Effect of electron temperature anisotropy on near-wall conductivity in Hall thrusters

Abstract

The electron velocity distribution in Hall thrusters is anisotropic, which not only makes the sheath oscillate in time, but also causes the sheath to oscillate in space under the condition of low electron temperatures. The spatial oscillation sheath has a significant effect on near-wall transport current. In this Letter, the method of particle-in-cell (2D + 3 V) was adopted to simulate the effect of anisotropic electron temperatures on near-wall conductivity in a Hall thruster. Results show that the electron-wall collision frequency is within the same order in magnitude for both anisotropic and isotropic electron temperatures. The near-wall transport current produced by collisions between the electrons and the walls is much smaller than experimental measurements. However, under the condition of anisotropic electron temperatures, the non-collision transport current produced by slow electrons which reflected by the spatial oscillation sheath is much larger and closes to measurements.

Latest progress in Hall thrusters plasma modelling

“…A two-dimensional extension of the radial sheath model has been implemented by F. Zhang et al (2011Zhang et al ( , 2014 to detect spatial modulation of the sheath along the axial dimension for very large secondary electron emission. Another two-dimensional sheath model studying the effect of emissive grooved surfaces (mimicking the effect of the ion erosion on the lateral walls) have been done by Schweigert et al (2018).…”

Characteristics of wall sheath and secondary electron emission under different electron temperatures in a Hall thruster

“…[7][8][9] By improving the secondary electron emission model which was proposed by Morozov, the Harbin Institute of Technology established a 1D fluid sheath model combined with a two-dimensional (2D) particle sheath model within an insulated wall to study the influence of the electronic anisotropic temperature on the nearwall electron current, as well as the effect of a space-chargesaturated sheath on the near-wall conductivity. [10][11][12][13] In addition, the institute established a 1D fluid sheath model, analyzing the influence of the secondary electron emission coefficient on plasma sheath properties in Hall thruster channels numerically. [14][15][16] Fluid simulation, hybrid simulation and particle simulation are often used to numerically model the plasma sheath in Hall thrusters.…”