Numerical study of viscosity and heat flux role in heavy species dynamics in Hall thruster discharge

Abstract

Two-dimensional with three-dimensional velocity space axisymmetric hybrid-PIC model of Hall thruster discharge called Hybrid2D has been developed. Particle-in-cell (PIC) method was used for neutrals and ions (heavy species) and fluid dynamics on magnetic-field-aligned (MFA) mesh was used for electrons. Time saving method for heavy species moments interpolation on MFA mesh was developed. The method implies using regular rectangle and irregular triangle meshes, connected to each other on preprocessing stage. Electron fluid model takes into account neither inertia terms nor viscous terms and includes electron temperature equation with heat flux term. The developed model was used to calculate all heavy species moments up to the third one in stationary case. The analysis of the viscosity and the heat flux impact on the force and energy balance has shown that for the calculated geometry of Hall thruster the viscosity and the heat flux terms have the same magnitude as the other terms and could not be omitted. Also, it was shown that the heat flux is not proportional to the temperature gradient and, consequently, the highest moments should be calculated to close the neutral fluid equation system.. At the same time, ions can only be modeled as cold non-viscous fluid when the sole aim of the modeling is the calculation of the operating parameters or distribution of the local parameters along the centerline of the discharge channel, because the magnitude of the viscosity and the temperature gradient terms is negligible in the centerline. However, when simulations’ focus is either on the radial divergence of the plume or on magnetic poles erosion, 3 components of ion temperature should be taken into consideration. The non-diagonal terms of ions’ pressure tensor have lower impact than diagonal terms. According to the study, zero heat flux condition could be used for closing the ions equation system in calculated geometry.