Title

Evolution of Internal Charge Distributions of Dynamic Multilayer Materials Due to Monoenergetic Electron Fluxes

Date of Award

Spring 5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

JR Dennison

Abstract

This study presents the development of several models to predict the time evolution of the internal charge distribution of multilayer materials using known material properties and indirect measurement of the net surface potential and electrode currents. The first step in the process is to understand several important material properties related to electron interactions with the material. These include the electron penetration depth, secondary electron emission, charge transport and electrostatic discharge. By using energy dependent models of these properties, multilayer models can be developed. Using these models of properties, the net surface potential and the measurement of electrode currents can be used to extrapolate information about the internal charge distribution. A description of the Material Physic Group’s instrumentation is given along with specific instrumentation configurations unique to the given tests. Calibration and the use of the Surface Voltage Probe constructed by Joshua Hodges, parameterization of the STAIB electron gun and the measurement of the electrode currents are discussed in detail.

The theory for secondary electron yield for multilayer conductive materials is outlined for two scenarios, one with a high-density surface material and low-density substrate and another with a low-density surface material and high-density substrate. The results of the simulation show that the backscatter yield difference between the two materials affects the yield when electrons are able to backscatter from the substrate and interact with the surface layer on their traversal back out of the material. Otherwise, the surface layer material properties determine the yield, even for very thin surface layers.

The theory of multilayer charging for a multilayer dielectric is outlined for four configurations defined as surface layer deposition with grounded conductive layer, surface deposition with ungrounded conductive layer, conductive layer deposition with grounded conductive layer and conductive layer deposition with ungrounded conductive layer. The results for these tests are then outlined along with the fits given by the predictive models. The results of the tests show that knowledge of the energy-dependent electronic properties of the material, the energy of the incident electrons, and the geometry of the system are all vital to predict the outcome of the given scenario. It is shown that for multilayer materials with an ungrounded conductive layer, electrostatic discharge occurs after the material charges past the breakdown limits of the material. These results can help to design, construct, and model already deployed spacecraft to mitigate and prevent detrimental spacecraft charging effects.

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