A cusped field thruster is a kind of electric propulsion device using multi-stage cusped fields to realize plasma discharges and produce thrust. A previous study showed that plasma discharges in this thruster are non-uniform. In this work, a multi-annulus anode is used to measure the radial distribution of anode current density at different anode positions. The experimental results reveal that some electrons may reach the anode along the axis after they accelerate from the final cusp regardless of the anode positions. To further validate this idea and find out the mechanism of this central path along the axis, the central part of the anode is replaced with ceramics. This results in an increase in the total current with larger contributions at larger radii. The current oscillations also get larger. This brief letter is helpful to further understand the movement of electrons in cusped field thrusters and provide guidance on reducing the non-uniform degree of current density.
The influence of the azimuthal electron drift on anomalous erosion and the sheath profile in a stationary plasma thruster (SPT) is analysed in this article. It is found that the anomalous erosion has a self-organized structure, which is formed by the interaction between the plasma and the ceramic walls. In order to interpret the mechanism of the azimuthal erosion structure, a particle in cell (PIC) model is developed to simulate the azimuthal sheath. The results show that the electron azimuthal Hall drift due to crossed electric and magnetic field plays a key role in the azimuthal erosion evolution process. Electron Hall drift can generate an asymmetric sheath structure and induce azimuthal sheath oscillation. Furthermore, an asymmetric sheath caused by the integrated effect of the azimuthal irregular wall structure and azimuthal Hall drift will result in the azimuthal movement of ions. Based on the sheath simulated results, an erosion model is used to simulate the azimuthal erosion evolution. An asymmetric erosion profile caused by the azimuthal asymmetric ion sputtering is found.
Previous studies have shown that leak electrons in cusped field thrusters can move along the channel axis to the anode after crossing the magnetic cusp on the exit. In this paper, a onedimensional fluid model is built along two typical electron paths to study the influence of leak electrons on the discharge characteristics of a cusped field thruster, considering the electron temperature equation. It is found that the frequencies of low-frequency oscillations increase with a decrease in the proportion of leak electrons, which is related to an increase in the ion speed in the channel. Simulation results show that the position of the peak electron temperature is near the magnetic cusp on the exit and the position of the peak electron density is located downstream from the middle magnetic tip. With a decrease in the proportion of the leak electrons, the peak electron temperature and peak electron density decrease and the position of the peak electron density moves away from the exit, which is related to a decrease in the potential fall on the exit and an increase in confinement of electrons to the middle magnetic cusp.
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