Condensed Matter Physics Commons^™

Radiation Induced Conductivity Of Peek: Effects Of Temperature And Total Ionizing Dose, Joshua Boman, Brian Wood, Jordan Lee, Jr Dennison, Kim M. Aaron, Wousik Kim

Conference Proceedings

Radiation induced conductivity (RIC) plays a critical role in space charge dissipation with insulating materials used in spacecraft. Ionizing radiation present in harsh space plasma environments deposits energy into materials via inelastic scatter, exciting electrons into the conduction band without depositing charge for penetration radiation. RIC is expected to be affected by temperature and total ionizing dose (TID); temperature primarily affects the rate of promotion of electrons in localized trap states within the band gap to the conduction band, while TID can create additional traps states thereby increasing trap density and reducing mean trap separation.

RIC was measured in a …

Temperature Dependent Radiation Induced Conductivity Of Polymeric Spacecraft Materials, Jodie Corbridge Gillespie, Jr Dennison

Conference Proceedings

Temperature dependent radiation induced conductivity (RIC) data applicable to conditions experienced by spacecraft are presented for low density polyethylene (LDPE) and poylimide (PI, Kapton^HN, along with summaries for five other common polymeric spacecraft mateials: polyimide (PI; Kapton HN^TM, and Kapton E^TM), polytetraflouroethylene (PTFE; Teflon^TM), expanded PTFE (ePTFE), ethylene-tetrafluoroethylene and (ETFE; Tefzel^TM). Data were measured over approximately 105 K to 330 K and incident dose rates, D, of 10^-4 Gy/s to 10^-1Gy/s. Theoretical expressions proposed by Rose/Fowler/Vissenberg predict equilibrium RIC behavior according to a general expression σ …

Time-Dependent Behavior Of Radiation Induced Conductivity In Polymers, Tyler Heggenes, Jenny R. Whiteley, Jodie Corbridge Gillespie, Joshua Boman, Jr Dennison

Conference Proceedings

Ionizing radiation can induce conductivity in polymers via inelastic scattering which imparts energy to electrons in the valence band and trapped states, exciting them into the conduction band without depositing charge into the material. This radiation-induced conductivity (RIC) can impact space charge dissipation within highly insulating materials used in spacecraft in harsh space plasma environments. Previous USU research analyzed only the equilibrium portions of an extensive RIC database for polymeric materials, including Kapton HN^TM. This confirmed that equilibrium RIC follows a standard theoretical model that is temperature and dose-dependent. The current study provides a new analysis of RIC's …

Analysis Of The Effects Of Surface Modifications And Other Extrinsic Factors On Electron Yield With A “Patch” Model, Matthew Robertson, Christopher Vega, Trace Taylor, Jr Dennison

Conference Proceedings

Electron yield (EY) is a material property of central importance to understanding and modeling spacecraft charging. It depends on incident energy and is unique for each material. Dynamic surface modifications and other extrinsic factors—including composition, surface morphology, 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 extrinsic factor. The “patch” model merges the unique EY curve contribution of each …

Effects Of Differing Radiation Methods On Charge Transport In Polymers, Zachary J. Gibson, Jr Dennison, Virginie Griseri

Conference Proceedings

Spacecraft charging issues are understood and mitigated through an understanding of material properties. Material properties are dynamic in the harsh environment of space. Approximations must be made to simulate the space environment in the laboratory. This paper reports on the investigation of the approximation that energy deposition causes the same aging effects in the materials regardless of the radiation source. Samples of polytetrafluoroethylene (PTFE) and polyether-etherketone (PEEK) were irradiated with x-rays, γ-rays, or electrons at total ionizing dose (TID) of either 2 x 10⁴, 2 x 10⁵, or 2 x 10⁶ rad. Charge was then …

Modeling The Effects Of Surface Roughness On Electron Yield, Trace Taylor, Matthew Robertson, Jr Dennison

Conference Proceedings

Surface conditions—including surface morphology, composition, contamination, and oxidation—can significantly affect electron yields and consequently spacecraft charging. The effects of surface roughness on electron yield are modeled in this study by considering four aspects of electron yield calculations: (i) simple models of rough surface geometry, (ii) the angular distributions of electrons emitted from various points on these surfaces, (iii) the likelihood of these emitted electrons escaping the rough surface, and (iv) the relative fractions of smooth and rough surfaces. Three simple periodic one-dimensional surface profiles were considered—namely rectangular, triangular, and sawtooth features; each surface profile was characterized by an aspect ratio …

Laboratory Simulations Of Simultaneous Reduced Gravity And Ionizing Radiation Environments, Achal Duhoon, Jr Dennison

Conference Proceedings

A novel system has been developed to simulate the combined effects of reduced gravity and ionizing radiation present during spaceflight on biological and particulate samples. The miniature rotary cell culture system (mRCCS) was designed to synchronously rotate up to five independent vessels containing particulate samples suspended in fluid media, constructed using radiation tolerant, biocompatible, and vacuum compatible materials. Reduced gravity conditions were achieved when particles (e.g., 200 µm polystyrene microcarrier beads with or without adhered cell clusters) were suspended inside the vessels moving near terminal velocity in viscous fluid media with densities matched to the suspended …

Electron Yield Measurements Of Multilayer Conductive Materials, Gregory Wilson, Matthew Robertson, Jordan Lee, Jr Dennison

Conference Proceedings

As energetic electrons interact with the surface of materials, they impart energy throughout the material. If the energy exchange is near the surface, secondary electrons within the material can be excited and emitted. It is also possible for the incident primary electron to undergo a quasi-elastic collision within the material, wherein the electron is backscattered and emitted from the surface. As the backscattered electron is leaving the material, it can continue to impart energy to the material, potentially exciting more secondary electrons as it approaches the surface on the way back out.

This process of imparting energy and charge to …

Strategies For Determining Electron Yield Material Parameters For Spacecraft Charge Modeling, Phil Lundgreen, Jr Dennison

Conference Proceedings

Modeling of space plasma environment-induced anomalies requires knowledge of:

• Environment and impinging fluxes during spacecraft orbits, which are mission specific and can be incorporated through environmental models and databases.
• Satellite geometry and orientation in the space environment, accomplished through such charging codes as NASCAP-2K, SPENVIS, or MUSCAT.
• Materials used in spacecraft construction, from the specific spacecraft design.
• Relevant materials properties characterizing the interaction of the materials with the environment and how these properties may change with exposure to the space environment.

A reliable, comprehensive database of spacecraft materials and the characterization of those materials is being created in the form …

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, …

Influence Of Vibrationally-Induced Structural Changes On Carbon Nanotube Forests Suppression Of Electron Yield, Jordan Lee, Brian Wood, Gregory Wilson, T.-C. Shen, Jr Dennison

Conference Proceedings

Carbon nanotube (CNT) forest coatings have been found to lower electron yield from material surfaces. The suppressed yields have been attributed to both the lower inherent yields of low-atomic number carbon and the enhanced electron recapture resulting from the morphology of the carbon layer. To explore the relative contributions of these two causes of yield suppression, tests have been made on CNT forest-coated conducting substrate samples subjected to vibrationally-induced changes of the coating structure. The extent of vibrationally-induced structural changes—due, for example, to shear-force conditions during space-vehicle transit—are of interest, as CNT have been a frequent topic of scientific curiosity …

Wireless Antenna Detection Of Electrostatic Discharge Events, Allen Andersen, Jr Dennison

Conference Proceedings

Wireless intra-spacecraft communication technology is being developed as a weight-saving and design-simplifying measure for signal transfer on space missions. One consideration for this new technology is its interaction with space-environment induced electrostatic discharges (ESD). The short time scales of spacecraft ESD events results in broad frequency signals that can interact with wireless antennae. These interactions present a source of signal noise. However, they may also present a possibility of in-flight wireless ESD monitoring.

We present laboratory measurements of arcing on common spacecraft insulators using commercially available single band 2.4 GHz and dual band 2.4/5.8 GHz Wi-Fi antennas. These wireless detections …

Secondary Electron Yield Measurements Of Carbon Nanotube Forests: Dependence On Morphology And Substrate, Brian Wood, Justin Christensen, Gregory Wilson, T. -C. Shen, Jr Dennison

Conference Proceedings

No abstract provided.

Effects Of Sample Adhesives Acoustic Properties On Spatial Resolution Of Pulsed Electroacoustic Measurements, Zachary Gibson, Jr Dennison, Lee Pearson, Erick Griffiths, Anthony Pearson, Virginie Griseri

Conference Proceedings

No abstract provided.

Incorporating Electron Range Approximations Into Secondary Electron Emission Models, Gregory Wilson

Conference Proceedings

No abstract provided.

Electron Range Computational Tool For Arbitrary Materials Over A Wide Energy Range, Gregory Wilson, Jr Dennison, Anne C. Starley

Conference Proceedings

No abstract provided.

Time-Evolved Constant Voltage Conductivity Polymeric Materials, Brian Wood, Jr Dennison, David King

Conference Proceedings

No abstract provided.

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.

Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed, Leandro Olano, Isabel Montero, María E. Dávila, A. Jacas, M. A. Rodriguez, Jr Dennison

Conference Proceedings

Secondary Emission Yield (SEY) of dielectric materials is of great importance for prediction and testing of the Multipaction discharge in RF components for space applications. An atypical behavior of the SEY of coatings composed by a mixture of conductor and dielectric microparticles was reported and modeled in [1]; in this original model, the interactions between dielectric and conductor particles were not taken into account, but an effective action of the surface voltage generated within the sample was included. The aim of the present contribution is to more accurately model the effect the electric fields between dielectric and conductor particles have …

Hemispherical Grid Retarding Field Analyzer Redesign For Secondary Electron Emission Studies, Gregory Wilson

Conference Proceedings

No abstract provided.

Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed Coatings, Leandro Olano, Maria E. Davila, A. Jacas, M A. Rodriguez, Jr Dennison

Conference Proceedings

No abstract provided.

Instrumentation Enhancements For Electron Yield Measurements Of Extremely Low-Conductivity High-Yield Dielectrics, Justin Christensen, Gregory Wilson, Jr Dennison

Conference Proceedings

Electron yield, a material dependent property which describes how it will charge under incident electron irradiation of a given energy, is defined as the number of electrons emitted from a material per incident electron. While very important for spacecraft charging modelling, the measurement of electron yield for insulating materials is very challenging because insulators quickly charge up under electron irradiation, thereby modifying the yield measurements.

Improved techniques have been implemented to reduce charging with each yield measurement, as well as to neutralize acquired charge between measurements. The goal is to determine the “intrinsic yield” (yield of uncharged insulator). New analysis …

Dependence Of Electrostatic Field Strength On Voltage Ramp Rate For Spacecraft Materials, Krysta Moser, Allen Andersen, Jr Dennison

Conference Proceedings

This work investigated the dependence of electrostatic field strength for spacecraft materials on voltage ramp rate, by applying an increasing electrostatic field until electrostatic breakdown occurred.

Tests on the polymeric material Kapton ETM found that at ramp rates two or three orders of magnitude lower than the maximum recommended rate, FESD was lower than at rapid rates by a factor or two or more this suggests that tabulated values of FESD which have been used by the spacecraft charging community can substantially overestimate FESD in common slowly evolving spacecraft situations. Similar measurements on other polymeric materials have been performed to …

Absolute Electron Emission Calibration: Round Eobin Tests Of Au And Graphite, Jr Dennison, Justin Christensen, Justin Dekany, Clint Thomson, Neal Nickles, Robert E. Davies, Mohamed Belhaj, Kazuhiro Toyoda, Kazutaka Kawasaki, Isabel Montero, Maria E. Dávil, Leandro Olano, Luis Galán

Conference Proceedings

This study presents a round robin comparison of absolute electron yields of conducting and insulating materials performed in four international laboratories. Measurements are reported for two standard elemental conducting samples with reproducible sample preparation for Au and highly oriented pyrolytic graphite (HOPG). The primary objectives of the study were to determine the consistency and uncertainties of these absolute yields measurements, and to investigate the effects of the similarities and differences of the diverse facilities. In this initial round robin study, HOPG total electron yield results were found to be more reproducible than those for Au. Surface contamination significantly affected the …

Temporal And Spatial Correlations In Electron-Induced Arcs Of Adjacent Dielectric Islands, Justin Christensen, Jr Dennison, Justin Dekany

Conference Proceedings

This study investigated coincidence behaviour of a common form of electron-induced light emission [6]. These very short duration(

Pulsed Electroacoustic System Development For Volume Charge Distribution Measurement In Thin Dielectric Films, Lee H. Pearson, Jr Dennison, Erick W. Griffiths, Anthony C. Pearson

Conference Proceedings

This paper discusses an effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate state-of-the-art hardware and improved signal processing and modeling to characterize embedded charge distributions in thin dielectric films. Objectives in developing this system include: (1) improved spatial resolution, while maintaining reasonable temporal resolution; (2) improved signal processing tools for increased signal/noise ratios; (3) integrated PEA modeling tools; and (4) integrated environmental controls. We emphasize system improvements required to achieve high spatial resolution for in vacuo measurements of thin dielectrics charged using electron beam injection, which are most applicable for spacecraft charging tests. PEA measurement systems …

Extremely Low Secondary Electron Emission From Metal/Dielectricparticulate Coatings, Isabel Montero, L Aguilera, Leandro Olano, María E. Dávila, V. Nistor, L. Galán, Jr Dennison, Gregory Wilson

Conference Proceedings

We have studied the SEY behaviour of a particulate coating composed of a mixture of a metal (aluminum) in solid state contact with a particulate dielectric material (polyimide thermosetting resin). Surface charging, roughness, and volume fraction are utilized as the main parameters to characterize the electron emission behaviour. Apart from the important role played by surface composition in the SEY, the influence of the dielectric volume fraction has demonstrated to be critical to achieve a significant reduction of SEY. it was found that E1 of the particulate sample increased with increasing dielectric volume fraction. An extremely high first crossover energy, …

Synergistic Models Of Electron Emission And Transport Measurements Of Disordered Sio2, Jr Dennison, Jodie Corbridge Gillespie, Allen Andersen, Amberly Evans Jensen, Gregory Wilson, Justin Dekany, Alec Sim, Ryan C. Hoffmann

Conference Proceedings

An important way for the spacecraft charging community to address the expanding necessity for extensive characterization of electron emission and transport properties of materials is to expand the role of more fundamental materials physics. This includes the development of unifying theoretical models of the charge transport equations based on the creation, distribution, and occupancy of defect densities of states. Models that emphasize the synergistic relation between fitting parameters for diverse measurements can also lead to a better understanding of materials and facilitate solutions to spacecraft charging issues. As an example of this approach, we present results of many different measurements …

Pea System Modeling And Signal Processing For Measurement Of Volume Charge Distributions In Thin Dielectric Films, Lee H. Pearson, Jr Dennison, Erick W. Griffiths, A C. Pearson

Conference Proceedings

This paper discusses an effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate (1) improved signal processing tools for increased signal/noise ratios; and (2) integrated PEA modeling tools. In addition, we emphasize state-of-the-art system electronic components, integrated environmental controls, and sensor improvements required to achieve high spatial resolution while maintaining reasonable temporal resolution for both ambient and in vacuo measurements of thin dielectrics charged using electron beam injection, which are most applicable for spacecraft charging tests. PEA measurement systems provide an important tool to investigate the spatial extent and dynamic evolution of such embedded charge distributions in …

Perspectives On The Distributions Of Esd Breakdowns For Spacecraft Charging Applications, Allen Andersen, Krysta Moser, Jr Dennison

Conference Proceedings

Electrostatic discharge (ESD) continues to pose significant risks to space missions despite decades of intense study. We emphasize here the advantages to spacecraft designers and modelers from considering the stochastic distributions of breakdown and how it can be affected by factors including spacecraft environment conditions, design geometries, material temperature, material purity, charging history, and appropriate timescales. Spacecraft charging models and spacecraft designs typically rely on tabulated values or ranges of breakdown strength, often based on cursory measurements with little or no experimental detail. Depending on the timescales and history of environmental and orbital changes or durations of specific missions, it …