Effect Of Different Wall Materials On The Near Wall Conductivity In Hall Thruster

Hall thruster is a kind of widely used electrical propulsion device, which through ionizes propellant to convert the electrical energy into kinetic energy. Some countries have carried out a large number of researches about each aspect of hall thruster to improve the performance,due to its small volume, light quality, high precision, low thrust, etc., which is very suitable for a variety of space missions. The interaction between plasma and wall is the key point of many physical processes in the thruster channel, mainly divided into two processes: the interaction between electrons and surface and the interaction between ions and wall. The two aspects affect the distribution of electric potential in the channel, wall corrosion, etc., then affect the thrust, specific impulse and service life, etc. There is a phenomenon that the emission of secondary electrons in the interaction between electron and wall, which has a great influence to sheath dynamic feature, the near wall conductivity and thruster performance.Secondary electron emission coefficient represents the secondary electron emission feature of the channel wall materials. This paper mainly studies the effect of different wall materials on sheath dynamic feature and the near wall conductivity, on the basic of establishing secondary electron emission models of different wall materials, which can provide theoretical guidance for optimizing the thruster performance.This paper lucubrates the process of secondary electrons emission in collision between electrons and wall on the basic of the secondary electron emission model of A. I. Morozov.And modifies the secondary electron emission model of A. I. Morozov with experiment data of secondary electron emission coefficient, thereby establishes a new model which can conform the actual emission feature of different wall materials in hall thruster channel.As the transitional region between plasma mainstream region and wall, sheath has an important effect on the hall thruster performance. The experiment of sheath is very exiguity because of the difficult of sheath measurement. This paper, using the Particle-In-Cell method(2D+3V), establishes the two-dimensional sheath model and the boundary conditions, focuses on the effect on the dynamic features when chooses channel wall materials as Boron Nitride,Carborundum, Graphite and Aluminium oxide in xenon hall thruster. The result shows that the bigger secondary electron emission coefficient of wall materials, the lower electron temperature when the sheath come to be space oscillation sheath. When he sheath come to be space oscillation sheath, the azimuthal electric field in sheath has the same orders of magnitude with the axial electric field in hall thruster channel, and greater than the azimuthal electric field of time oscillation sheath.The collision between electrons and channel wall will lead to the destruction of stable hall drift motion,resulting in a axial current,which is the current of near wall conductivity.This current has an influence on the potential distribution, axial acceleration of ions in channel and the thruster performance. This paper uses the Particle-In-Cell method (2D+3V),mainly studies the effect of different wall materials on the near wall conductivity in xenon hall thruster. The result shows that when sheath is time oscillation sheath, the current of near wall conductivity is small, and will has a substantial increase in space oscillation sheath.Currently, the main hall thruster propellants is xenon and krypton, and xenon is most widely used. But for restriction by technology,xenon has a high cost of thruster,and krypton cost is relatively low. The current researches on krypton hall thruster are aimed at performance parameters, such as efficiency, specific impulse and thrust, and less attention on the near wall conductivity. This paper studies the effect of different wall materials on sheath dynamic feature and the near wall conductivity in krypton hall thruster, which can provide theoretical guidance for optimizing the thruster performance.