Research On The Plasma Distribution In Ion Thrusterdischarge Chamber And Accelerator Grid Erosion Mechanism

Electric propulsion, also known as electric rocket, which converts the electric energy to kinetic energy. The ion thruster,one of the electric propulsion,is relatively mature.There are thousands of volts between Ion thrusters` grid so that it can accelerate ions which was ionized in the discharge to high speed.After high speed ions get out from the grid, they are neutralized by the neutralizer.Then the ion thruster get the thrust.So the grids are so important that they are the major part of the ion thruster which produce thrust.At present, there has been much research on grid corrosion, but the result was not perfect.The simulation of grid erosionon account of uniform upstream plasma density. For this assumption rationality, we simulate the discharge process of the ion thruster discharge chamber to obtain the upstream plasma density distribution. It is not reasonable to simulate the whole grid.The upstream plasma density distribution is uniform in a small range.So it can be analyzed separately for different regions of the grid.The current studies focused on the grid corrosion are mainly in conditions of normal-focus and excessive-focus.And the research focused on the accelerator erosion in under-foucus is not sufficient now. Thus,in this paper, the under-focus condition of the grid corrosion were studied.And then we study the global grid erosion with the plasma density distribution in upstream.This paper uses a two-dimensional axisymmetric program which was based on IFE-PIC algorithm and MCC algorithm to simulate the ion thruster discharge chamber ignition process. Among them, the neutral atoms distribution of the discharge chamber is simulated by a two-dimensional axisymmetric DSMC method.We got the plasma number density distribution of the upstream by simulating the discharge chamber. The results showed that the distribution of density of upstream ions is not evenly, the density of ions near the axis is larger than that of others. It decreases by the radial direction.Then, we used a three-dimensional simulation program which was also based on IFE-PIC algorithm and MCC algorithm to study the corrosion of the grid. Similarly, the neutrals distribution of the grid system use a three-dimensional DSMC numerical method to simulate the movement and collisions of neutral particles in the calculation of the region.After we got the distribution of neutrals in the calculation area, the accelerating grid`s corrosion were studied. The results showed that,in under-focused condition, the direct impact currents will became the main sources of accelerating grid`s current. And the impact currents caused by CEX ions are weakened. The erosion mechanism in under-focus condition is the same as the other conditions. CEX ions` source which result in accelerated erosion of the grid is basically the same. But the erosion depth is different. The erosion depth in under-focus condition is great than the others.Since the upstream plasma density at the the center axis is the highest, the accelerator grid erosion is the most serious.And the accelerator grid erosion depth decreases along the radial direction. The grid erosion is worst in under-focus condition.So the under- focus condition`s range should be minimized.