Monte Carlo Raytracing Method for Calculating Secondary Electron Emission from Micro-Architected Surfaces

TL;DR

This paper introduces a novel Monte Carlo ray tracing method to accurately calculate secondary electron emission from complex micro-architected surfaces, which are designed to reduce SEE in space thruster applications.

Contribution

It extends ray tracing Monte Carlo techniques to arbitrarily complex geometries using finite element meshes from tomography images, enabling realistic SEE predictions for micro-structured surfaces.

Findings

Micro-architected surfaces can reduce SEE by up to 50%.

The method accurately models secondary electron trajectories on complex geometries.

Porosity and primary electron energy influence SEE reduction effectiveness.

Abstract

Secondary electron emission (SEE) from inner linings of plasma chambers in electric thrusters for space propulsion can have a disruptive effect on device performance and efficiency. SEE is typically calculated using elastic and inelastic electron scattering theory by way of Monte Carlo simulations of independent electron trajectories. However, in practice the method can only be applied for ideally smooth surfaces and thin films, not representative of real material surfaces. Recently, micro-architected surfaces with nanometric features have been proposed to mitigate SEE and ion-induced erosion in plasma-exposed thruster linings. In this paper, we propose an approach for calculating secondary electron yields from surfaces with arbitrarily-complex geometries using an extension of the \emph{ray tracing} Monte Carlo (RTMC) technique. We study nanofoam structures with varying porosities as representative micro-architected surfaces, and use RTMC to generate primary electron trajectories and track secondary electrons until their escape from the outer surface. Actual surfaces are represented as a discrete finite element meshes obtained from X-ray tomography images of tungsten nanofoams. At the local level, primary rays impinging into surface elements produce daughter rays of secondary electrons whose number, energies and angular characteristics are set by pre-calculated tables of SEE yields and energies from ideally-flat surfaces. We find that these micro-architected geometries can reduce SEE by up to 50\% with respect to flat surfaces depending on porosity and primary electron energy.