Study On Simulation Of Plasma Behaviour Inside Discharge Chamber Of Micro Ion Thruster

As the technology of small satellite boomingly develops,micro propulsion systems have became a popular field of study facing astronautic missions like deep-space exploration,attitude controlling and formation flying.Ion thruster is characterized by long time life,high specific impulse,and high efficiency,which makes research concerning micro scaling ion thrusters worthy.As a vital component of micro ion thruster,the efficiency of plasma discharge inside discharge chamber directly affects the performance of ion thruster.Thus,in this thesis,a 2D full particle model is developed,which simulates the discharge process inside a cylindrical discharge chamber.The theory of Particle-In-Cell and Monte Carlo Collision(PIC-MCC),which the simulation process of discharge is based on,is first introduced.Then the geometry of discharge chamber,the principle of selecting simulation parameters as time step,the processing of electric field and magnetic field,the processing of collision between all kinds of particles and between particles and boundaries,is thoroughly illustrated.With the completion of discharge chamber model,the disadvantage of full particle model is revealed,the simulation process is extremely slow because of the tremendous calculating quantity.Thus,measures have to be taken in order to accelerate the simulation processing.In order to accelerate the simulation,this thesis presents several common techniques that applied in PIC-MCC simulation to decrease run time,including scaling the discharge chamber,decrease the mass of heavy particles and enlarge permittivity of vacuum.The result shows that after being emitted by cathode electrons collide with background gas and then generate plasma.As the discharge process continues,the number of electrons and Xenon ions increases until discharge balance is reached.In comparison with the experimental result,plasma density in the simulation is only 5.8% smaller.And the plasma distribution is highly consistent with experimental result,which shows the reliability if this simulation model.Thirdly,the parameters that influence the efficiency of discharge are studied.The density of electrons and ions are compared in different circumstances.According to simulation results following conclusions are drawn.The size and location of cathode impact the electrons motion inside discharge chamber significantly.The oversize of cathode will lead to the electrons absorbed by cathode keeper and discharge decrease.And the cathode outlet should not be placed in somewhere that the electrons directly reach anode under the power of electric field.As the anode voltage increases the density of the plasma inside discharge chamber increases.In terms of magnetic field,the best performance is presented by 2ring-cusp magnetic field whose magnets are both located on the wall of anode,which is caused by the large size of cathode.Both the original energy of primary electrons and the discharge cathode emission current have less influence on the state of equilibrium that discharge chamber has reached than the speed of reaching equilibrium state.At last,this research calculates all kinds of energy loss inside discharge chamber of micro DC ion thruster by using global zero-dimensional discharge models.It turns out that the energy that is caused by primary electrons bombard anode is the major energy loss inside discharge chamber,which reaches almost 80% of total energy.Therefore,controlling the primary electrons energy loss to the anode wall is the key of improve the performance of discharge.In this part of research,different energy losses are calculated under different external field and cathode keeper voltage.In conclusion,increasing the duration of electrons inside the chamber in order to increase the probability of ionization collision between neutrals and electrons.