Research On Secondary Electron Emission Model And Characteristics Of Sheath In Hall Thruster With Wall Materials

Hall thruster is a kind of advanced electric propulsion system converting electric energy into kinetic forms, which is widely applied to spacecraft attitude promoting. Position sustaining due to its high specific impulse, thrust power Plasma within the channel interacts with insulation wall materials forming a sheath nearby the wall which is small in size of Debye Length scale and hard to measure in experiment. The characters of sheath have great influence on the discharge efficiency and so on. So study the sheath with different wall materials has significance important.This paper focuses on the situation of electronic elastic reflection, improving the secondary electron emission model of silicon carbide and graphite materials. Results show that the improved curve of secondary electron emission coefficient is consistent with the experiment curve, and the electron energy distribution accords with the actual physical situation. Based on the improved secondary electron emission model, this paper establishes the two-dimensional physical model, boundary conditions, according to the characteristics of rotational symmetry and studies the properties of different wall materials (BN、 SiC、C and Al2O3) sheath by Particle-in-cell method. It shows that the four kinds of materials’ secondary electron emission coefficient increase as the electron temperature increase. Secondary electron emission coefficient of C, BN, SiC and Al2O3 increase in turn at same electron temperature. Ranging from 0 to 5 Debye Length the electron number density in sheath of BN, SiC, C and Al2O3 is kept in the same stable value; within the scale of 0 to 5 Debye Length, the electron density and sheath potential decline along the direction of the wall, and reach their minimums at wall.For the commonly used wall material of BN, the collision frequency of electrons against the wall and the near-wall conductive current distribution are studied. The results show that the collision frequency is proportional to the electron density in sheath the collision frequency increases with electron temperature rises. The near-wall conductive current peak increases with the rise of electron density or electron temperature, and its position remaining invariant.