Abstract
A new, charge-conserving, energy-based, open boundary condition (BC) is developed and used to perform steady-state plasma plume simulations. This BC prevents the numerical instability, which is typically observed for kinetic simulations that employ the traditional outflow boundary, and thus allows the fully kinetic plume simulations to reach a steady-state with finite computational domain sizes. In addition to modeling a plume with colocated electron-ion sources, the BC is also applied to separated electron-ion sources which model realistic thrusters with a separate external neutralizer configuration without assuming quasi-neutrality. Domain-independence simulations performed with the new open boundary construct showed that the electric field obtained from small and large domain sizes agree within 2%. For the separated electron-ion plume, the minimum domain size required to obtain convergence is such that it must accommodate the plume until the charge density decreases by an order of magnitude. The computational cost of the electrostatic particle-in-cell simulation was found to decrease by a factor of four when the domain size was decreased by one-half.
Highlights
E LECTRIC propulsion devices emit a high-velocity ion plume to generate thrust required for the station-keeping of satellites
Notwithstanding these numerical effects of the CCE boundary condition (BC) on the z-electron velocity distribution functions (EVDFs), macroparameters, such as the electric potential and charge density variation, exhibit convergence for the 0.8-m simulation, and since ions are not reflected at the boundary, no such secondary peaks are observed for the highvelocity beam ions
We present a new, general, self-consistent, open BC for the electron particles and the electric field which was developed to perform steady-state simulations of ion thruster plasma plumes
Summary
E LECTRIC propulsion devices emit a high-velocity ion plume to generate thrust required for the station-keeping of satellites. When the beam-front of a fully kinetic thruster plume approaches the exit boundary, the electrons trapped by the positive plume core-region are lost at the beam-front due to the use of this traditional outflow BC for particles. The loss of these trapped electrons causes the self-induced electric field to accelerate the upstream electrons toward the exit boundary. We propose a new, self-consistent BC for performing fully kinetic simulations of plasma thruster plume expansions that require an open BC, which is sufficiently general, such that it permits the study of thruster plume kinetics at the steady-state using smaller computational domain sizes for both colocated and separated electron–ion configurations. Performed using the proposed open boundary construct to study PIC-DSMC simulations of the ion thruster plume [35]
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