Numerical Investigation On Hall Thruster Discharge Characteristics Based On Particle-in-Cell Method

The numerical method based on Particle-in-Cell(PIC)is a very effective method to study Hall thruster.At present,Harbin Institute of Technology has established a corresponding numerical simulation platform.However,as the Hall thruster de velops toward the direction of high thrust and high specific impulse,the large back pressure and multivalent ionization ratio make the current simulation platform more and more unable to meet the demand.In view of the current development trend of Hall thruster,this article has further enhanced its simulation ability by considering the effects of back pressure and multivalent ionization into a numerical simulation platform.And using the enhanced numerical simulation platform to study the vacuum back pressure effect,anode temperature,multi-valence ionization characteristics.First,based on experimentally measured vacuum back pressure distribution and existing knowledge about background gas,a vacuum back pressure model was constructed by injecting vacuum background gas from the right side of the calculation boundary into the calculation area.Based on the experimentally measured polyvalent ionization cross-section parameters,MCC and NULL-Collision techniques were used to add the multivalent ionization process to the numerical simulation platform,making it capable of simulating multivalent ionization.Then,this paper analyzes the effect of back pressure on ionization acceleration characteristics,potential distribution,electron temperature distribution,and performance.The results show that the backflow of the propellent gas,which constitutes the back pressure,is mainly ionized near the exit of the channel,affecting the conductivity distribution and potential distribution inside and outside the channel,improving the ionization acceleration characteristics of the anode propellent fluid,and optimizing the working efficiency.It reduces the plume divergence angle and increases the axial velocity of the ion,making the thruster performance increase.The refore,in the thrust increment caused by the background pressure,in addition to the part of the background ionization contributes a part,it also plays an important role in the optimization of the ionization acceleration behavior of the anode propellent.In addition,the effect of back pressure on the life test results of the ground life test was studied.It was found that the back pressure affects the potential distribution,so that the energy and angle of the incident ions on the wall increase,and the flux incident on the wall decreases,enhancing the wall erosion rate with the backpressure.The lifespan of the ground life test is conservative.Next,this paper studies the effect of the anode temperature,ie,the flow rate of the working gas,at different discharge voltages on the Hall thruster discharge characteristics.The results show that the variation of thruster performance parameters with the anode temperature under different discharge voltages is in good agreement with the experimental results.Further mechanistic analysis indicates that electron temperature energy determines the diametrically opposite law of the performance of the thruster as a function of the anode temperature.When the discharge voltage is low,the electron temperature is low,and the ionization of the anode propellent is not sufficient.The change in the performance of the thruster is determined by the change of the anode temperature.When the discharge voltage is higher,the electron temperature is higher and atomic can be fully ionized.The parameter that affects the conductivity and thus the current utilization rate determines the change of the thruster performance with the change of the anode temperature.Finally,this paper studies the multivalent ionization characteristics of Hall thrusters.(1)Numerical simulation experiments were performed on a simulation platform with and without polyvalent ionization,respectively,to investigate the effect of presence or absence of multivalent ionization on Hall thruster discharge.The study found that the presence of multivalent ionization affects the distribution of potentials in the channel,such as the distribution of important parameters such as electron temperature distribution.The presence of multivalent ionization leads to an increase in discharge current,ion current,anode efficiency,and velocity impulse.(2)By constructing magnetically shielded magnetic field patterns and non-magnetically shielded magnetic field patterns,the difference in polyvalent ionization under two magnetic field patterns was studied.It was found that under the magnetic shielding magnetic field type,the electrons coming from the cathode can quickly obtain a large amount of energy because the potential drop outside the channel is large.The increase of high-energy electrons leads to the increase of multivalent ionization,which explains well the phenomenon that the ratio of multivalent ions accounts for more in the magnetic shielding mode in experiments.(3)By adjusting the flow rate of the anode propellent,the influence of the anode propellent flow on the multivalent ionization is studied.The study found that when the flow rate of the anode propellent increases,the increase of various collision rates in the channel leads to an increase in the elec trical conductivity in the channel,a decrease in the electrical potential drop in the channel,an increase in the external electrical potential drop,and an increase in the energy gained by electrons outside the channel.The increase of high-energy electrons leads to the increase of multivalent ionization,which explains well the increase in the percentage of multivalent ions that increases with the flow rate of the anode propellent.