Simulation Of Hollow Cathode Discharge Based On Comsol

Electric propulsion is a thrust device that converts electrical energy into kinetic energy.Compared with traditional chemical propulsion,it has the advantages of high specific impulse,high efficiency,and high payload ratio.Various major aerospace countries have increased their development efforts.At present,many devices have been successfully used in a series of space missions such as orbit maintenance and deep space exploration.So far,the two most studied electric propulsion devices are ion thrusters and Hall thrusters.In both thrusters,the hollow cathode serves as an electron source on the one hand and as a neutralizer on the other hand,and is a particularly important part of these two propulsion systems.In the Hall thruster,at least one cathode is required to complete the working fluid ionization and ion compensation;while in the ion thruster,these two functions are separated,at least two hollow cathodes are required,one as the electron source and the other as the middle And device.With the engineering application of electric propulsion systems,hollow cathodes as the core components of electric propulsion devices have attracted widespread attention in various countries.Therefore,it is of great significance to study the reliability and stability of the cathode.At present,the oscillation of the cathode has a non-negligible effect on the life of the cathode.Therefore,it is necessary to study the mechanism of cathode oscillation and to understand the evolution of the characteristics of plasma discharge during the cathode discharge process.The plasma parameters in the cathode plume can be obtained through probe diagnosis and spectrum diagnosis,but because the cathode structure is generally relatively small and compact,and the internal temperature of the cathode often reaches thousands of degrees Celsius,high temperature and Due to structural limitations,the plasma characteristic parameters inside the cathode are difficult to obtain through conventional experimental methods.In order to study many complex mechanisms in the cathode discharge process,the discharge parameters of the cathode are required.Therefore,the discharge of the hollow cathode needs to be simulated by means of simulation.COMSOL Multiphysics is a multiphysics coupling simulation software,suitable for simulating a variety of physical processes in science and engineering,especially the complex model of multiphysics coupling,which can well simulate the discharge process of cathodes such as plasma discharge,solid and Coupled discharge of multiple physical fields such as fluid heat transfer and gas flow,and as a relatively mature commercial software,comsol itself has a convenient graphical operation interface and a rich database,which can greatly reduce the difficulty of simulation program construction and improve the feasibility of program establishment.In fact,the software itself has a more mature means of displaying and saving results,and the convenient graphical result display improves the user's convenience.This paper builds a set of simulation software for aerospace electric propulsion hollow cathode based on comsol software.The software can be used for the macro-discharge parameters of the cathode discharge process,including voltage,current,temperature,gas pressure and micro-plasma characteristics parameters,including electron temperature,electron density,For calculation of space potential,etc.,the calculation accuracy of the software is high,and the simulation of the cathode has high reliability.First,according to the internal discharge process of the hollow cathode and its characteristic parameters,a mathematical model based on magnetohydrodynamics is constructed.Mainly considered the continuity equation,momentum equation and heat transfer equation,focusing on the analysis of the ionization process based on electron collision,and established the corresponding description equation.Due to the structure of the hollow cathode,when the magnetic field is not considered,it is suitable to use the two-dimensional axisymmetric model,so that the three-dimensional calculation results can be obtained by the two-dimensional calculation method.Therefore,based on the actual cathode geometry structure,the cathode of the cathode is constructed in the software.Dimensional model.For the simulation of cathode plasma discharge,the discharge process is mainly the movement process of various particles.The types of particles included in the model are electrons,Xe atoms,including ground and excited atoms,and monovalent Xe+ions.For Xe atoms and their excited states,the flow process caused by the density gradient is mainly described by the fluid model.For electrons and ions,they are described by the transport equation,which takes into account the density gradient,electric field,and collision effects.The model finds the particle density and energy by solving the equilibrium equation.For the non-electron particles in the discharge reaction process,consider the reflection relationship between each particle,and use the Maxwell-Stefan equation to describe the diffusion of each particle.Each particle is expressed by its mass fraction to maintain the mass conservation of the entire system.Combining these factors can simulate the process of cathode plasma discharge.Calculation of gas heat transfer in the process of cathode discharge The heating effect of the main plasma discharge process on the neutral atomic gas can automatically reflect the temperature change of the gas according to the temperature result automatically calculated by the model.Cathode solid heat transfer mainly calculates the temperature distribution on the cathode body structure.The calculation of this process is highly coupled with the calculation of the plasma discharge process,because the temperature greatly affects the thermal electron emission density on the surface of the emitter,and the thermal emission current greatly affects the plasma discharge process,which in turn affects the plasma to the wall surface.Of heating.The heat transfer process in vacuum is mainly heat conduction and heat radiation.The numerical simulation technology is relatively mature.The simulation accuracy mainly depends on the accuracy of the physical property data of the material.The source of heat received by the cathode is the heat of the electrons and ions in the plasma on the surface of the emitter Sedimentation effect.Since the software itself has a better simulation module,just set the calculation module.The simulation results are verified by real experimental results,and by simulating a cathode with the same parameters as the experimental cathode,the simulation and experiment results under the same conditions are obtained.Verification of macro parameters such as temperature,pressure,voltage,and current is relatively simple,and can be measured by conventional experimental equipment.For verification of plasma discharge,the simulation of plasma parameters in the cathode plume region is mainly measured by a probe.The result of the program verifies whether the change trend is correct in terms of magnitude and regularity.After the verification and correction of the experimental results,the reliability and accuracy of the software are improved.The software can further simulate the dynamics of the cathode when it can simulate the steady-state operation of the cathode.It is mainly used to study the oscillation effect of the cathode.In order to simulate the oscillation of the cathode with a program,the current of the cathode can be increased artificially.Method,using the program's own coupling calculation method to calculate the evolution trend of various parameters such as cathode discharge voltage,current,gas pressure,temperature,plasma density,and neutral gas density during the oscillation cycle,and the phase between each parameter and the oscillation Differences in change,find the intention of each factor to oscillate,find the core factor of influence,and determine the mechanism of cathode oscillation.Through the study of the mechanism of the cathode oscillation through this program,it will pave the way for the subsequent suppression of the oscillation of the cathode and the improvement of the stability and life of the cathode.In general,the main work to be carried out in this paper is to establish a set of effective cathodic discharge simulation software,and at the same time to study the main principles of cathode oscillation on the basis of the software.The software created in this article considers the factors in the cathode discharge process more comprehensively,the results of the coupling calculation are more accurate and have experimental verification,the software itself is simple and clear,the calculation results are relatively fast,and the simulation results are more intuitive and easy to be accepted by the reader,More convenient and easy in the process of follow-up research.And the software has high applicability.For cathodes of different powers and structures,only the geometric model and parameter input can be changed to simulate,and the reliability of the program itself is relatively high.The author hopes to inspire readers' interest in similar cathode simulation programs and methods for solving cathode problems based on the program to solve some problems encountered by cathodes that are not easily solved by traditional experimental methods during use.On the basis of the research work in this article,the author's research group will also conduct more in-depth research on other problems caused by the oscillation of the cathode,further improve the life of the cathode and the reliability of the work,and try to expand the use of the program as much as possible.Improve the calculation accuracy and accuracy of the program,simplify the use of the program,and strive to promote the promotion of the simulation method of the cathode-type plasma source.This article is mainly divided into four parts.The first part introduces the research background and motivation.After introducing the source of the topic in detail,the basic working principle and research status of the hollow cathode for electric propulsion and the simulation process of the cathode will be briefly described to facilitate the reader's understanding.The second part will describe the construction process of the cathode comsol simulation model.Reading in the order of the chapters designed by the author will help the reader understand the key issues in the construction of the cathode simulation model more clearly.The third part is the demonstration of the steady-state simulation results of the cathode,and the reliability of the simulation program is verified by comparing with the actual...