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Full-Text Articles in Physics
Dynamic Secondary Electron Emission In Rough Composite Materials, Leandro Olano, Maria E. Dávila, John R. Dennison, Petronilo Martín-Iglesias, Isabel Montero
Dynamic Secondary Electron Emission In Rough Composite Materials, Leandro Olano, Maria E. Dávila, John R. Dennison, Petronilo Martín-Iglesias, Isabel Montero
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The interaction of ionizing radiation with matter is of critical importance in numerous areas of science and technology like space and vacuum technology and even medicine and biotechnology. Secondary electron emission is a consequence of electron irradiation on materials. We achieve extremely low secondary electron emission yield values smaller than 0.2, even up to incident electron energies ~1 keV, due to an undocumented synergy between neighbouring metal and dielectric domains in composite samples. To investigate this experimental discovery, we propose a simple 3D model where the dielectric and metallic domains are arranged in parallel and interleaved. The proposed surface profile …
Electron Transport Models And Precision Measurements In A Constant Voltage Chamber, Justin Dekany, Alec Sim, Jerilyn Brunson, John R. Dennison
Electron Transport Models And Precision Measurements In A Constant Voltage Chamber, Justin Dekany, Alec Sim, Jerilyn Brunson, John R. Dennison
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The conductivity of the material is a key transport parameter in spacecraft charging that determines how deposited charge will redistribute throughout the system, how rapidly charge imbalances will dissipate, and what equilibrium potential will be established under given environmental conditions. As the requirements for space missions extend to new regions of space and more stringent requirements are placed on spacecraft performance, it becomes necessary to better understand the underlying conduction mechanisms that determine the dynamic response of insulators to temperature, electric field dose rate, and sample conditioning and history. This study performed detailed measurements of the transient conductivity of representative …
Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, John R. Dennison
Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, John R. Dennison
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The electron emission properties of a material subject to incident radiation flux are key parameters in determining to what equilibrium charge a spacecraft will established under given environmental conditions. However, there is a complex relation between these emission properties and the charge built up in spacecraft insulators. Complex modeling codes have been developed to predict the potential a spacecraft will adopt as a consequence of its interaction with the space plasma. These require correct models of the electron yields as a function of charge to accurately predict the both the charge build up and the equilibrium potential of spacecraft components. …
Flight Experiments On The Effects Of Contamination On Electron Emission Of Materials, John R. Dennison, Joshua L. Hodges, Jeff Duce, Amberly Evans
Flight Experiments On The Effects Of Contamination On Electron Emission Of Materials, John R. Dennison, Joshua L. Hodges, Jeff Duce, Amberly Evans
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We report on a study of the effects of prolonged exposure to the space environment and of chargeenhanced contamination on the electron emission and resistivity of spacecraft materials. The State of Utah Space Environment & Contamination Study (SUSpECS) was deployed on the International Space Station (ISS) in March 2008 onboard the MISSE-6 payload during STS-123. The Materials International Space Station Experiment (MISSE-6) program is designed to characterize the performance of candidate new space materials over the course of its ~17 month exposure to the LEO environment, with a target return date of August 2009 on STS-127. Approximately 165 samples are …
Electron-Induced Electron Yields Of Uncharged Insulating Materials, Ryan Carl Hoffmann, John R. Dennison, Jennifer Albretsen
Electron-Induced Electron Yields Of Uncharged Insulating Materials, Ryan Carl Hoffmann, John R. Dennison, Jennifer Albretsen
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This study presents electron-induced electron yield measurements from high-resistivity, high-yield materials to validate a model for the yield of uncharged insulators. These measurements are accomplished by using a low-fluence, pulsed incident electron beam and charge neutralization to minimize charge accumulation. Our measurements show large changes in total yield curves and yield decay curves, even for incident electron fluences of/mm2. We model the evolution of the yield as charge accumulates in the material in terms of electron re-capture based on the extended Chung-Everhart model of the electron emission spectrum. This model is used to explain anomalies measured in high yield ceramics, …
Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, John R. Dennison, R. C. Hoffmann, J. Abbott
Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, John R. Dennison, R. C. Hoffmann, J. Abbott
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Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is …
State Of Utah Space Environment & Contamination Study (Suspecs) Misse-6 Payload To Investigate Their Effects On Electron Emission And Resistivity Of Spacecraft Materials, John R. Dennison, L. Pearson, L. Davis, J. W. Burns, R. S. Hyde, James S. Dyer, Tina Andrus, Andrew Jay Auman, Jeff Duce, Tim Neilsen, Rob Leishman
State Of Utah Space Environment & Contamination Study (Suspecs) Misse-6 Payload To Investigate Their Effects On Electron Emission And Resistivity Of Spacecraft Materials, John R. Dennison, L. Pearson, L. Davis, J. W. Burns, R. S. Hyde, James S. Dyer, Tina Andrus, Andrew Jay Auman, Jeff Duce, Tim Neilsen, Rob Leishman
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A study of the effects of prolonged exposure to the space environment and of charge-enhanced contamination on the electron emission and resistivity of spacecraft materials, the State of Utah Space Environment & Contamination Study (SUSpECS), is planned for flight aboard the MISSE-6 payload. The Materials International Space Station Experiment (MISSE-6) program is designed to characterize the performance of candidate new space materials over the course of approximately four to eight month exposure periods on-orbit on the International Space Station, with a target flight date of mid-2006. The study is conducted by the Utah State University Materials Physics Group, in cooperation …
The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson
The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson
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Secondary electron emission is a critical contributor to the current balance in spacecraft charging. Spacecraft charging codes use a parameterized expression for the secondary electron yield δ(Eo) as a function of incident electron energy Eo. Simple three-step physics models of the electron penetration, transport and emission from a solid are typically expressed in terms of the incident electron penetration depth at normal incidence or range R(Eo ), and the mean free path of the secondary electron, λ(E). We recall classical models for the range R(Eo): a power law expression of the form b1Eon1 …
Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, John R. Dennison, Jodie Corbridge
Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, John R. Dennison, Jodie Corbridge
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We present the results of our measurements of the electron emission properties of selected insulating and conducting materials used on the International Space Station (ISS). Utah State University (USU) has performed measurements of the electron-, ion-, and photon-induced electron emission properties of conductors for a few years, and has recently extended our capabilities to measure electron yields of insulators, allowing us to significantly expand current spacecraft material charging databases. These ISS materials data are used here to illustrate our various insulator measurement techniques that include: i) Studies of electron-induced secondary and backscattered electron yield curves using pulsed, low current electron …
Instrumentation And Measurement Of Secondary Electron Emission For Spacecraft Charging, Neal Nickles, John R. Dennison
Instrumentation And Measurement Of Secondary Electron Emission For Spacecraft Charging, Neal Nickles, John R. Dennison
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Secondary electron emission is an important physical mechanism in the problem of spacecraft charging. The NASA Space Environments and Effects branch is currently revising NASA’s strategy for mitigating damage due to spacecraft charging. In an effort to substantially improve the modeling of spacecraft charging, measurements of secondary electron emission parameters are being made. The design of the apparatus needed to measure these parameters is discussed in detail. Various measurement techniques are explained and conclusions are drawn about the suitability of the final design.
Effects Of Spacecraft Potential On Secondary Electron Yields In Geosynchronous Orbit, Neal E. Nickles
Effects Of Spacecraft Potential On Secondary Electron Yields In Geosynchronous Orbit, Neal E. Nickles
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Surface charging due to interactions with the earth=s plasma is a hazard for orbiting spacecraft. Secondary electron (SE) emission is an important physical process in spacecraft charging. Current spacecraft charging models do not consider the SE energy or angular distributions and their implications for estimating the return of SE to the spacecraft. Comprehensive work on the application of SE energy and angular distributions to spacecraft charging has been published [Nickles et al., 1999] and part of that work is summarized here. The application of SE energy distributions to the case of positive charging in geosynchronous orbit is discussed and shown …
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison
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Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition—e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces can and generally do undergo significant evolution …
Electron Mean-Free Paths In The Alkali Metals, G. K. Wertheim, D. Mark Riffe, N. V. Smith, P. H. Citrin
Electron Mean-Free Paths In The Alkali Metals, G. K. Wertheim, D. Mark Riffe, N. V. Smith, P. H. Citrin
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Photoemission data in which the signal from the first atomic layer is well resolved from that of the bulk are used to determine accurately the kinetic-energy dependence of the inelastic-electron mean free path in the alkali metals. At the higher kinetic energies, the data are in very good agreement with the theory of Penn. Below about 10 eV, the mean free path in the heavier alkali metals drops markedly below the theoretical values. This is attributed to electron decay processes involving the unoccupied d bands.