Novel electromagnetic control method of propulsion performance and discharge oscillations in a wall-less Hall thruster

The rapidly developing microsatellites have put forward new requirements of small volume and low power for propulsion systems. The Wall-Less Hall Thruster (WLHT) is proposed as a promising method to help the Hall thruster overcome the issues of wall loss and erosion when applied in microsatellites. However, the in-orbit application of WLHTs is hindered by two key issues: large beam divergence and discharge oscillations, which require further research on effective control. In this paper, a novel electromagnetic-controlled wall-less Hall thruster was developed and tested to regulate the propulsion performance including beam divergence angle, and anode oscillations. Experiments show that adjusting the coil current makes it possible to achieve high thrust performance with low anode current oscillations. According to thermalized potential theory, the performance is improved mainly due to changes in the magnetic field near the anode. At the anode voltage of 300 V and volume flow rate of 6 sccm (standard cubic centimeters per minute) using xenon gas as propellant, the electromagnetic control can increase the thrust by 10.4% (5.79 mN vs 6.39 mN) and the anode efficiency by 2.6 percentage points (19.1% vs 21.7%), and reduce the 90% plume half-angle by 14.3% (76.1° to 65.2°). In addition, the production of magnetic field via current-carrying coil can suppress the amplitude of anode current oscillations almost without reducing the thrust performance. The breathing oscillation amplitude of the anode current decreases from 37.2% to 2.6% by adjusting the coil current from +3 A to +4 A, while the thrust only decreases by 0.7% (6.39 mN vs 6.35 mN). This is mainly caused by a sudden change in the direction of the magnetic field near the cathode outlet. The performance of the proposed thruster at the anode power of 200 W is comparable to the state-of-the-art low-power wall-less Hall thrusters.