D. R. Yu

Particle-in-cell simulations for the effect of magnetic field strength on a cusped field thruster

The particle-in-cell plus Monte Carlo method is used to simulate a cusped field thruster. Three different values of magnetic field strength are simulated and convergent results are obtained successfully. The simulation results indicate that with the increase of the magnetic field strength, electron density peak tends to move in the radial direction towards the axis of the discharge channel. The central gap area of electron density is decreased due to the stronger electron confinement, which correspondingly reduces the inevitable central electron leak in the cusped field thrusters. However, it is found that the stronger confinement of electrons reduces electron density near the wall, which increases the neutral gas leak there. It is also validated that the main potential drop in the discharge channel appears near the channel exit. With the enhancement of magnetic field strength, potential drops at separatrices increase correspondingly. At the same time, several potential wells and barriers can be found near the wall, which accords well with recent theoretical and experimental results.

Effect of anisotropic non-Maxwellian electron distribution function on plasma-wall interaction in Hall thrusters

Due to the extreme plasma conditions in Hall thrusters, such as electron temperature anisotropy and non-Maxwellian electron distribution function (EDF), understanding the plasma-wall interaction is a very challenging task. This letter is attempting to study this issue with a two-dimensional particle-in-cell model. It is found that the anisotropic non-Maxwellian EDF makes the electron temperature threshold for the appearance of a spatial oscillation wall sheath much lower than the Maxwellian EDF does. Furthermore, even though the sheath potential drop in the anisotropic non-Maxwellian case is found much smaller than those in Maxwellian cases, the plasma-wall interaction becomes much weaker since the anisotropic non-Maxwellian EDF is depleted at high energies.

Volumetric erosion rate reduction of Hall thruster channel wall during ion sputtering process

The mechanisms of the volumetric erosion rate reduction of the channel wall were studied theoretically and numerically in order to explain the reasons why the volumetric erosion rate of Hall thruster channel decreases over time. The results of the theoretical analysis indicate that the variation of three sputtering conditions results from the increase in the tilt angle and the erosion depth of the channel wall erosion surface during the surface evolution process. The mass loss of the Hall thruster channel wall material is a reduction process due to which the ion flux divergent angle is smaller than the value that corresponds to the sufficient condition of the reduction process. The simulation results of the channel wall erosion process qualitatively agree well with the experimental results, and the numerical analysis of the reduction process shows that the magnitude orders of three sputtering condition variation effects on the volumetric erosion rate reduction are the same, and the reduction rate reaches its maximum value in the initial operation period when the ion radiation angle equals the optimum sputtering rate angle. This work provides theoretical fundamentals of the channel wall erosion reduction process and it can be used for the lifetime prediction and optimum design of the Hall thruster.