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Full-Text Articles in Physics

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A Robb Frederickson, Jr Dennison Dec 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A Robb Frederickson, Jr Dennison

Journal Articles

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 keV 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 ...


Low Latitude Ionospheric Disturbance Electric Field Effects Duringthe Recovery Phase Of The October 19-21, 1998 Magnetic Storm, Bela G. Fejer, J. T. Emmert Dec 2003

Low Latitude Ionospheric Disturbance Electric Field Effects Duringthe Recovery Phase Of The October 19-21, 1998 Magnetic Storm, Bela G. Fejer, J. T. Emmert

Bela G. Fejer

[1] Low-latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity. These perturbations can last for several hours after geomagnetic quieting. We use incoherent scatter radar measurements from Jicamarca and Arecibo during 19–21 October 1998 to study, for the first time, the low-latitude disturbance electric fields during the recovery phase of a large magnetic storm. On 19 October the Jicamarca data showed initially large and short-lived (time scale of about 10–20 min) upward and westward drift perturbations in the early afternoon sector, due to the penetration of strong magnetospheric electric fields probably ...


Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, Jr Dennison Dec 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, Jr 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 ...


Equatorial Counterelectrojetsduring Substorms, T. Kikuchi, K. Hashimoto, T. I. Kitamura, H. Tachihara, Bela G. Fejer Nov 2003

Equatorial Counterelectrojetsduring Substorms, T. Kikuchi, K. Hashimoto, T. I. Kitamura, H. Tachihara, Bela G. Fejer

Bela G. Fejer

[1] Equatorial counterelectrojet (CEJ) events are analyzed in association with changes in the interplanetary magnetic field (IMF), polar cap potential (PCP), and electric field measured in the equatorial ionosphere. In one event on 16 July 1995, the equatorial CEJ was observed at the afternoon dip equator during the recovery phase of the substorm when the IMF turned northward. Rapid decreases in the PCP and in the auroral electrojet occurred simultaneously with the equatorial CEJ, suggesting instantaneous equatorward penetration of the rapid decrease in the electric field associated with the region 1 field-aligned currents (R1 FACs) under the condition of a ...


Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, Jr Dennison Oct 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraft Charging, A. R. Frederickson, Jr Dennison

Conference Proceedings

Several methods have been combined to measure conductivity and charge storage in insulating spacecraft materials. In order to avoid insulator problems, the motions of conducting electrons and holes must prevent the development of large electric fields exceeding 1E5 V/cm, where problems occur in spacecraft insulators. Approximate knowledge of the electric fields is important. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination.

Classical methods to measure thin film insulator conductivity apply a constant voltage to two electrodes on the sample and measure the resulting current for tens of minutes. Under constant voltage ...


Materials Characterization At Utah State University: Facilities And Knowledgebase Of Electronic Properties Of Materials Applicable To Spacecraft Charging, Jr Dennison, C. D. Thomson, J. T. Kite, V. V. Zavyalov, Jodie Corbridge Oct 2003

Materials Characterization At Utah State University: Facilities And Knowledgebase Of Electronic Properties Of Materials Applicable To Spacecraft Charging, Jr Dennison, C. D. Thomson, J. T. Kite, V. V. Zavyalov, Jodie Corbridge

All Physics Faculty Publications

In an effort to improve the reliability and versatility of spacecraft charging models designed to assist spacecraft designers in accommodating and mitigating the harmful effects of charging on spacecraft, the NASA Space Environments and Effects (SEE) Program has funded development of facilities at Utah State University for the measurement of the electronic properties of both conducting and insulating spacecraft materials. We present here an overview of our instrumentation and capabilities, which are particularly well suited to study electron emission as related to spacecraft charging. These measurements include electron-induced secondary and backscattered yields, spectra, and angular resolved measurements as a function ...


Utilising Riometry To Observe Gravity Waves In The Sunlit Mesosphere, M. J. Jarvis, R. E. Hibbins, Michael J. Taylor, T. J. Rosenberg Oct 2003

Utilising Riometry To Observe Gravity Waves In The Sunlit Mesosphere, M. J. Jarvis, R. E. Hibbins, Michael J. Taylor, T. J. Rosenberg

All Physics Faculty Publications

The novel use of imaging riometers to observe mesospheric gravity waves is described. Imaging riometers respond to changes in the absorption of cosmic radio noise in the ionospheric D-region which enables them to detect the compression and rarefaction of the atmosphere at 90 km altitude generated by the passage of gravity waves. A considerable advantage of this method is that, unlike conventional techniques which rely on imaging faint optical emissions from the airglow layer at 87 km altitude, riometers remain operative under daylit, moonlit or cloudy conditions. This is particularly important for research into gravity wave forcing of mesospheric temperature ...


Three-Dimensional Nonlinear Evolution Ofequatorial Ionospheric Spread-F Bubbles, M. J. Keskinen, S. L. Ossakow, Bela G. Fejer Aug 2003

Three-Dimensional Nonlinear Evolution Ofequatorial Ionospheric Spread-F Bubbles, M. J. Keskinen, S. L. Ossakow, Bela G. Fejer

Bela G. Fejer

[1] Using numerical simulation techniques, we present the first study of the three-dimensional nonlinear evolution of an equatorial spread-F bubble. The background ionosphere used to initialize the bubble evolution is computed using a time-dependent first-principles equatorial plasma fountain model together with a prereversal enhancement vertical drift model. We find that finite parallel conductivity effects slow down both the linear and nonlinear bubble evolution compared to the two-dimensional evolution. In addition we find that bubble-like structures with extremely sharp density gradients can be generated off the equator at equatorial anomaly latitudes in agreement with recent observations.


An Investigation Of Gravity Wave Activity In The Low-Latitude Mesosphere: Propagation Direction And Wind Filtering, A. F. Medeiros, Michael J. Taylor, H. Takahashi, P. P. Batista, D. Gobbi Jul 2003

An Investigation Of Gravity Wave Activity In The Low-Latitude Mesosphere: Propagation Direction And Wind Filtering, A. F. Medeiros, Michael J. Taylor, H. Takahashi, P. P. Batista, D. Gobbi

All Physics Faculty Publications

An all-sky charge-coupled device imager capable of measuring wave structure in the OH, O2, and O I (557.7 nm) airglow emissions was operated at Cachoeira Paulista, Brazil (23S, 45W), for 2 years in collaboration with Utah State University, Logan. The dominant quasi-monochromatic gravity wave components investigated over a 1 year period (September 1998 to October 1999) have been extracted, and their seasonal variations have been measured. A total of 283 wave events were measured, exhibiting horizontal wavelengths from 5 to 60 km, observed periods from 5 to 35 min, and horizontal phase speeds of up to 80 m s1 ...


Validation Of Imaging Doppler Interferometer Winds Using Meteor Radar, G. O.L. Jones, C. S. Fish, W. K. Hocking, Michael J. Taylor Jul 2003

Validation Of Imaging Doppler Interferometer Winds Using Meteor Radar, G. O.L. Jones, C. S. Fish, W. K. Hocking, Michael J. Taylor

All Physics Faculty Publications

There has been some debate over the years concerning the accuracy of mesospheric wind observations made using the imaging Doppler interferometer (IDI) technique. The high potential and increasing use of IDI wind data in joint studies with spaced-antenna MF and meteor radar systems make it important to quantify the IDI results. This paper presents a novel comparison of wind measurements between a dynasonde implementation of IDI and winds derived from an all-sky meteor radar system, a widely-accepted standard for such measurements. Both radars were located at the USU Bear Lake Observatory and operated almost continuously for a four-month period. The ...


Spacecraft Charging Research, Eric Crapo May 2003

Spacecraft Charging Research, Eric Crapo

Senior Theses and Projects

No abstract provided.


Secondary Electron Emission Study Of Annealed Graphitic Amorphous Carbon, Jodie Corbridge May 2003

Secondary Electron Emission Study Of Annealed Graphitic Amorphous Carbon, Jodie Corbridge

Senior Theses and Projects

In the 1880s a curious phenomena was observed: when a ray of light, no matter how weak, hit certain metals; electrons were emitted from the surface. Called the “photoelectric effect”, this puzzle was never explained until much later. In 1905, Albert Einstein put forth one possible explanation, which is currently accepted as correct. Einstein proposed that light propagated in discrete energy packets rather than as a continuous wave. While most scientists disbelieved Einstein theory, it was later proved in detail by Robert Milikan.1 Rays of light traveling in discrete packets hit metal surfaces, depositing energy. If the energy is ...


Simulating The Doppler-Free Fluorescence Spectrum For The Potassium D1 Transitions, Paul G. Johnson, Marc R. Hammond, Vincent B. Wickwar Apr 2003

Simulating The Doppler-Free Fluorescence Spectrum For The Potassium D1 Transitions, Paul G. Johnson, Marc R. Hammond, Vincent B. Wickwar

Posters

Radiation theory (absorption, spontaneous emission, and stimulated emission) is applied to Potassium (39K and 41K) to examine details of the D1 lines, Figure 1, in the near IR at 770 nm. When examining the resonance fluorescence from two counter-propagation laser beams in a K cell, Figure 2, three prominent “Doppler-free” features—dips at the D1a and D1b resonances and spikes at their crossover frequencies—stand out superposed on the fluorescence background. They are examined with a detailed simulation, Figures 3 and 4, and compared to observations, Figure 5. Parametric studies of the Doppler-free features, Figures 6–8, indicate how to ...


Prediction Of Saturation Effects On Potassium Lidar Returns, Joel R. Drake, Vincent B. Wickwar Apr 2003

Prediction Of Saturation Effects On Potassium Lidar Returns, Joel R. Drake, Vincent B. Wickwar

Posters

The Atmospheric Lidar Observatory, on the Utah State University campus, will add a potassium lidar to its existing Rayleigh scatter system in the near future. The current system accurately measures temperatures from 40 km to 85 km in altitude.

Beginning at 80 km, a potassium layer forms due to the disintegration of meteors as they enter earth’s atmosphere. ALO plans to probe this layer using an alexandrite laser scanning a wavelength region near 770 nm, where potassium absorbs light. When the light is re-emitted, it can be measured in the same manner as scattered light in a Rayleigh lidar ...


The First 80-Hour Continuous Lidar Campaign For Simultaneous Observation Ofmesopause Region Temperature And Wind, C. Y. She, J. Sherman, Titus Yuan, B. P. Williams, K. Arnold, T. D. Kawahara, T. Li, L. F. Xu, J. D. Vance, P. Acott, D. A. Krueger Mar 2003

The First 80-Hour Continuous Lidar Campaign For Simultaneous Observation Ofmesopause Region Temperature And Wind, C. Y. She, J. Sherman, Titus Yuan, B. P. Williams, K. Arnold, T. D. Kawahara, T. Li, L. F. Xu, J. D. Vance, P. Acott, D. A. Krueger

All Physics Faculty Publications

The Colorado State Sodium lidar has been upgraded to a two-beam system capable of simultaneous measurement of mesopause region temperature and winds, day and night, weather permitting. This paper reports the initial result of the first campaign, conducted in April 2002, with a total of 145 hours of observation including an 80-hour continuous data acquisition of temperature and zonal wind. The contour plots of the continuous data set show considerable coherence and activities of upward propagating waves, with a maximum day-night difference of 15.5 m/s in zonal wind at 88 km and of 10 K in temperature at ...


A Multi-Diagnostic Investigation Of Mesospheric Bore Phenomenon, S. M. Smith, Michael J. Taylor, G. R. Swenson, C. Y. She, W. Hocking, J. Baumgardner, M. Mendillo Feb 2003

A Multi-Diagnostic Investigation Of Mesospheric Bore Phenomenon, S. M. Smith, Michael J. Taylor, G. R. Swenson, C. Y. She, W. Hocking, J. Baumgardner, M. Mendillo

All Physics Faculty Publications

Imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 November 1999 at two sites separated by over 500 km in the southwestern United States. The event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky. The waves were easily visible to the naked eye, and the entire event was observed for at least 5 1 2 hours. The event was observed using three wide-angle imaging systems located at the Boston University field station at McDonald Observatory (MDO), Fort Davis, Texas, and the Starfire Optical Range ...


Lidar Investigations Of The Middle Atmosphere Or What Is The Middle Atmosphere, What Is The Green Beam, And What Is The Red Beam?, Vincent B. Wickwar Jan 2003

Lidar Investigations Of The Middle Atmosphere Or What Is The Middle Atmosphere, What Is The Green Beam, And What Is The Red Beam?, Vincent B. Wickwar

Presentations

No abstract provided.


Climatology And Latitudinal Gradients Of Quiet-Timethermospheric Neutral Winds Over Millstone Hill From Fabry-Perot Interferometermeasurements, J. T. Emmert, Bela G. Fejer, D. P. Sipler Jan 2003

Climatology And Latitudinal Gradients Of Quiet-Timethermospheric Neutral Winds Over Millstone Hill From Fabry-Perot Interferometermeasurements, J. T. Emmert, Bela G. Fejer, D. P. Sipler

Bela G. Fejer

[1] Midlatitude nighttime thermospheric neutral winds are strongly dependent on season, solar activity, and latitude. We use an extensive database of wind measurements made during 1989–2001 by the Millstone Hill Fabry-Perot interferometer to study the detailed climatology of quiet time neutral winds near an altitude of 250 km. To facilitate the analysis of these data, we develop a local time, day-of-year, solar flux, and latitude-dependent empirical model, with the latitude dependence obtained by considering north looking and south looking observations separately. Our results show that the zonal winds are predominantly eastward after dusk and westward before dawn, with the ...


Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, Jr Dennison Jan 2003

Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, Jr Dennison

All Physics Faculty Publications

Making measurements of electron emission properties of insulators is difficult since insulators can charge either negatively or positively under charge particle bombardment. In addition, high incident energies or high fluences can result in modification of a material’s conductivity, bulk and surface charge profile, structural makeup through bond breaking and defect creation, and emission properties. We discuss here some of the charging difficulties associated with making insulator-yield measurements and review the methods used in previous studies of electron emission from insulators. We present work undertaken by our group to make consistent and accurate measurements of the electron/ion yield properties ...


Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, Jr Dennison Jan 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, Jr Dennison

All Physics Faculty Publications

Novel methods have been developed to measure conductivity and charge storage in thin film insulating spacecraft materials subjected to space radiations. For a variety of such samples, conductivity values differ by up to 104 from values based on ASTM standards. Conductivity and charge storage properties are found to be functions of prior radiation history. A highly-charged insulator emits electrons for hours (Malter Effect) after the irradiation beam is turned off. Visible light can be used to induce emission from previously charged samples with shallow traps.


Secondary Electron Production And Transport Mechanisms By Measurement Of Angle-Energyresolved Cross Sections Of Secondary And Backscattered Electrons, Jason Kite, Jr Dennison Jan 2003

Secondary Electron Production And Transport Mechanisms By Measurement Of Angle-Energyresolved Cross Sections Of Secondary And Backscattered Electrons, Jason Kite, Jr Dennison

All Physics Faculty Publications

The angle dependence of emitted electron spectra from a polycrystalline Au surface has been measured at several incident electron beam energies. The range of incident energies (~100 eV to 2500 eV) extends from below the first crossover energy, through Emax, to above the second crossover energy. The traditional distinction between secondary electrons (50 eV) is found to be inconsistent with our energy- and angle-resolved measurements. We suggest a more “natural” delineation occurs at the local minima of the emission spectra; this feature is studied as a function of incident energy and emission angle. This work is also supported by the ...


Charge Storage, Conductivity And Charge Profiles Of Insulators As Related To Spacecraft Charging, Jr Dennison, A. R. Frederickson, Prasanna Swaminathan Jan 2003

Charge Storage, Conductivity And Charge Profiles Of Insulators As Related To Spacecraft Charging, Jr Dennison, A. R. Frederickson, Prasanna Swaminathan

All Physics Faculty Publications

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal detrapping, mobility and ...


Comparison Of Classical And Charge Storage Methods For Determining Conductivity Of Thin Film Insulators, Prasanna Swaminathan, A. R. Frederickson, Jr Dennison, Alec Sim, J. Brunson, Eric Crapo Jan 2003

Comparison Of Classical And Charge Storage Methods For Determining Conductivity Of Thin Film Insulators, Prasanna Swaminathan, A. R. Frederickson, Jr Dennison, Alec Sim, J. Brunson, Eric Crapo

All Physics Faculty Publications

Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of charged particles, light, and plasma, with a metal electrode ...


Lisa Data Analysis: Doppler Demodulation, Neil J. Cornish, Shane L. Larson Jan 2003

Lisa Data Analysis: Doppler Demodulation, Neil J. Cornish, Shane L. Larson

All Physics Faculty Publications

The orbital motion of the Laser Interferometer Space Antenna (LISA) produces amplitude, phaseand frequency modulation of a gravitational wave signal. The modulations have the effect of spreading a monochromatic gravitational wave signal across a range of frequencies. The modulations encode useful information about the source location and orientation, but they also have the deleteriousaffect of spreading a signal across a wide bandwidth, thereby reducing the strength of the signalrelative to the instrument noise. We describe a simple method for removing the dominant, Doppler,component of the signal modulation. The demodulation reassembles the power from a monochromatic source into a narrow ...


Lisa Data Analysis: Source Identification And Subtraction, Neil J. Cornish, Shane L. Larson Jan 2003

Lisa Data Analysis: Source Identification And Subtraction, Neil J. Cornish, Shane L. Larson

All Physics Faculty Publications

The Laser Interferometer Space Antenna will operate as an AM-FM receiver for gravitational waves. For binary systems, the source location, orientation and orbital phase are encoded in the amplitude and frequency modulation. The same modulations spread a monochromatic signal over a range of frequencies, making it difficult to identify individual sources. We present a method for detecting and subtracting individual binary signals from a data stream with many overlapping signals.


Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, Jr Dennison, Jodie Corbridge Jan 2003

Electron Emission Properties Of Insulator Materials Pertinent To The International Space Station, C. D. Thomson, V. V. Zavyalov, Jr Dennison, Jodie Corbridge

All Physics Faculty Publications

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 ...


The Helically Reduced Wave Equation As A Symmetric Positive System, Charles G. Torre Jan 2003

The Helically Reduced Wave Equation As A Symmetric Positive System, Charles G. Torre

All Physics Faculty Publications

Motivated by the partial differential equations of mixed type that arise in the reduction of the Einstein equations by a helical Killing vector field, we consider a boundary value problem for the helically-reduced wave equation with an arbitrary source in 2+1 dimensional Minkowski spacetime. The reduced equation is a second-order partial differential equation which is elliptic inside a disk and hyperbolic outside the disk. We show that the reduced equation can be cast into symmetric-positive form. Using results from the theory of symmetric-positive differential equations, we show that this form of the helically-reduced wave equation admits unique, strong solutions ...


Lisa, Binary Stars, And The Mass Of The Graviton, Curt Cutler, William A. Hiscock, Shane L. Larson Jan 2003

Lisa, Binary Stars, And The Mass Of The Graviton, Curt Cutler, William A. Hiscock, Shane L. Larson

All Physics Faculty Publications

We extend and improve earlier estimates of the ability of the proposed LISA (Laser Interferometer Space Antenna) gravitational wave detector to place upper bounds on the graviton mass mg by comparing the arrival times of gravitational and electromagnetic signals from binary star systems. We show that the best possible limit on mg obtainable this way is ∼50 times better than the current limit set by solar system measurements. Among currently known, well-understood binaries, 4U1820-30 is the best for this purpose; LISA observations of 4U1820-30 should yield a limit ≈3-4 times better than the present solar system bound. AM ...