The Erosion Mechanism Of Ion Thruster Accelerator Grid

Electric propulsion technology has the characteristic of high specific impulse, hasbeen widely used in a variety of space missions, such as the spacecraft’s locationkeeping, providing main propulsion for aerospace system. Optical system is animportant component of an ion thruster which posses the function of focusing thedischarge plasma to ion beam and accelerate the ions to high speed and then eject fromthe accelerator aperture to produce thrust. The ion extraction process is an importantphysical process in an ion thruster operation, it affect the erosion of the accelerator gridand also affect the ion thruster’s specific impulse, thrust, efficiency. Ion thruster hasproven to be a successful system for electric propulsion. The service life of ion thrusteris primarily shortened due to grid erosion.By incorporating on IFE-PIC and Monte Carlo collision methods, athree-dimensional numerical simulation code has been developed to model the iondynamics, charge-exchange collisions, and grid erosion for ion thrusters. The studyillustrates that the backflow CEX ions bombardment downstream surface causing theerosion of the downstream surface of the accelerator grid, changes in the voltage of theaccelerator grid have a limited effect on the erosion depth of accelerator grid aperture.However, changes in the voltage of the screen grid will alter the energy of the CEX ion,which have impact on the accelerator aperture erosion. CEX ions come from upperstream, aperture region and downstream, which may cause the erosion of the acceleratoraperture. The energy of the CEX ions which come from the upper stream is much higherthan the other regions. The erosion on the accelerator grid aperture wall is primarilycaused by those charge-exchange ions originated in the upstream of the accelerator grid.In this paper, a numerical simulation code based on DSMC method also hasestablished to simulate neutral molecules distribution in the optics system. The programsimulates the neutral molecules’ movement and collision and output the densitydistribution of neutral molecules in the computational domain. The density distributionof neutral molecules gotten from the DSMC method substitute the uniformlydistribution hypothesis, and recalculate the erosion depth of the accelerator grid. Thestudy results showed that the accelerator grid impingement current get by both using theuniformity distribution hypothesis of neutral molecules and using DSMC method getthe neutral molecules’ distribution has high agreement with the measurement, but thelatter has higher agreement with the measurement.