Zhongxi Ning

Hall thruster with grooved walls

Axial-oriented and azimuthal-distributed grooves are formed on channel walls of a Hall thruster after the engine undergoes a long-term operation. Existing studies have demonstrated the relation between the grooves and the near-wall physics, such as sheath and electron near-wall transport. The idea to optimize the thruster performance with such grooves was also proposed. Therefore, this paper is devoted to explore the effects of wall grooves on the discharge characteristics of a Hall thruster. With experimental measurements, the variations on electron conductivity, ionization distribution, and integrated performance are obtained. The involved physical mechanisms are then analyzed and discussed. The findings help to not only better understand the working principle of Hall thruster discharge but also establish a physical fundamental for the subsequent optimization with artificial grooves.

Experimental and theoretical study on effects of magnetic field topology on near wall conductivity in a Hall thruster

An experiment has been made to investigate the effect of curved magnetic fieldtopology on near wall conductivity in the ion acceleration region of Hall thrusters. The experimental results show that the electron current due to near wall conductivity is of the minimum in the case of focused topology and increases in the cases of both less-focus and over-focus topologies. This finding cannot be explained properly by the magnetic mirroreffect, which is the one and only reported effect related to the magnetic field curvature so far. Based on the analysis of interaction between the plasma and the wall, a new physical effect is proposed. The difference of magnetic fieldtopology causes different electric potential distribution, leads to different ion flux to the wall, results in the change of sheath property and secondary electron emission, and finally affects the electron current due to near wall conductivity. This effect is further justified by the agreement between the experiment and simulation which is performed with a particle-in-cell model. Therefore, we conclude that the ion flow injection is a significant effect to near wall conductivity in the scope of curved magnetic fieldtopology besides the magnetic mirroreffect. Moreover, we find that the focus topology of magnetic field is favorable to obtain a high thruster performance from both the ion acceleration aspect and the electron conduction aspect and so is useful practically for thruster optimization.

Effects of magnetic field strength on the low frequency oscillation in Hall thrusters

In order to study the effect of magnetic field strength on low frequency oscillation in Hall thrusters, experiments were carried out with different operating parameters. Experimental results show that the effect of magnetic field strength on the low frequency oscillation changes with operating parameters. In the decline zone of magnetoampere characteristic curve, low frequency oscillation increases with the increase of magnetic field strength at low mass flow rate, while decreases with the increase of magnetic field strength at high mass flow rate. With further experiments and numerical simulations, it is found that the change of electron current at low mass flow rate and the change of ion current at high mass flow rate account for the variations of low frequency oscillation. Finally, the physical analysis is performed.

The influence of anode position and structure on cusped field thruster

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.

Experimental investigation of the effects of variable expanding channel on the performance of a low-power cusped field thruster

Due to a special magnetic field structure, the multi-cusped field thruster shows advantages of low wall erosion, low noise and high thrust density over a wide range of thrust. In this paper, expanding discharge channels are employed to make up for deficiencies on the range of thrust and plume divergence, which often emerges in conventional straight cylindrical channels. Three thruster geometries are fabricated with different expanding-angle channels, and a group of experiments are carried out to find out their influence on the performance and discharge characteristics of the thruster. A retarding potential analyzer and a Faraday probe are employed to analyze the structures of the plume in these three models. The results show that when the thrusters operate at low mass flow rate, the gradually-expanding channels exhibit lower propellant utilization and lower overall performance by amounts not exceeding 44.8% in ionization rate and 19.5% in anode efficiency, respectively. But the weakening of magnetic field...

Numerical study of influence of hydrogen backflow on krypton Hall effect thruster plasma focusing

The influence of backflow hydrogen on plasma plume focusing of a krypton Hall effect thruster is studied via a numerical simulation method. Theoretical analysis indicates that hydrogen participates in the plasma discharge process, changes the potential and ionization distribution in the thruster discharge cavity, and finally affects the plume focusing within a vacuum vessel.

Monte Carlo simulation for electron Near Wall Conductivity in Hall Thrusters

Near Wall Conductivity (NWC) is one of fundamental physical phenomena in the channel of Hall Thrusters. It has great influence on the performance parameters of Hall thruster. A Monte Carlo model on NWC is put forward in the paper. The electron is considered as test particle in the model and its initial velocity can be decided by a specific distribution function. Then electron current density due to NWC can be statistically obtained with the simulation results of a large number of electrons. Based on the Monte Carlo model, the relation between electrical field, magnetic field and electron current density due to NWC is calculated. The simulation result is well accordance with the experiment, which proves that the Monte Carlo model on NWC is valid. The Monte Carlo model on NWC provides a useful way to simulate the effect of some complicated factors lying in the real channel of Hall thruster on the electron current due to NWC. Therefore, some important physical phenomena in Hall thruster, such as sheath, channel wall material and shape, electron distribution function, magnetic field topology, have been briefly discussed in the end and the way considering these factors in Monte Carlo model is also presented. It makes possible to research the NWC phenomenon in detail.