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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

An Improved Magnetic Field Model for Jupiter's Inner Magnetosphere Using a Microsignature of Amalthea

Observation of a particle absorption microsignature of the Jovian satellite Amalthea during the Pioneer II close flyby of Jupiter on December 3, 1974, has been described by McKibben et al. The microsignature was also observed by the University of Iowa/Pioneer II instrument in the distribution of protons in the kinetic energy range 0.61 less than T(sub p) less than 3.41 MeV but has not been previously reported. The finer time resolution and superior data quality of the latter observations provide a fresh basis for assessing the accuracy with which various published magnetic field models of Jupiter's magnetic field models describe Jupiter's magnetic field for radial distances of the order of or less than several planetary radii. The expected time of occurrence of the minimum of Amalthea's microsignature was calculated for each model and compared to the time of the observed minimum. The discrepancy between these two times was significant for each of the published models, but it could be reduced to zero by interpolating between two of the closely related models. The spherical harmonic coefficients of this combination model are tabulated. Also included is a novel method for calculating the intensity-time profile of the microsignature. In a later paper, the improved model is utilized to analyze the energetic particle measurements in Jupiter's innermost magnetosphere by the Galileo entry probe in December 1995.

Randall, Bruce A.↗
NASA NTRS2007

Photodiode Preamplifier for Laser Ranging With Weak Signals

An improved preamplifier circuit has been designed for processing the output of an avalanche photodiode (APD) that is used in a high-resolution laser ranging system to detect laser pulses returning from a target. The improved circuit stands in contrast to prior such circuits in which the APD output current pulses are made to pass, variously, through wide-band or narrow-band load networks before preamplification. A major disadvantage of the prior wide-band load networks is that they are highly susceptible to noise, which degrades timing resolution. A major disadvantage of the prior narrow-band load networks is that they make it difficult to sample the amplitudes of the narrow laser pulses ordinarily used in ranging. In the improved circuit, a load resistor is connected to the APD output and its value is chosen so that the time constant defined by this resistance and the APD capacitance is large, relative to the duration of a laser pulse. The APD capacitance becomes initially charged by the pulse of current generated by a return laser pulse, so that the rise time of the load-network output is comparable to the duration of the return pulse. Thus, the load-network output is characterized by a fast-rising leading edge, which is necessary for accurate pulse timing. On the other hand, the resistance-capacitance combination constitutes a lowpass filter, which helps to suppress noise. The long time constant causes the load network output pulse to have a long shallow-sloping trailing edge, which makes it easy to sample the amplitude of the return pulse. The output of the load network is fed to a low-noise, wide-band amplifier. The amplifier must be a wide-band one in order to preserve the sharp pulse rise for timing. The suppression of noise and the use of a low-noise amplifier enable the ranging system to detect relatively weak return pulses.

Abramovici, Alexander↗
NASA NTRS1979

Observation of an impulsive solar X-ray burst from a coronal source

Observations of the spatial, spectral, and temporal structure of an impulsive hard X-ray source in a behind-the-limb solar flare have been made with high-time-resolution hard X-ray detectors aboard two spacecraft, the International Sun Earth Explorer 3 (ISEE 3) and the Pioneer Venus Orbiter (PVO), which were separated in heliographic longitude by about 12.5 deg. The principal findings are that (1) the coronal part of the X-ray source is about 600 times less intense than the lower-altitude part of the source; and (2) the coronal X-ray observations are consistent with a power-law electron spectrum which extends down to about 5 keV.

Kane, S. R.↗
NASA NTRS1977

Impulsive solar X-ray bursts

A set of 22 simple, impulsive solar flares, identified in the OSO-5 hard X-ray data, were analyzed together with coincident microwave and meterwave radio observations. The rise times and fall times of the X-ray bursts are found to be highly correlated and effectively equal, strongly suggesting a flare energizing mechanism that is reversible. The good time resolution available for these observations reveals that the microwave emission is influenced by an additional process, evident in the tendency of the microwave emission to peak later and decay more slowly than the symmetric X-ray bursts. Meterwave emission is observed in coincidence with the 5 events which show the strongest time correlation between the X-ray and microwave burst structure. This meterwave emission is characterized by U-burst radiation, indicating confinement of the flare source.

Crannell, C. J.↗
NASA NTRS1981

Detailed study on acceleration and propagation of energetic protons and electrons in the magnetotail during substorm activity

High time resolution measurements of energetic particles and magnetic field measurements by the IMP 8 satellite in the distant magnetotail are presented for November 26, 1973, when exceptionally intense particle bursts were detected by both the IMP 7 and 8 spacecraft. During the onset of the most intense burst as well as at other times, oppositely directed anisotropies of protons and electrons parallel to the tail field and lasting up to about 60 sec were observed, implying the presence of field-aligned electric fields. The particle and field observations are discussed in the context of proposed mechanisms for the acceleration of particles during various dynamical magnetospheric processes. Satellite instrument readings are presented through the extensive use of graphs.

Kirsch, E.↗
NASA NTRS1989

The BATSE experiment on the Gamma Ray Observatory: Solar flare hard x ray and gamma-ray capabilities

The Burst and Transient Source Experiment (BATSE) for the Gamma Ray Observatory (GRO) consists of eight detector modules that provide full-sky coverage for gamma-ray bursts and other transient phenomena such as solar flares. Each detector module has a thin, large-area scintillation detector (2025 sq cm) for high time-resolution studies, and a thicker spectroscopy detector (125 sq cm) to extend the energy range and provide better spectral resolution. The total energy range of the system is 15 keV to 100 MeV. These 16 detectors and the associated onboard data system should provide unprecedented capabilities for observing rapid spectral changes and gamma-ray lines from solar flares. The presence of a solar flare can be detected in real-time by BATSE; a trigger signal is sent to two other experiments on the GRO. The launch of the GRO is scheduled for June 1990, so that BATSE can be an important component of the Max '91 campaign.

Fishman, G. J.↗
NASA NTRS1992

COMPTEL: Instrument description and performance

The imaging Compton telescope (COMPTEL) is one of the four gamma ray detectors aboard the Compton Gamma Ray Observatory (GRO). COMPTEL is sensitive to gamma rays from 800 keV to 30 MeV with a field of view of approximately 1 sr. Its angular resolution ranges between 1 and 2 degrees depending on the energy and incidence angle. The energy resolution of better than 10 percent FWHM enables COMPTEL to provide spectral resolution in the regime of astrophysical nuclear lines. The effective area varies typically from 10 to 50 cm(exp 2) depending on the energy and event selections made. In its telescope mode, COMPTEL is able to study a wide variety of objects, pointlike as well as extended in space. With 0.125 msec timing resolution, pulsed emission can be studied. In the single detector mode, COMPTEL uses two of its detectors to study the temporal spectral evolution of strong gamma ray bursts or transients.

Denherder, J. W.↗
NASA NTRS2010

The Latest Space-Borne Observations of TGFs from Fermi-GBM

The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope Observatory (Fermi) is detecting about two TGFs per week. This rate has increased by a factor of approx.eight since launch when flight software was uploaded to the spacecraft in November 2009 in order to increase the sensitivity of GBM to TGFs. Weaker, un-triggered TGFs are now also being observed about once per day over selected low-latitude regions Americas. The high efficiency and time resolution (2 s) of GBM allows temporal features to be resolved so that some insight may be gained on the origin and transport of the gamma-ray photons through the atmosphere. TGFs are observed to be shorter than previously thought, with an average duration of approx.100 micro-s. The absolute times of TGFs are known to approx.10 micro-s, allowing accurate correlations of TGFs with lightning networks and other lightning-related phenomena. The events are observed in the thick bismuth germanate (BGO) scintillation detectors of GBM with photon energies above 40 MeV. Other new results on the temporal and spectral characteristics of TGFs will be presented, along with properties of several electron-positron TGF events that have been identified.

Fishman, Gerald J.↗
DOE OSTI2024

Low Energy Neutron-induced Charged-particle (Z) (LENZ) instrument development with a focus on pulse shape discrimination for low-energy charged particles

To study neutron-induced charged-particle reactions with high precision, the Low Energy Neutron-induced Charged-particle (Z) instrument (LENZ) was developed at the Los Alamos Neutron Science Center. For the interest of measuring (n,p) and (n, α) reactions simultaneously, Pulse Shape Discrimination methods were investigated to identify different charged particles in the energy range of 3 - 20 MeV and improve signal-to-background ratios using Double-sided Silicon Strip Detectors and waveform digitizers. The risetime and pulse shape properties of detected charged particles were characterized for various silicon detector’s thickness with different orientations. During the post-processing of waveforms, we implemented different digital filters for effective particle identifications and improved energy- and timing- resolutions. We validated the optimized digital filters and pulse shape analyses, via measurements with 228 Th and 229 Th calibration sources, proton-induced reactions on a 7 LiF target, and neutron-induced reactions on CH 2 , Ta 2 O 5 , 58 Ni, and 6 LiF/ 59 Ni targets at the time-of-flight facility, LANSCE. In conclusion, the summary of effective thresholds and Figure of Merits on separating different charged particles is reported.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1978

Impulsive solar X-ray bursts

A set of 22 simple impulsive solar flares, identified in the OSO 5 hard X-ray data, has been analyzed together with coincident microwave and meter-wave radio observations. The rise times and fall times of the X-ray bursts are found to be highly correlated and effectively equal, strongly suggesting a flare-energizing mechanism that is reversible. The good time resolution available for these observations reveals that the microwave emission is influenced by an additional process, evident in the tendency of the microwave emission to peak later and decay more slowly than the symmetric X-ray bursts. Meter-wave emission is observed in coincidence with five events which also show strong time correlation between the X-ray and microwave burst structure. This meter-wave emission is characterized by U-burst radiation, indicating confinement of the flare source. The relationship found between the X-ray burst duration and the calculated flare diameter, together with the thermal character of the X-ray spectra, gives additional support to the hypothesis that the impulsive component is driven by adiabatic compression and expansion of a magnetically confined plasma which is the common primary source of both X-ray and microwave emission.

Crannell, C. J.↗
NASA NTRS1993

Magnetosheath-ionospheric plasma interactions in the cusp/cleft. 1: Observations of modulated injections and upwelling ion fluxes

In situ observations of the cusp/cleft are important as they allow a direct investigation of coupling solar wind energy to the ionosphere, plus they provide an opportunity for the remote sensing of the magnetopause. High time resolution observations from Dynamic Explorer 1 are used to investigate these processes. It is shown that in the spacecraft frame the injection is modulated or pulsating with a period of approximately 18-30 s with the injection duration possibly being as short as 6 s. This modulation indicates that there may be fast time scale and/or short scale length processes modulating the injection of the magnetosheath plasma across the magnetopause. In addition, the pulsating injection is seen to modulate the outflow of upwelling ionospheric ions to the magnetosphere. These upwelling ions are seen prior to the magnetosheath ion injection and therefore are not directly created by the injection. During the injection itself, the intensity of the upwelling ions is seen to dramatically decrease but their average energy increases. At end of the magnetosheath injections, the intensity of the upwelling ion flux is seen to increase to levels comparable to levels prior to the magnetosheath injection. On two occasions during the encounter, the particle fluxes are sufficiently high that enhanced downward flows of perpendicularly heated ions, of presumably ionospheric origin, are observed in association with a reduction in the intensity of the upwelling ions. These observations are probably the first detection of downward conics and suggest that there is momentum transfer between the magnetosheath and ionospheric ions. This momentum transfer eventually leads to an enhanced outflow of heated ionospheric plasma where their energy has been raised from a few tens of eV to a few hundred eV.

Winglee, R. M.↗
NASA NTRS1977

Acceleration of protons at 32 Jovian radii in the outer magnetosphere of jupiter

During the inbound pass of Pioneer 10, a rapid ten-fold increase of the 0.2 to MeV proton flux was observed at 32 Jovian radii (R sub J). The total event lasted for 30 minutes and was made up of a number of superimposed individual events. At the time, the spacecraft was in the outer magnetosphere about 7 R sub J below the magnetic equator. Before and after the event, the proton flux was characteristic of the low flux level normally encountered between crossings of the magnetic equator. Flux changes at different energies were coherent within 1 minute; a time comparable to the time resolution of the data. The angular distributions were highly anisotropic with protons streaming towards Jupiter. A field-aligned dumbbell distribution was observed initially, and a pancake distribution just before the flux decayed to its pre-event value. The alpha particle flux changed as rapidly as the proton flux but peaked at different times. The energetic electron flux behaved differently; it increased gradually throughout the period.

Schardt, A. W.↗
NASA NTRS1979

Relationship between hard X-ray and EUV sources in solar flares

The high time resolution hard X-ray (not less than 15 keV) observations of medium and large impulsive solar flares made with the OSO 5 satellite are compared with the simultaneous ground-based observations of 10-1030 A EUV flux made via sudden frequency deviations (SFD) at Boulder. For most flares the agreement between the times of maxima of the impulsive hard X-ray and EUV emissions is found to be consistent with earlier studies (not less than 1 s). The rise and decay times of the EUV emission are larger than the corresponding times for X-rays not less than 30 keV. When OSO 5 hard X-ray measurements are combined with those made by OGO1, OGO 3, OGO 5, and TD 1A satellites, it is found that there is a nearly linear relationship between the energy fluxes of impulsive EUV emission and X-rays not less than 10 keV over a wide range of flare magnitudes. A model involving only a 'partial precipitation' of energetic electrons and consisting of both thick and thin target hard X-ray sources is examined.

Kane, S. R.↗
NASA NTRS1988

Bio-, Magneto- and event-stratigraphy across the K-T boundary

Determining the time and the time structure of rare events in geology can be accomplished by applying three different and independent stratigraphic methods: Biostratigraphy, magneto-stratigraphy and event-stratigraphy. The optimal time resolution of the two former methods is about 1000 years, while by means of event-stratigraphy a resolution of approximately one year can be achieved. For biostratigraphy across the Cretaceous-Tertiary (K-T) boundary micro- and nannofossils have been found best suited. The qualitative and quantitative analyses of minerals and trace elements across the K-T boundary show anomalies on a millimeter scale and permit conclusions regarding the time structure of the K-T event itself. The results of the analyses find a most consistent explanation by the assumption of an extraterrestrial impact. The main portion of the material rain from the atmosphere evidently was deposited within a short time. The long-time components consist of the finest portion of the material rain from the atmosphere and the transported and redeposited fall-out.

Preisinger, A.↗
NASA NTRS2021

Timing Calibration of the NuSTAR X-Ray Telescope

The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first focusing X-ray telescope in the hard X-ray (3–79 keV) band. Among the phenomena that can be studied in this energy band, some require high time resolution and stability: rotation-powered and accreting millisecond pulsars, fast variability from black holes and neutron stars, X-ray bursts, and more. Moreover, a good alignment of the timestamps of X-ray photons to UTC is key for multi-instrument studies of fast astrophysical processes. In this paper, we describe the timing calibration of the NuSTAR mission. In particular, we present a method to correct the temperature-dependent frequency response of the on-board temperature-compensated crystal oscillator. Together with measurements of the spacecraft clock offsets obtained during downlinks passes, this allows a precise characterization of the behavior of the oscillator. The calibrated NuSTAR event timestamps for a typical observation are shown to be accurate to a precision of ∼65 μs.

Matteo Bachetti↗
DOE OSTI2026

Single-shot ultrafast dynamics of nanosecond pulsed plasmas: Transition from ps–ns nonequilibrium to near-full ionization

The ultrafast multi-stage evolution of state-defining properties in atmospheric-pressure nanosecond pulsed plasmas is quantified using single-discharge, jitter-free, continuous streak-sweep spectroscopy of N 2 (C → B) molecular and N + /O + ionic species with a single-shot time resolution as short as ∼160 ps. An early period of extreme nonequilibrium is observed with vibrational temperatures [T V (C)] dropping from ∼8000 K at <200 ps after plasma breakdown to <4000 K within ∼1 ns, with near-ambient rotational temperatures [T R (C)] ∼ 300 K due to limited collisional energy transfer. This early-time T V (C) trend is representative of a direct and unquenched look into the high-energy tail of the electron energy distribution function; thus, it tracks real-time changes in the mean electron energy via the N2(C) emission signatures. This is followed by the rapid onset of N + /O + ionic emission after a distinct time delay of ∼14.9 ns due to multistep chemical kinetics. The ionic emission enables determination of electron densities (n e ) >2 × 10 19 cm −3 and electron temperatures (T e ) >36 000 K, indicating the transition to a nearly fully ionized regime. The ps–ns temporal dynamics are also compared between air and N 2 plasmas to assess the influence of collisional partners, as well as across the anode, cathode, and central gap regions to identify spatial variations in plasma behavior. Finally, this work demonstrates versatile continuously probing approach capable of spectro-temporal and spatially resolved single-shot measurements of key state variables in the ps–ns evolution of atmospheric-pressure nanosecond pulsed plasmas.

Electric discharges↗
DOE OSTI2026

Ultrafast Raman probe of the photoinduced superconducting to normal state transition in the cuprate Bi 2 ⁢Sr 2 ⁢CaCu 2 ⁢O 8+𝛿

Here, we report an ultrafast Time-Resolved Raman scattering study of the out-of-equilibrium photoinduced dynamics across the superconducting to normal state phase transition of the cuprate Bi 2 ⁢Sr 2⁢ CaCu 2 ⁢O 8+𝛿 . Using the polarization-resolved momentum space selectivity of Raman scattering, we track the superconducting condensate destruction and recovery dynamics with subpicoseconds time resolution in the antinodal region of the Fermi surface where the superconducting gap is maximum. Leveraging ultrafast Raman thermometry, we find a significant dichotomy between the superconducting condensate and the quasiparticle temperature dynamics near the antinodes, which cannot be framed in terms of a single effective electron temperature. The present work demonstrates the ability of Time-Resolved Raman scattering to selectively probe out-of-equilibrium pathways of different electronic subdegrees of freedom during a photoinduced phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

CUPRI observations of PMSE during Salvo B of NLC-91: Evidence of both partial relfection and turbulent scatter

During the first rocket sequence (called Salvo B) of the NLC-91 campaign, the Cornell University Portable Radar Interferometer (CUPRI) observed two simultaneously occurring layers of Polar Mesophere Summer Echoes (PMSE). during the time of the Turbo B flight, the high time-resolution CUPRI Doppler spectra exhibited sawtooth-like discontinuities in the lower layer which we interpret to be a distorted partial reflection layer which was advected across the radar beam. The upper layer, on the other hand, appeared to be caused by turbulent scatter and we estimate the turbulence energy dissipation rate in the upper layer at the time of the Turbo B flight to have been approximately 0.04 W/kg. Futhermore, a shift in the antenna beam direction from vertical to 8 deg off zenith revealed an aspect sensitivity of approximately 5 dB in the lower layer but none in the upper layer. We conclude that, at this particular time, turbulent scatter was responsible for the upper layer while some form of partial reflection was dominant in the lower layer.

Cho, John Y. N.↗