Physics Commons^™

Physics-Driven Dual-Defect Model Fits Of Voltage Step-Up To Breakdown Data In Spacecraft Polymers, Allen Andersen, Jr Dennison

Journal Articles

Overly conservative estimates of breakdown strength can increase the mass and cost of spacecraft electrostatic discharge (ESD) mitigation methods. Improved estimates of ESD likelihood in the space environment require better models of ESD distributions. The purpose of this work is to evaluate our previously proposed dual-defect model of voltage step-up-to-breakdown tests with a case study across four dielectric materials. We predicted that materials best fit by mixed Weibull distributions would exhibit better fits with the dual-defect model compared to a mean field single defect theory. Additional data for biaxially oriented polypropylene (BOPP), polyimide (PI or Kapton) from three sources, and …

Pulsed Electro-Acoustic (Pea) Measurements Of Embedded Charge Distributions, Jr Dennison, Lee H. Pearson

Conference Proceedings

Knowledge of the spatial distribution and evolution of embedded charge in thin dielectric materials has important applications in semiconductor, high-power electronic device, high-voltage DC power cable insulation, high-energy and plasma physics apparatus, and spacecraft industries. Knowing how, where, and how much charge accumulates and how it redistributes and dissipates can predict destructive charging effects. Pulsed Electro-acoustic (PEA) measurements— and two closely related methods, Pressure Wave Propagation (PWP) and Laser Intensity Modulation (LIMM)— nondestructively probe such internal charge distributions. We review the instrumentation, methods, theory and signal processing of simple PEA experiments, as well as the related PPW and LIMM methods. …

Measurements Of The Temperature Dependence Of Radiation Induced Conductivity In Polymeric Dielectrics, Jodie Corbridge Gillespie

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Radiation Induced Conductivity (RIC) is the change in conductivity of a material due to bombardment from incident high energy radiation. This study is to determine the effect of RIC and RIC's temperature dependence in polymeric dielectrics, specifically Kapton HN, Kapton E, PTFE Teflon, Tefzel, and Low Density Polyethylene (LDPE). Interest in these materials arises from applications for use in future spacecraft, specifically the James Webb Space Telescope (JWST).

One major issue in the design of JWST, as in all spacecraft, is the charging and arcing of exposed materials, resulting in fatal damage to the electronics and/or the craft itself. Particles …

Electron Energy Dependent Charging Effects Of Multilayered Dielectric Material, Gregory Wilson, Jr Dennison, Amberly Evans Jensen, Justin Dekany

Graduate Student Publications

Measurements of the charge distribution in electron-bombarded, thin-film, and multilayer dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission, and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission, and conductivity, measurements of the surface potential, displacement current, and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200-eV and 5-keV electron beams with regular 15-s pulses at …

In Situ Surface Voltage Measurements Of Dielectrics Under Electron Beam Irradiation, Joshua L. Hodges, John R. Dennison, Justin Dekany, Gregory Wilson, Amberly Evans, Alec Sim

All Physics Faculty Publications

New instrumentation has been developed for non-contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non-conductive spacecraft materials in a simulated space environment. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission analysis chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. The novel system uses two movable capacitive sensor electrodes that can be swept across the sample to measure …

Temperature Dependence Of Radiation Induced Conductivity In Insulators, Jr Dennison, Jodie Corbridge Gillespie, Joshua Hodges, Ryan C. Hoffman, J Abott, Steven Hart, Alan W. Hunt

Journal Articles

We report on measurements of Radiation Induced Conductivity (RIC) of thin film Low Density Polyethylene (LDPE) samples. RIC occurs when incident ionizing radiation deposits energy in a material and excites electrons into conduction states. RIC is calculated as the difference in sample conductivity under an incident flux and “dark current” conductivity under no incident radiation.

The primary focus of this study is the temperature dependence of the steady state RIC over a wide range of absorbed dose rates, from cryogenic temperatures to well above room temperature. The measured RIC values are compared to theoretical predictions of dose rate and temperature …

Low-Fluence Electron Yields Of Highly Insulating Materials, Ryan Hoffmann, Jr Dennison, Clint D. Thomson, Jennifer Albretson

Journal Articles

Electron-induced electron yields of high-resistivity, high-yield materials - ceramic polycrystalline aluminum oxide and the polymer polyimide (Kapton HN), - were made by using a low-fluence, pulsed incident electron beam and charge neutralization electron source to minimize charge accumulation. Large changes in energy-dependent total yield curves and yield decay curves were observed, even for incident electron fluences of <3 fC/mm². The evolution of the electron yield as charge accumulates in the material is modeled in terms of electron re-capture based on an extended Chung-Everhart model of the electron emission spectrum. This model is used to explain anomalies measured in highly insulating, …

Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B. V. Vayner, D. C. Ferguson, W. A. Degroot, C. D. Thomson, John R. Dennison, R. E. Davies

All Physics Faculty Publications

Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant …