Effects Of Secondary Electron Emission On The Sheath Of SPT Near The Wall

In recent years, with the development of our country aerospace and the globe, the annualrequirement of satellite is increasing sharply. And the institute of scientific research in theword focused all their attention on electric propulsion. Stationary plasma thruster is arepresentative electric propeller. The SPT is the most nature and most widely used electricalpropulsion device, and it is mainly used for station keeping and attitude control. The teams ofresearch all over the world do much research in order to improve and optimize theperformances of SPT.The stationary plasma thruster presents long chambers and ceramic wails. Sheath whichis shaped between the channel wall and plasma is basic physical problem in SPT. Becausesheath makes important influences on heat fluxes deposited at the wall, near-wall conductivity,wall erosion, plasma state inside the channel and so on. Sheath becomes the focus andpopulation of research currently.Many secondary electrons emitted from the walls when electrons with high energybombard the ceramic walls. Secondary electrons have greatly effect on SPT. In order toanalyze the sheath near the ceramic wall of SPT and the effects on thruster performances, aone-dimensional fluid mode of the sheath in the presence of secondary electron emission isformulated with the assumption that the effect of the magnetic field on the charge particlescan be neglected and the plasma is collisionless. It is discussed that SEE not only affectspotential, electric field and density of charge particles in the sheath, but also has effects onenergy flux deposited at the ceramic wall and electron temperature. Enhancement of SEEcoefficient decreases ion energy flux and increases electron energy flux and total energy fluxof charge particles deposited at the ceramic wall. These have important connections with theperformance and lifetime of SPT. Comparing between the width of channel and the thicknessof sheath, secondary electron emitted from the wall will transit the sheath and reach theopposite sheath. The effects on SPT depend mainly on the product of secondary electronemission coefficient and trapped coefficient.In order to raise the extracted current density of ions, negative ions are injected in theSPT from the cathode. In the axial electric field, negative ions are accelerated and enter thechannel. Negative ions not only restrict secondary electron emitted from the ceramic wall, butalso affect physical performance of the SPT channel.