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Raytracing Monte Carlo Method for calculating Secondary Electron Emission and Sputtering Effects on Micro-Architected Structures


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 micron-sized features have been proposed to mitigate SEE and ion-induced erosion in plasma-exposed thruster linings. In this thesis, an approach is made for calculating secondary electron yields from surfaces with arbitrarily-complex geometries using an extension of the raytracing Monte Carlo (RTMC) technique. Further, the model is extended to study the surface morphology evolution of micro-architectured foam samples due to plasma exposure. Microfoam structures are studied with varying porosities as representative micro-architected surfaces and use RTMC to generate primary electron or particle trajectories and track secondary electrons or particles 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 microfoams. 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. Depending on porosity and primary electron energy, the micro-architected geometries can reduce SEE by up to 50% with respect to flat surfaces.

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