the world's first integrated study on the 150 kW level AF-MPDT equipped with a superconductive coil. A completely new way of using superconducting magnet technology to confine plasma with high energy and extremely high temperatures is proposed. Using the PIC method of microscopic particle simulation, the plasma magnetic nozzle effect and performance of the MPDT under different magnetic-field conditions were studied. The integrated experiment used demonstrated that, in conjunction with the superconducting coil, greater homogeneity and a stronger magnetic field not only caused more even cathode ablation and improved its lifespan but also improved the performance of the MPDT (maximum thrust was 4 N at 150 kW, 0.56 T). Maximum thrust efficiency reached 76.6% and the specific impulse reached 5714 s.