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NASA NTRS1974

Preliminary tests of vulnerability of typical aircraft electronics to lightning-induced voltages

Tests made on two pieces of typical aircraft electronics equipment to ascertain their vulnerability to simulated lightning-induced transient voltages representative of those which might occur in flight when the aircraft is struck by lightning were conducted. The test results demonstrated that such equipment can be interfered with or damaged by transient voltages as low as 21 volts peak. Greater voltages can cause failure of semiconductor components within the equipment. The results emphasize a need for establishment of coordinated system susceptibility and component vulnerability criteria to achieve lightning protection of aerospace electrical and electronic systems.

Plumer, J. A.↗

NASA NTRS1984

Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

Boron doped silicon n+p solar cells were counterdoped with lithium by ion implanation and the resultant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacancies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Weinberg, I.↗

NASA NTRS1984

Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

Boron doped silicon n+p solar cells were counterdoped with lithium by ion implantation and the resuitant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacanies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Weinberg, I.↗

NASA NTRS1989

Measurement Of Molecular Mobilities Of Polymers

New molecular-probe technique used to measure molecular mobility of polymer. Method based on use of time-resolved electron-spin resonance (ESR) spectroscopy to monitor decay of transient nutation amplitudes from photoexcited triplet states of probe molecules with which polymer is doped. The higher molecular mobility of polymer matrix, the faster nutation amplitudes of the probe molecules decay.

Kim, Soon Sam↗

NASA NTRS2019

US Contributions to the Athena Wide Field Imager

The world’s premier X-ray astronomical observatories, Chandra and XMM-Newton, have been operating for about 20 years. The next flagship X-ray observatory launched will be ESA’s Athena mission. We discuss planned US contributions to the Athena Wide Field Imager instrument, which encompass transient source detection, background characterization and reduction, and detector electronics design and testing, in addition to scientific contributions.

David N. Burrows↗

NASA NTRS1989

Man-made transients observed by the gamma-ray spectrometer on the Solar Maximum Mission satellite

Since launch in early 1980 the gamma-ray spectrometer (GRS) on SMM has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation-belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 sec to more than 10 min. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: 511-keV annihilation-line events, particle events, and broad-band photon continuumlike events. It is found that the most likely sources of these events are reactors in earth-orbiting satellites.

Rieger, Erich↗

NASA NTRS1987

Modeling of environmentally induced transients within satellites

A technique is described that allows an estimation of possible spacecraft charging hazards. This technique, called SCREENS (spacecraft response to environments of space), utilizes the NASA charging analyzer program (NASCAP) to estimate the electrical stress locations and the charge stored in the dielectric coatings due to spacecraft encounter with a geomagnetic substorm environment. This information can then be used to determine the response of the spacecraft electrical system to a surface discharge by means of lumped element models. The coupling into the electronics is assumed to be due to magnetic linkage from the transient currents flowing as a result of the discharge transient. The behavior of a spinning spacecraft encountering a severe substorm is predicted using this technique. It is found that systems are potentially vulnerable to upset if transient signals enter through the ground lines.

Stevens, N. John↗

NASA NTRS2001

Synchronized Electronic Shutter System (SESS) for Thermal Nondestructive Evaluation

The purpose of this paper is to describe a new method for thermal nondestructive evaluation. This method uses a synchronized electronic shutter system (SESS) to remove the heat lamp's influence on the thermal data during and after flash heating. There are two main concerns when using flash heating. The first concern is during the flash when the photons are reflected back into the camera. This tends to saturate the detectors and potentially introduces unknown and uncorrectable errors when curve fitting the data to a model. To address this, an electronically controlled shutter was placed over the infrared camera lens. Before firing the flash lamps, the shutter is opened to acquire the necessary background data for offset calibration. During flash heating, the shutter is closed to prevent the photons from the high intensity flash from saturating the camera's detectors. The second concern is after the flash heating where the lamps radiate heat after firing. This residual cooling introduces an unwanted transient thermal response into the data. To remove this residual effect, a shutter was placed over the flash lamps to block the infrared heat radiating from the flash head after heating. This helped to remove the transient contribution of the flash. The flash lamp shutters were synchronized electronically with the camera shutter. Results are given comparing the use of the thermal inspection with and without the shutter system.

Zalameda, Joseph N.↗

NASA NTRS2006

The Dissipation Mechanism in Collisionless Magnetic Reconnection

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertial effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.

Hesse, Michael↗

NASA NTRS2008

The Electron Diffusion Region: Forces and Currents

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertia1 effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.

Hesse, Michael↗

NASA NTRS2009

What Turns Reconnection On and Off

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertial effect can be described as a diffusion-like term of the current density. which matches key features of electron distribution functions.

Hesse, Michael↗

NASA NTRS2009

The Electron Diffusion Region: Forces and Currents

Hesse, Michael↗

NASA NTRS1973

The chromospheric association of the metric type 3 bursts - implications concerning the acceleration of solar electrons and the active streamers

In two recent papers it was shown that the metric type 3 emission is closely related to a transient perturbation seen in absorption in the H alpha line. In addition, this perturbation sometimes triggers a flare, sometimes not. This can explain why the type 3 have a poor H alpha flare correlation rate and still are a typical flash phase emission when flare-associated. The characteristics are summarized of the new association proposed. It is assumed that 10 to 100 keV electrons are accelerated in connection with a particular kind of transient H alpha absorbing feature. For as yet undetermined reasons, this process would often, but not always, result in a more efficient acceleration coincident with the early phase of the optical flare. The possibilities that this process could lead occasionally to long lasting subrelativistic particle emissive region are explored.

Axisa, F.↗

NASA NTRS1985

DLTS analysis of radiation-induced defects in one-MeV electron irradiated germanium and Alsub0.17Gasub0.83As solar cells

The radiation-induced deep-level defects in one-MeV electron-irradiated germanium and AlxGal-xAs solar cell materials using the deep-level transient spectroscopy (DLTS) and C-V techniques were investigated. Defect and recombination parameters such as defect density and energy levels, capture cross sections and lifetimes for both electron and hole traps were determined. The germanium and AlGaAs p/n junction cells were irradiated by one-MeV electrons. The DLTS, I-V, and C-V measurements were performed on these cells. The results are summarized as follows: (1) for the irradiated germanium samples, the dominant electron trap was due to the E sub - 0.24 eV level with density around 4x10 to the 14th power 1/cu cm, independent of electron fluence, its origin is attributed to the vacancy-donor complex defect formed during the electron irradiation; (2) in the one-MeV electron irradiated Al0.17Ga0.83 as sample, two dominant electron traps with energies of Ec-0.19 and -0.29 eV were observed, the density for both electron traps remained nearly constant, independent of electron fluence. It is shown that one-MeV electron irradiation creates very few or no new deep-level traps in both the germanium and AlxGa1-xAs cells, and are suitable for fabricating the radiation-hard high efficiency multijunction solar cells for space applications.

Li, S. B.↗

NASA NTRS1990

Femtosecond optical absorption studies of nonequilibrium electronic processes in high T(c) superconductors

The results are reported of femtosecond optical transient absorption experiments performed on the superconducting compounds YBa2Cu3O(7-x) (x about 0) and Bi2Sr2Ca2Cu3O(10+delta) (delta about 0) and nonsuperconducting YBa2Cu3O(6+y) (y less than 0.4) for sample temperatures ranging from about 7 K to room temperature. Nonequilibrium heating was found to occur on a subpicosecond time scale. A distinct, dramatic increase in the relaxation time was observed for the superconducting samples as the sample temperature was lowered below the critical temperatures of the respective films. Accompanying the increase in relaxation time was an increase in the peak fractional transmissivity change. No such changes were observed for the nonsuperconducting YBCO sample.

Chwalek, J. M.↗

NASA NTRS1983

Collisionless electron shocks in electron-beam-plasma systems

One-dimensional Vlasov simulations show that when an electron beam is suddenly injected into a plasma, a fast-moving monotonic shock forms during the early stage of the transient plasma response. In the shock, the ions are nearly immobile. The shock appears to be an electrostatic electron-beam-plasma mode. The shock evolves from an initial positive potential perturbation, which is supported by an ion burst. The steepening of the perturbation into a shock is characterized by an electron-beam-plasma mode.

Singh, N.↗

NASA NTRS1965

Electro-optic crystals and their use for light modulation

Several methods of modulating a beam of light, which have been described in the literature, utilizing the influence of an electrical signal on the birefringence of certain crystals, will be reviewed. These employ optics which respond to the state of polarization of a light beam, and include intensity modulation, position modulation, and the possibility of an electrically tuned optical filter. The influence of the piezo-optic, or strain contribution to the total electro-optic response in the design of an optoelectronic device will be discussed. Current experimental work in our laboratory in which the strain contribution is separated from the direct effect will be described. The strain-free effect is measured by applying a step voltage to the crystal, and observing the initial response. The electro-optical transient response can be observed with nanosecond time resolution. An electronic sampling technique is used to extract the desired response from photon noise. The stress-free or low-frequency effect is measured similarly but at low audio frequencies. Single crystal tetragonal BaT10 3 has been investigated in detail with the result that the strain-optic contribution to the low frequency effect r_(c) = r_(33)—r_(13) is about 80% of the total, where it is only 10% in KDP and 45% in ADP. The magnitudes of the electro-optic effect, dielectric constant, and other related properties are compared for several materials potentially useful as electro-optic modulators, and some comments are made about the practical problems of building a modulator.

ELECTRO-OPTICS↗

NASA NTRS1980

Energetic particles in space

A review is presented of observations of suprathermal particles in the interplanetary medium along with new data on low energy particles from experiments aboard the ISEE spacecraft. Energy spectra of protons in the near earth atmosphere are plotted in the rest frame of the solar wind noting that at energies above 10 to the 9th eV, the galactic cosmic ray electron component has an unattenuated access into the heliosphere. Solar transient events such as flares accelerate and release energetic particles into the interplanetary medium; flare particle fluxes generate shock waves propagating past 1 AU following the event. It is concluded that the energy spectra for shock wave accelerations show a characteristic shape in accordance with the power law with a rapid steepening at high energies.

Lin, R. P.↗