The effect of the oscillating sheath on the electron-wall collision frequency in Hall thruster

The effect of oscillating sheath on the near-wall conductivity is studied by using two-dimensional particle-in-cell (PIC) method. The results show that when the secondary electron emission (SEE) coefficient is greater than 1, the sheath is in the state of oscillation, in which the electron-wall collision flux periodically oscillates along the direction parallel to the wall, and the order of oscillating wavelength is the same as that of the electrostatic wavelength. The order of electron-wall collision frequency is 1-2 orders higher than the frequency of the classic shell state, and the contribution of collision frequency to the current in the channel cannot be neglected. Though the oscillating shell increases electron-wall collision frequency compared to classic shell, it prevents electron-wall collision at the same time.