The PIC Simulation On Characteristics Of Wall Sheath In The Discharge Channel Of Hall Thruster

Hall thruster is a kind of advanced electric propulsion device, which has important role in the field of space propulsion and has been mainly used in the attitude control, station keeping and orbit transfer of satellites and so on. It has high efficiency, high specific impulse and long lifetime. The characteristics of plasma sheath in discharge channel have important effects on its performance. Thus, further researches on the effect of plasma parameters on wall sheath characteristics in Hall thruster is essential for realizing the physical phenomenon and laws in Hall thruster, and for further optimizing operational parameters and providing theoretical direction for our country independent research high performance Hall thruster.In this paper, based on the mechanism of the interaction between plasma and wall in discharge channel of Hall thruster,2D physical model of sheath region is built according to the geometric feature of axial symmetry of discharge channel. After determined the basic calculation process and boundary conditions, the effects of magnetic field strength, electron temperature, propellants and ion incident velocity on wall sheath are investigated by using particle-in-cell method. Meanwhile, the influences of importance weights of particles and radial scale of simulation region on the stability of the sheath are analyzed. Simulation results indicate that magnetic field strength has little influence on sheath potential and secondary electron emission coefficient. While importance weights of particles are greater than106, plasma sheath oscillation is obvious and the stability of numerical results decreases. When the electron temperature is low (Te=18eV), electron number density decreases exponentially in the radial direction, the sheath potential drop and variations of electric field in the radial direction are larger, and the wall potential stays at a stable value, the stability of sheath is better. However, when the electron temperature is high (Te=36eV), the electron number density inside the sheath region is approximate to the sheath boundary, but which increases rapidly in a narrow area near the wall, sheath potential changes slowly, the sheath potential drop and variations of electric field in the radial direction are smaller, and the wall potential tends to maintain a persistent oscillation and the stability of sheath is reduced. The influence of electron temperature on electric field in the axial direction is small. With the enhance of the electron temperature, wall secondary electron emission coefficient increases in the early stage, but reduces later. Secondary electron emission coefficient increases while electron number density, sheath potential and radial electric field decrease with the augment of ion incident velocity. The influence of ion incident velocity on electric field in the axial direction is small. For argon, krypton and xenon propellant, the sheath potential and secondary electron emission coefficient reduce in turn. When the boundary conditions remain unchanged, wall potential oscillation intensifies and calculation result would not be of convergence with the increases of simulation region scale.