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Articles 1 - 14 of 14
Full-Text Articles in Physics
Electron Emission And Transport Properties Database For Spacecraft Charging Models, Phil Lundgreen
Electron Emission And Transport Properties Database For Spacecraft Charging Models, Phil Lundgreen
Theses and Dissertations
Modeling the rate and likelihood of spacecraft charging during spacecraft mission is critical to determine mission length, proposed spacecraft attitude, and spacecraft design. The focus of this work is the creation and utilization of a database of secondary electron yield (SEY) measurements for a host of materials to increase accuracy in spacecraft modeling. Traditional methods of SEY data selection for input into spacecraft charging codes typically include the use of compiled materials databases incorporated in charging codes or selecting values from a specific scientific study. The SEY database allows users to select data inputs based upon the details associated with …
Studies On Secondary Electron Emission Induced Charging In Dielectric Materials: Novel Methods And Applications For Space And Plasma Technologies, Leandro Olano Garcia
Studies On Secondary Electron Emission Induced Charging In Dielectric Materials: Novel Methods And Applications For Space And Plasma Technologies, Leandro Olano Garcia
Theses and Dissertations
The interaction of ionizing radiation with matter is of critical importance in many areas of science and technology such as space and plasma technology. Secondary electron emission is a direct consequence of electron irradiation on materials. To characterize materials in terms of secondary electron emission, the secondary emission yield (SEY) and the energy spectra of the secondary electrons are key physical properties. Secondary emission yields of materials are usually too high to avoid Multipactor effect or other related phenomena in applications for space. In addition, the measurement of electron energy spectra of secondary electrons in dielectric materials is a challenge …
Secondary Electron Yield Measurements Of Carbon Nanotube Forests: Dependence On Morphology And Substrate, Brian Wood, Jordan Lee, Gregory Wilson, T. -C. Shen, Jr Dennison
Secondary Electron Yield Measurements Of Carbon Nanotube Forests: Dependence On Morphology And Substrate, Brian Wood, Jordan Lee, Gregory Wilson, T. -C. Shen, Jr Dennison
Journal Articles
Total, secondary, and backscatter electron yield data were taken with beam energies between 15 eV and 30 keV, in conjunction with energy emission data, to determine the extent of suppression of yield caused by carbon nanotube (CNT) forest coatings on substrates. CNT forests can potentially lower substrate yield due to both its inherently low-yield, low-atomic number (Z) carbon composition, and its bundled, high-aspect ratio structure. Rough surfaces, and in particular, surfaces with deep high-aspect-ratio voids, can suppress yields, as the electrons emitted from lower lying surfaces are recaptured by surface protrusions rather than escaping the near-surface region. Yields of multilayered …
Suppresion Of Electron Yield With Carbon Nanotube Forests: A Case Study, Brian Wood, Jordan Lee, Gregory Wilson, T.-C. Shen, Jr Dennison
Suppresion Of Electron Yield With Carbon Nanotube Forests: A Case Study, Brian Wood, Jordan Lee, Gregory Wilson, T.-C. Shen, Jr Dennison
Conference Proceedings
Electron emission of carbon nanotube (CNT) forests grown on silicon substrates was measured to investigate possible electron yield suppression due to the composition and morphology of CNT forests. CNT forests are vertically-oriented tubular formations of graphitic carbon grown on a substrate; these have been widely investigated for their extreme properties in optical, electrical, and mechanical aspects of physics and material sciences. CNT coatings are good candidates for yield reduction, in analogy with the near-ideal blackbody optical properties of CNT forests. Carbon with its low atomic number has an inherent low yield due to its low density of bulk electrons. Furthermore, …
Hemispherical Grid Retarding Field Analyzer Redesign For Secondary Electron Emission Studies, Greg Wilson, Jr Dennison
Hemispherical Grid Retarding Field Analyzer Redesign For Secondary Electron Emission Studies, Greg Wilson, Jr Dennison
Presentations
A redesign of the Hemispherical Grid Retarding Field Analyzer is discussed in relationship to multilayer charging models. In order to accurately extend single layer charging models to dynamic multilayer scenarios, precise measurements of electron emission as well as the net surface potential must be made. By learning from the previous design and thinking of future applications, the new instrument will greatly enhance our ability to precisely measure materials undergoing energetic electron bombardment.
Hemispherical Grid Retarding Field Analyzer Redesign For Secondary Electron Emission Studies, Greg Wilson, Jr Dennison
Hemispherical Grid Retarding Field Analyzer Redesign For Secondary Electron Emission Studies, Greg Wilson, Jr Dennison
Conference Proceedings
A redesign of the Hemispherical Grid Retarding Field Analyzer is discussed in relationship to multilayer charging models. In order to accurately extend single layer charging models to dynamic multilayer scenarios, precise measurements of electron emission as well as the net surface potential must be made. By learning from the previous design and thinking of future applications, the new instrument will greatly enhance our ability to precisely measure materials undergoing energetic electron bombardment.
Cryostat System For Spacecraft Materials Testing, Justin Dekany
Cryostat System For Spacecraft Materials Testing, Justin Dekany
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
An existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials now has extended temperature control capabilities. By incorporating a two-stage, closed-cycle helium cryostat, it is now possible to simulate the temperature typical spacecraft will experience when in orbit, ranging from < 40 K to > 450 K. The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber that can simulate diverse space environments. This vacuum chamber can simulate space environment conditions by producing the same pressure, amount of electrons, electromagnetic radiation and temperature …
Ultrahigh Vacuum Cryostat System For Extended Low Temperature Space Environment Testing, Justin Dekany, Robert H. Johnson, Gregory Wilson, Amberly Evans Jensen, Jr Dennison
Ultrahigh Vacuum Cryostat System For Extended Low Temperature Space Environment Testing, Justin Dekany, Robert H. Johnson, Gregory Wilson, Amberly Evans Jensen, Jr Dennison
Graduate Student Publications
The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new two- stage, closed-cycle helium cryostat which has an extended sample temperature range from450 K, with long-term controlled stability of
The Effects Of Surface Modification On Spacecraft Charging Parameters, Amberly Evans Jensen, Jr Dennison
The Effects Of Surface Modification On Spacecraft Charging Parameters, Amberly Evans Jensen, Jr Dennison
Graduate Student Publications
Charging of materials by incident radiation is affected by both environmental and physical conditions. Modifying a material’s physical surface will change its reflection, transmission and absorption of the incident radiation which are integrally related to the accumulation of charge and energy deposition in the material. General arguments for incident and emitted photons, electrons and ions are considered. An optical analysis of the effects of surface modification on spacecraft charging parameters on prototypical polyimide Kapton HNTM and Cu samples is presented. Samples were roughened with abrasive compounds ranging from 0.5 to 10 μm in size, comparable to the range of incident …
Low-Fluence Electron Yields Of Highly Insulating Materials, Ryan Hoffman, John R. Dennison, Clint D. Thomson, Jennifer Albresten
Low-Fluence Electron Yields Of Highly Insulating Materials, Ryan Hoffman, John R. Dennison, Clint D. Thomson, Jennifer Albresten
All Physics Faculty Publications
Electron-induced electron yields of high-resistivity high-yield materials - ceramic polycrystalline aluminum oxide and 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 the 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 recapture based on an extended Chung-Everhart model of the electron emission spectrum. This model is used to explain the anomalies measured in highly …
Evolution Of The Electron Yield Curves Of Insulators As A Function Of Impinging Electron Fluence And Energy, John R. Dennison, Alec Sim, Clint Thomson
Evolution Of The Electron Yield Curves Of Insulators As A Function Of Impinging Electron Fluence And Energy, John R. Dennison, Alec Sim, Clint Thomson
All Physics Faculty Publications
Electron emission and concomitant charge accumulation near the surface of insulators is central to understanding spacecraft charging. A study of changes in electron emission yields as a result of internal charge buildup due to electron dose is presented. Evolution of total, backscattered, and secondary yield results over a broad range of incident energies are presented for two representative insulators, Kapton and Al2O3. Reliable yield curves for uncharged insulators are measured, and quantifiable changes in yields are observed due to <100-fC/mm2 fluences. Excellent agreement with a phenomenological argument based on insulator charging predicted by the yield curve …
The Effect Of Low Energy Electron And Uv/Vis Radiation Aging On The Electron Emission Properties And Breakdown Of Thin-Film Dielectrics, John R. Dennison, C. D. Thomson, Alec Sim
The Effect Of Low Energy Electron And Uv/Vis Radiation Aging On The Electron Emission Properties And Breakdown Of Thin-Film Dielectrics, John R. Dennison, C. D. Thomson, Alec Sim
All Physics Faculty Publications
Studies of secondary and backscattered electron yield curves of thin-film dielectrics have recently been made using pulsed, low current electron beam methods to minimize insulator charging. These capabilities have allowed us to investigate the evolution of surface and internal charge profiles as a function of low energy electron (keV) pulsed-electron fluence to determine how quickly insulators charge, and how this can affect subsequent electron emission properties. We have also studied critical incident electron energies that result in electrical breakdown of insulator materials and the effect of breakdown on subsequent emission, charging and conduction. The qualitative physics of such processes in …
Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, John R. Dennison
Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, John R. Dennison
All Physics Faculty Publications
Improved experimental methods are discussed for laboratory measurement of conductivity and electric field in insulating spacecraft material intended for space radiation and plasma environments. These measurement techniques investigate the following features: 1) measurements of conductivity are up to four orders of magnitude smaller than those determined by existing standard methods. 2) Conductivity is altered as radiation accumulates and trapping states fill with electrons. 3) With intense kiloelectronvolt electron irradiation, electrons are continually emitted for hours from the irradiated surface after the irradiation ceases. 4) Charging induced by electron irradiation is strongly modified by the electron-hole pairs that the irradiation generates …
Effects Of The Evolution Of Spacecraft Surfaces On Secondary Electron Emission Andspacecraft Charging, R. E. Davies, John R. Dennison
Effects Of The Evolution Of Spacecraft Surfaces On Secondary Electron Emission Andspacecraft Charging, R. E. Davies, John R. Dennison
All Physics Faculty Publications
Spacecraft charging due to the natural plasma environment found in all orbits is known to produce many of the observed spacecraft anomalies and failures. A primary factor in adverse spacecraft charging is the secondary electron emission of differing materials on the spacecraft. Precipitating electrons and ions from the plasma to spacecraft surfaces can result in varying amounts of charge being released, depending on the secondary electron yield of the materials; this can lead to arcing between surfaces. NASA's Space and Environments Effects (SEE) program has recognized the need to improve their current materials database for modeling spacecraft charging and have …