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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The simulated space proton environment for radiation effects on Space Telescope Imaging Spectrograph (STIS)

The space telescope imaging spectrograph (STIS) is a second generation instrument planned for the Hubble Space Telescope (HST) which is currently in orbit. Candidate glasses and other transmitting materials are being considered for order sorters, in-flight calibration filters, detector windows, and calibration lamps. The glasses for in-flight calibration filters showed significant drop in UV transmission, but can probably still be used on STIS. The addressed topics include the Hubble radiation environment, simulation of orbital exposure at Harvard Cyclotron Laboratory, measurement of spectral transmission, and comments on individual samples.

Becher, Jacob↗
NASA NTRS1981

Saturation and energy-conversion efficiency of auroral kilometric radiation

A quasi-linear theory is used to study the saturation level of the auroral kilometric radiation. The investigation is based on the assumption that the emission is due to a cyclotron maser instability as suggested by Wu and Lee and Lee et al. The thermodynamic bound on the radiation energy is also estimated separately. The energy-conversion efficiency of the radiation process is discussed. The results are consistent with observations.

Wu, C. S.↗
NASA NTRS1989

Cyclotron resonant scattering in the spectra of gamma-ray bursts

Fits of theoretical spectra from Monte Carlo radiation-transfer calculations to dips at approximately 20 and 40 keV in a spectrum of the gamma-ray burst source GB 880 205 give best-fit values and 68 percent-confidence intervals for the magnetic field of (1.71 + or - 0.07) x 10 to the 12th G, the electron density of (1.2 + or - 0.6) x 10 to the 21st electrons/cm-squared, and the cosine of the viewing angle relative to the field of 0.31 + or - 0.05. The dips observed at approximately 20 keV in the spectra are interpreted as cyclotron resonant scattering, in which electrons undergo radiative 0 to 1 to 0 Landau transitions initiated by photons near the first harmonic. Physical self-consistency fixes the temperature, and the equilibrium temperature equals 5.3 + 0.3 or - 0.2 keV. These results suggest that this gamma-ray burst and many others which exhibit a low-energy dip originate from strongly magnetic neutron stars and are galactic in origin.

Wang, J. C. L.↗
NASA NTRS1995

Space and radiation protection: scientific requirements for space research

Ionizing radiation poses a significant risk to humans living and working in space. The major sources of radiation are solar disturbances and galactic cosmic rays. The components of this radiation are energetic charged particles, protons, as well as fully ionized nuclei of all elements. The biological effects of these particles cannot be extrapolated in a straightforward manner from available data on x-rays and gamma-rays. A radiation protection program that meets the needs of spacefaring nations must have a solid scientific basis, capable not only of predicting biological effects, but also of making reliable estimates of the uncertainty in these predictions. A strategy leading to such predictions is proposed, and scientific requirements arising from this strategy are discussed.

NASA Discipline Radiation Health↗
NASA NTRS1984

Relativistic dispersion and the generation of auroral kilometric radiation

Under the conditions at which auroral kilometric radiation (AKR) is known to be produced by a plasma sheet electron region, relativistic effects of the dispersion of extraordinary-mode waves near the electron cyclotron frequency are found to be very significant. The application of linear theory and computer simulation to a model distribution indicates that an extraordinary mode of a particular Reynolds number dominated the radiation emission due to the cyclotron maser instability, suggesting that hot electrons determine the propagation characteristics of AKR and that larger growth rates are possible for direct amplification of extraordinary waves in the auroral region than had been predicted by calculations employing cold plasma dispersion.

Pritchett, P. L.↗
NASA NTRS2016

Team Update on North American Proton Facilities for Radiation Testing

In the wake of the closure of the Indiana University Cyclotron Facility (IUCF), this presentation provides an overview of the options for North American proton facilities. This includes those in use by the aerospace community as well as new additions from the cancer therapy regime. In addition, proton single event testing background is provided for understanding the criteria needed for these facilities for electronics testing.

Single event effects testing↗
NASA NTRS2016

Team Update on North American Proton Facilities for Radiation Testing

In the wake of the closure of the Indiana University Cyclotron Facility (IUCF), this presentation provides an overview of the options for North American proton facilities. This includes those in use by the aerospace community as well as new additions from the cancer therapy regime. In addition, proton single event testing background is provided for understanding the criteria needed for these facilities for electronics testing.

Proton cyclotrons↗
NASA NTRS2016

Team Update on North American Proton Facilities for Radiation Testing

In the wake of the closure of the Indiana University Cyclotron Facility (IUCF), this presentation provides an overview of the options for North American proton facilities. This includes those in use by the aerospace community as well as new additions from the cancer therapy regime. In addition, proton single event testing background is provided for understanding the criteria needed for these facilities for electronics testing.

Single event effects testing↗
NASA NTRS2016

Team Update on North American Proton Facilities for Radiation Testing

In the wake of the closure of the Indiana University Cyclotron Facility (IUCF), this presentation provides an overview of the options for North American proton facilities. This includes those in use by the aerospace community as well as new additions from the cancer therapy regime. In addition, proton single event testing background is provided for understanding the criteria needed for these facilities for electronics testing.

Cancer therapy↗
NASA NTRS2007

Global Simulation of Electromagnetic Ion Cyclotron Waves

It is very well known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and particles. Such a self-consistent model is being progressively developed by Khazanov et al. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. We will discuss the recent progress in understanding EMIC waves formation mechanisms in the inner magnetosphere. This problem remains unsettled in spite of many years of experimental and theoretical studies. Modern satellite observations by CRRES, Polar and Cluster still do not reveal the whole picture experimentally since they do not stay long enough in the generation region to give a full account of all the spatio-temporal structure of EMIC waves. The complete self-consistent theory taking into account all factors significant for EMIC waves generation remains to be developed. Several mechanisms are discussed with respect to formation of EMIC waves, among them are nonlinear modification of the ionospheric reflection by precipitating energetic protons, modulation of ion-cyclotron instability by long-period (Pc3/4) pulsations, reflection of waves from layers of heavy-ion gyroresonances, and nonlinearities of wave generation process. We show that each of these mechanisms have their attractive features and explains certain part experimental data but any of them, if taken alone, meets some difficulties when compared to observations. We conclude that development of a refined nonlinear theory and further correlated analysis of modern satellite and ground-based data is needed to solve this very intriguing problem.

Khazanov, George V.↗
NASA NTRS2007

Global Simulation of Electromagnetic Ion Cyclotron Waves

It is well known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002 - 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. We will discuss the recent progress in understanding EMIC waves formation mechanisms in the inner magnetosphere. This problem remains unsettled in spite of many years of experimental and theoretical studies. Modern satellite observations by CRRES, Polar and Cluster still do not reveal the whole picture experimentally since they do not stay long enough in the generation region to give a full account of all the spatio-temporal structure of EMIC waves. The complete self-consistent theory taking into account all factors significant for EMIC waves generation remains to be developed. Several mechanisms are discussed with respect to formation of EMIC waves, among them are nonlinear modification of the ionospheric reflection by precipitating energetic protons, modulation of ion-cyclotron instability by long-period (Pc3/4) pulsations, reflection of waves from layers of heavy-ion gyroresonances, and nonlinearities of wave generation process. We show that each of these mechanisms have their attractive features and explains certain part experimental data but any of them, if taken alone, meets some difficulties when compared to observations. We conclude that development of a refined nonlinear theory and further correlated analysis of modern satellite and ground-based data is needed to solve this very intriguing problem.

Khazanov, G. V.↗
NASA NTRS1979

A theory of the terrestrial kilometric radiation

During magnetospheric substorms, electrons with energies of about 1 keV are injected from the plasma-sheet region into the auroral region. A fraction of these energetic electrons can precipitate into the upper atmosphere, and the rest are reflected because of the mirror effect of the convergent geomagnetic field. It is found that these reflected electrons can result in the amplification of electromagnetic waves via a relativistic normal cyclotron resonance. This process may explain the recently discovered terrestrial kilometric radiation.

Wu, C. S.↗
NASA NTRS2008

High-Altitude Emission from Pulsar Slot Gaps: The Crab Pulsar

We present results of a 3D model of optical to gamma-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high-altitudes in the unscreened electric field of the slot gap reach radiation-reaction limited Lorentz factors of approx. 2 x 10(exp 7), while electron-positron pairs from lower-altitude cascades flow along field lines interior to the slot gap. The curvature, synchrotron and inverse Compton radiation of both primary electrons and pairs produce a broad spectrum of emission from infra-red to GeV energies. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles. Synchrotron radiation from pairs with a power-law energy spectrum from gamma = 10(exp 2) - 10(exp 5), dominate the spectrum up to approx. 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. We examine the energy-dependent pulse profiles and phase-resolved spectra for parameters of the Crab pulsar as a function of magnetic inclination alpha and viewing angle zeta, comparing to broad-band data. In most cases, the pulse profiles are dominated by caustics on trailing field lines. We also explore the relation of the high-energy and the radio profiles, as well as the possibility of caustic formation in the radio cone emission. We find that the Crab pulsar profiles and spectrum can be reasonably well reproduced by a model with alpha = 45deg and zeta approx. 100deg or 80deg. This model predicts that the slot gap emission below 200 MeV will exhibit correlations in time and phase with the radio emission.

Harding, Alice K.↗
NASA NTRS2007

Reply to "Comment on 'A Self-Consistent Model of the Interacting Ring Current Ions and Electromagnetic Ion Cyclotron Waves, Initial Results: Waves and Precipitation Fluxes' and 'Self-Consistent Model of the Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves: Waves in Multi-Ion Magnetosphere' by Khazanov et al. et al."

It is well-known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wavenormal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and[ particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002, 2006, 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. Thome and Home [2007] (hereafter referred to as TH2007) call the Khazanov et al. [2002, 2006] results into question in their Comment. The points in contention can be summarized as follows. TH2007 claim that: (1) "the important damping of waves by thermal heavy ions is completely ignored", and Landau damping during resonant interaction with thermal electrons is not included in our model; (2) EMIC wave damping due to RC O + is not included in our simulation; (3) non-linear processes limiting EMIC wave amplitude are not included in our model; (4) growth of the background fluctuations to a physically significantamplitude"must occur during a single transit of the unstable region" with subsequent damping below bi-ion latitudes,and consequently"the bounce averaged wave kinetic equation employed in the code contains a physically erroneous 'assumption". Our reply will address each of these points as well as other criticisms mentioned in the Comment. TH2007 are focused on two of our papers that are separated by four years. Significant progress in the self-consistent treatment of the RC-EMIC wave system has been achieved during those years. The paper by Khazanov et al. [2006] presents the latest version of our model, and in this Reply we refer mostly to this paper.

Khazanov, G. V.↗
NASA NTRS2022

EMIC-Wave Driven Electron Precipitation Observed by CALET on the International Space Station

We present an analysis of the relativistic electron precipitation (REP) event measured by the CALorimetric Electron Telescope (CALET) experiment on board the International Space Station during a relatively weak geomagnetic storm on 31 December 2016. CALET observations were compared with the measurements of the Van Allen Probes in the near-equatorial plane to investigate the global radiation belt dynamics and the REP drivers. The magnetically conjugate observations from these two missions demonstrate that the significant MeV precipitation directly detected by CALET in low-Earth orbit during a period of radiation belt depletion following the passage of a high-speed stream, was associated with dusk-side electromagnetic ion cyclotron (EMIC) waves. In addition, the combined wave, REP and trapped electron data suggest that the reported radiation belt depletion can be likely ascribed to the concomitant loss effects of EMIC wave scattering driving the atmospheric precipitation, as well as outward radial diffusion associated with magnetopause shadowing.

Radiation belts↗
NASA NTRS1990

Source region of the smooth high-frequency nightside Uranus kilometric radiation - A ray-tracing study

This paper presents a plasma density model for the Uranus nightside at r less than 4.2 r(u), developed on the basis of radio wave observations of the Planetary Radio Astronomy instrument on board the Voyager 2 spacecraft and on cyclotron maser instability. The results provide an accurate description of the Uranus kilometric radiation (UKR) source region dependent on a minimum of assumptions, and indicate that the UKR source region is more extended in longitude than previosly determined.

Menietti, J. D.↗
NASA NTRS1987

The main source of radio emission from the magnetosphere of Uranus

Observations of kilometric radiation from Uranus made with the planetary radio astronomy experiment on the Voyager 2 spacecraft are presented and discussed. Similarities between the auroral kilometric radiation from earth and the observed Uranus emission are pointed out. A geometrical beaming model is developed in which a single distributed source is located above the darkside auroral region and emits in the extraordinary mode by the cyclotron maser process. The model can account for nearly all the Uranian kilometric radiation from the high-frequency limit near 850 kHz down to about 150 kHz and for much of it down to the lower limit of 20 kHz.

Gulkis, Samuel↗