Document Type

Presentation

Journal/Book Title/Conference

17th Spacecraft Charging and Technology Conference

Location

Avignon, France

Publication Date

6-2024

Abstract

Electron yield (EY) is a material attribute of central importance to understanding and modeling spacecraft charging. EY is defined as the ratio of emitted electrons to incident electrons, when irradiated with an electron beam. It depends on incident energy and is unique for each material as determined by its chemical composition, crystal structure, and electronic configurations. Dynamic surface modifications and other extrinsic factors—including surface morphology, composition, contamination, oxidation, and charging— can significantly affect EY and consequently spacecraft charging. This research proposes a “patch” model to provide a simple theoretical framework to model more complex materials comprised of any number of different types of constituent materials in terms of the EY contribution of each constituent material or feature independently. The “patch” model merges the EY contribution of each unique lateral “patch” on the surface of a material, defined as any surface feature with a unique EY value. Separating the EY contributions of individual “patches” works equally well for either different constituent materials or similar materials differentiated by extrinsic factors such as surface roughness or charging. This model can also be extended to multilayers for contamination, oxidation or coatings using established two-layer EY models for multilayer “patches”, which include linear energy transfer electron energy attenuation and backscatter reflections. These simple “patch” and “layer” models allow EY analysis of more complex materials and extrinsic factors to be modeled by separating the EY contributions of individual components, akin to parallel and series models of resistivity components. As long as the lateral dimensions of the patches are significantly greater than the energy dependent electron penetration depth—typically less than a few microns—then “edge” effects are small and the EY for the composite material is approximately equal to the normalized sum of the EY of each of the unique types of “patches” weighted by the percent of total surface area they occupy. Once the extent of the effects of extrinsic factors on EY are quantified by surface characterization measurements, it should be possible to predict how the EY of similar materials will change with modification of extrinsic features of constituent “patches”. Examples of the use of the patch model to predict the EY of complex materials in terms of electron yields of their constituents are presented.

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