Three-Dimensional Particle Simulations of Ion-Optics Plasma Flow and Grid Erosion

Abstract

A fully three-dimensional computer particle simulation model for ion optics is developed. This model allows multiple apertures to be included explicitly in the simulation domain and determines the upstream sheath and downstream beam neutralization through simulations. Simulations are performed for the NSTAR ion-thruster optics, and results are compared with grid-erosion measurements obtained during NSTAR long-duration test. It is shown that the simulation not only predicts accurately all of the features in the measured erosion pattern but also gives excellent quantitative agreement with the measured erosion depth. Nomenclature E= electric eld n b , n n , n cex = number density for the beam ions, the neutrals, and the charge-exchangeions, respectively n 0 ,n 1 = discharge plasma and downstream plasma density, respectively R = depth erosion rate T e0 , T e1 = electron temperature in the upstream and the downstream plasma, respectively T w = discharge chamber wall temperature Y = sputter yielḑ D0 = Debye length in the discharge plasma ¾ cex = charge-exchangecollision cross section 8 = electric potential 8 0 , 8 1 = upstream and downstream plasma potential, respectively

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

“…It is essential in a simulation to use a sufficiently large simulation domain so that both the upstream and downstream boundary conditions can be resolved properly [10]. Moreover, it is also obvious that the boundary effects from the ion optics grid wall on the electric field must be resolved accurately in a simulation.…”

“…Existing modeling predictions of important ion optics parameters, such as the crossover limit, perveance limit, and backstreaming limit, are all based on extrapolations of single beamlet simulations, where one uses different upstream plasma conditions to represent apertures at different locations on the grid surface. Wang et al [10] presented a fully three-dimensional model which allows multiple apertures to be included in the simulation domain. However, simulations were performed only for two quarter-apertures in the center of the optics grid due to computational constrains.…”

“…The nature of plasma flow in ion optics renders particle-in-cell (PIC) [1] based models, which simulate a collisionless plasma by solving plasma particle trajectories, space charge, and the electric field self-consistently as the most appropriate approach for ion optics modeling. Numerous PIC-based ion optics simulation codes have been developed (see, for example, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and references therein). Whereas earlier studies have focused on the physics of a single beamlet, recent studies have also begun to use ion optics models to predict the behavior of entire ion optics.…”

Three‐dimensional immersed finite element methods for electric field simulation in composite materials

“…An ion optics typically consists of a screen grid and an accelerator grid, each with many apertures arranged in a hexagonal layout. A high-voltage difference (typically over 1000 V) is applied in between the two grids (typically separated by a distance of a few mm) to focus the ions through the apertures to produce the thrust [22]. Experimental research of ion optics are sometimes performed on a sub-scale gridlet consisting of a sub-set of the apertures.…”

Sensitivity Analysis of the Effects of Doubly Charged Ions on Ion Acceleration Grid Erosion

“…1) Current Ó 2012 The Japan Society for Aeronautical and Space Sciences ion engine research reflects the recent practical use of ion engines: performance enhancement, lifetime qualification of ion acceleration grid systems and neutralizers, and plume analyses. [3][4][5][6][7][8][9] Charge exchange collisions between mainstream ions and the neutral atoms represent one of the most important factors in the analysis and evaluation of grid erosion and plasma plume interaction. The ions generated by these charge exchange collisions can easily interact with the thruster and spacecraft surface because they are slow and have charges.…”