Document Type
Presentation
Journal/Book Title/Conference
Proceedings of the 16th Spacecraft Charging Technology Conference
Location
Cocoa Beach, FL
Publication Date
4-7-2022
First Page
1
Last Page
5
Abstract
Surface conditions—including surface morphology, composition, contamination, and oxidation—can significantly affect electron yields and consequently spacecraft charging. The effects of surface roughness on electron yield are modeled in this study by considering four aspects of electron yield calculations: (i) simple models of rough surface geometry, (ii) the angular distributions of electrons emitted from various points on these surfaces, (iii) the likelihood of these emitted electrons escaping the rough surface, and (iv) the relative fractions of smooth and rough surfaces. Three simple periodic one-dimensional surface profiles were considered—namely rectangular, triangular, and sawtooth features; each surface profile was characterized by an aspect ratio of the surface feature width to the height. Two different angular emission profiles were considered for lower energy secondary electrons (a Lambertian cosine distribution) and higher energy backscattered electrons (a much narrower, energy-dependent screened Rutherford model approximating a Mott scattering cross-section which also depends on the atomic number of the material). In this initial study, only normally-incident electron profiles were considered, and any emitted electrons were assumed to be recaptured if they intersect any surface. The relative fractions of smooth and rough surfaces (which could in general have different yields for materials in these regions) were taken into account using a simple 1D "patch" model. Combining the surface profiles with the emission distributions allowed the calculation of a roughness coefficient—which predicted the effect of the surface profile on a smooth surface electron yield—for both secondary and backscattered yields for each surface geometry. Generalized predictions are presented for the reduced secondary and backscattered yields (scaled as the ratio of yields for materials in the smooth and rough fractions) as functions of aspect ratio and the fraction of the surface profile occupied by surface features. Results for backscattered electrons of different incident energies are also presented.
Recommended Citation
Trace Taylor, Matthew Robertson and JR Dennison, “Modeling the Effects of Surface Roughness on Electron Yield,” Proceedings of the 16th Spacecraft Charging Technology Conference, (Cocoa Beach FL, USA, April 4-8, 2022).