Simulation On Effect Of Secondary Electron Emission On The Sheath In SPT Chamber

Electric propulsions have become an important potential tool to provide propulsion in deep space exploration,especially the stationary plasma thruster(SPT).But,at present,there are still a great deal difficult problems in the investigation of it.The interaction between the bulk plasma and the walls is one of them.In this work,we consider the effect of secondary electron emission from the walls to the plasma sheath in SPTs from two aspects:The effect of the count-streaming SEE to the plasma sheath in the stable state both in 1-D fluid and 2-D PIC models;The instability in the plasma sheath resulted from the SEE from the walls.In the second part,a one-dimensional slab model of the plasma sheath in the stationary plasma thruster chamber is developed.It is considered that secondary electrons emitted from ceramic walls are partially trapped by the bulk plasma in the SPT chamber;some secondary electrons drift across the sheath where they are generated and the bulk and move towards the opposite sheath.The results indicate that::1.Both the SEE coefficient and trapping coefficient have a significant impact not only on the distributions of both electrons and ions of the SPT sheath but also on the energy flux loss to the SPT wall.2.When the trapping coefficient increases,the energy flux of electrons deposited to the walls will increase whereas that of ions will decrease.3.The critical electron temperature will decrease greatly with the increase of the trapping coefficient.In the third part,we found a 2-D PIC model of hall thruster chamber.We get the distribution of electron energy in sheaths and the distribution of density of electric current in the chamber.Then we also discuss the effect of electric field and magnetic field on the density of electric current,and the effect of annular chamber is proved.In the last part,the sheath instability discussed appears to be due to the nonlinear dependence of the total electron current in the sheath on the plasma potential relative to the walls.This nonlinear dependence is implemented via a mechanism involving:1.Oscillation of the energy of secondary electron beams along their trajectory in crossed electric and magnetic fields 2.Corresponding medication of intensity of SEE produced by these beams them- selves.We got the conclusion that the instability lasts for about the time of electron flight between the walls.