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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Electron Trapping and Charge Transport by Large Amplitude Whistlers

Trapping of electrons by magnetospheric whistlers is investigated using data from the Waves experiment on Wind and the S/WAVES experiment on STEREO. Waveforms often show a characteristic distortion which is shown to be due to electrons trapped in the potential of the electrostatic part of oblique whistlers. The density of trapped electrons is significant, comparable to that of the unperturbed whistler. Transport of these trapped electrons to new regions can generate potentials of several kilovolts, Trapping and the associated potentials may play an important role in the acceleration of Earth's radiation belt electrons.

Kellogg, P. J.↗
DOE OSTI2023

Lowest-order QED radiative corrections in unpolarized elastic electron–deuteron scattering beyond the ultra-relativistic limit for the proposed deuteron charge radius measurement at Jefferson laboratory

Analogous to the well-known proton charge radius puzzle, a similar puzzle exists for the deuteron charge radius, r d . There are discrepancies observed in the results of r d , measured from electron-deuteron (e - d) scattering experiments, as well as from atomic spectroscopy. In order to help resolve the charge radius puzzle of the deuteron, the PRad collaboration at Jefferson Lab has proposed an experiment for measuring r d , named DRad. This experiment is designed to measure the unpolarized elastic e - d scattering cross section in a low-Q 2 region. To extract the cross section with a high precision, having reliable knowledge of QED radiative corrections is important. Here, in this paper, we present complete numerical calculations of the lowest-order radiative corrections in e - d scattering for the DRad kinematics. The calculations have been performed within a covariant formalism and beyond the ultra-relativistic approximation ($m^2_e$ $\ll$ Q 2 ). Besides, we present a systematic uncertainty on r d arising from higher-order radiative corrections, estimated based on our cross-section results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Validation of the SCEPTRE Boltzmann-CSD Solver

A new Boltzmann-CSD solver has been developed within the SCEPTRE radiation-transport code, based on the 1st-order form of the transport equation, using discontinuous finite elements in space and energy and discrete ordinates in angle. The Boltzmann-CSD solver has been validated against experimental data for electron energy deposition distributions and for electron emission spectra. Comparison of the calculated results with experimental data shows excellent agreement for many of the test configurations and reasonable agreement for other test configurations. The tests have also been modeled with the ITS Monte Carlo code, which also shows excellent to reasonable agreement with the SCEPTRE results and experimental data. The SCEPTRE Boltzmann-CSD solver relies on electron cross sections generated by the legacy CEPXS code, which currently is limited to electron-only Boltzmann-CSD cross sections. Performing full electron-photon radiation transport with the Boltzmann-CSD solver will require further development in the cross section generating code. For the energy- deposition calculations, neglecting photon transport results in at most about 5% overprediction of the energy deposition for high-energy electrons on high-Z targets, and relatively insignificant difference for the other test configurations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1976

Radiation of whistlers by helical electron and proton beams

The feasibility of generating whistlers by means of an array of helical electron and proton beams is investigated. It is found that quasi-static beam-plasma instabilities will play a vital role in limiting the effective coherent length of the beam. The total radiated power for the whistlers is consequently decreased by 2 orders of magnitude below previously predicted levels (Dowden, 1973). A proton beam is shown to be somewhat less efficient than an electron beam for generating whistlers.

Kuo, Y.-Y.↗
DOE OSTI2024

Power density calculation of spontaneous radiation emission from a finite emittance electron beam in planar undulators

We extend the angular power density formulae for spontaneous radiation emission from planar undulators to include finite emittance and angular misalignment of the electron beam. Then we calculate and compare power densities estimated from integral approach with Gaussian beam distribution and summation approach with macro-particle allocation covering particle beam phase space. After showing that both approaches converge to each other, we apply the macro-particle approach to study power absorbed and transmitted by various apertures at front end of 9-ID beamline at National Synchrotron Light Source-II for misaligned electron beam. Our analysis indicate that the electron beam misalignment could lead to unwarranted power deposition at tighter apertures that would have been otherwise difficult to account for during the aperture design/choice process.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Observation of a THz-sub-THz spontaneous coherent undulator radiation driven by a low energy electron beam from a thermionic RF electron gun

In this work, we report observations of an intense, multi-band, sub-THz and THz radiation extracted from a similar to 2-3 MeV electron beam with a flat transverse profile propagating in an oversized rectangular waveguide placed into a 3.25 mm gap of a planar undulator having 1.3 cm period and similar to 20 cm length. Radiation outcoupling is accomplished using a horn antenna and a miniature permanent in-vacuum magnet separating the mm-sub-mm-waves and electron beam. A table-top experiment utilizes a radio frequency thermionic electron gun delivering a thousand momentum-chirped microbunches per macropulse and an alpha-magnet producing microbunches of a sub-mm length. Total radiated energy of a sub-millijoule per a microsecond radio frequency macropulse is demonstrated with flux more than ten micro-Joules per centimeter squared. With 1 THz filter the energy measured is about 1 microjoule and flux of a few micro-Joules per centimeter squared.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1985

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

In an effort to elucidate the changes in molecular structural and mechanical properties of epoxy/graphite fiber composites upon exposure to ionizing radiation in a simulated space environment, spectroscopic and surface properties of tetraglycidyl-4,4'-diamino diphenyl methane (TGDDM) red with diamino diphenyl sulfone (DDS) and T-300 graphite fiber were investigated following exposure to ionizing radiation. Cobalt-60 gamma radiation and 1/2 MeV electrons were used as radiation sources. The system was studied using electron spin resonance (ESR) spectroscopy, infrared absorption spectroscopy, contact angle measurements, and electron spectroscopy for chemical analysis.

Fornes, R. E.↗
NASA NTRS2010

Method and Circuit for In-Situ Health Monitoring of Solar Cells in Space

This innovation represents a method and circuit realization of a system designed to make in-situ measurements of test solar-cell operational parameters on orbit using readily available high-temperature and high-ionizing-radiation- tolerant electronic components. This innovation enables on-orbit in-situ solar-array health monitoring and is in response to a need recognized by the U.S. Air Force for future solar arrays for unmanned spacecraft. This system can also be constructed out of commercial-grade electronics and can be embedded into terrestrial solar power system as a diagnostics instrument. This innovation represents a novel approach to I-V curve measurement that is radiation and temperature hard, consumes very few system resources, is economical, and utilizes commercially available components. The circuit will also operate at temperatures as low as 55 C and up to +225 C, allowing it to reside close to the array in direct sunlight. It uses a swept mode transistor functioning as a resistive load while utilizing the solar cells themselves as the biasing device, so the size of the instrument is small and there is no danger of over-driving the cells. Further, this innovation utilizes nearly universal spacecraft bus resources and therefore can be readily adapted to any spacecraft bus allowing for ease of retrofit, or designed into new systems without requiring the addition of infrastructure. One unique characteristic of this innovation is that it effects the measurement of I-V curves without the use of large resistor arrays or active current sources normally used to characterize cells. A single transistor is used as a variable resistive load across the cell. This multi-measurement instrument was constructed using operational amplifiers, analog switches, voltage regulators, MOSFETs, resistors, and capacitors. The operational amplifiers, analog switches, and voltage regulators are silicon-on-insulator (SOI) technology known for its hardness to the effects of ionizing radiation. The SOI components used can tolerate temperatures up to 225 C, which gives plenty of thermal headroom allowing this circuit to perhaps reside in the solar cell panel itself where temperatures can reach over 100 C.

Krasowski, Michael J.↗
NASA NTRS2024

Revisiting High-Energy Polarization from Leptonic and Hadronic Blazar Scenarios

X-ray and MeV polarization can be powerful diagnostics for leptonic and hadronic blazar models. Previous predictions are mostly based on a one-zone framework. However, recent IXPE observations of Mrk 421 and 501 strongly favor a multizone framework. Thus, the leptonic and hadronic polarization predictions need to be revisited. Here we identify two generic radiation transfer effects, namely, double depolarization and energy stratification, that can have an impact on the leptonic and hadronic polarization. We show how they are generalized from previously known multizone effects of the primary electron synchrotron radiation. Under our generic multizone model, the leptonic polarization degree is expected to be much lower than the one-zone prediction, unlikely detectable in most cases. The hadronic polarization degree can reach a value as high as the primary electron synchrotron polarization during simultaneous multiwavelength flares, consistent with the one-zone prediction. Therefore, IXPE and future X-ray and MeV polarimeters such as eXTP, COSI, and AMEGO-X, have good chances to detect hadronic polarization during flares. However, the hadronic polarization cannot be well constrained during the quiescent state. Nonetheless, if some blazar jets possess relatively stable large-scale magnetic structures, as suggested by radio observations, a nontrivial polarization degree may show up for the hadronic model after a very long exposure time (≳1 yr).

Haocheng Zhang↗
DOE OSTI2020

Radiative capture rates at deep defects from electronic structure calculations

We present a methodology to calculate radiative carrier capture coefficients at deep defects in semiconductors and insulators from first principles. Electronic structure and lattice relaxations are accurately described with hybrid density functional theory. Calculations of capture coefficients provide an additional validation of the accuracy of these functionals in dealing with localized defect states. We also discuss the validity of the Condon approximation, showing that even in the event of large lattice relaxations the approximation is accurate. We test the method on GaAs:VGa-TeAs and GaN:CN, for which reliable experiments are available, and demonstrate very good agreement with measured capture coefficients.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Mass ejection from the O4f star Zeta Puppis

Profiles of P Cygni lines and displaced absorption lines observed in high-resolution Copernicus UV scans of Zeta Pup from 907 to 1738 A are compared with profile calculations to derive an optical-depth scale of the lines as a function of height or velocity in the expanding envelope. The degrees of ionization of the elements C, N, O, Si, and S under equilibrium conditions at electron temperatures of 20,000 to 1 million K, radiation temperatures of 20,000 to 50,000 K, and electron number densities of 100 million to 1 trillion per cu cm are computed with a dilution factor of 0.1, taking into account collisional ionization by electrons, radiative ionization from the ground state, radiative recombination, and dielectric recombination. Observed and predicted relative ionization fractions are then compared to determine the electron and radiation temperatures. Crude and refined estimates of the mass-loss rate and velocity law are made, and radiative acceleration in the expanding envelope is analyzed. The derived model for Zeta Pup is found to have a mass-loss rate of about 7.2 millionths of a solar mass per year, a wind velocity that increases slowly outward and reaches 700 km/s about 28 solar masses, and a nearly isothermal envelope with an electron temperature of approximately 200,000 K.

Lamers, H. J. G. L. M.↗
DOE OSTI2023

Two-dimensional spin systems in PECVD-grown diamond with tunable density and long coherence for enhanced quantum sensing and simulation

Systems of spins engineered with tunable density and reduced dimensionality enable a number of advancements in quantum sensing and simulation. Defects in diamond, such as nitrogen-vacancy (NV) centers and substitutional nitrogen (P1 centers), are particularly promising solid-state platforms to explore. However, the ability to controllably create coherent, two-dimensional spin systems and characterize their properties, such as density, depth confinement, and coherence, is an outstanding materials challenge. We present a refined approach to engineer dense (≳1 ppm ∙ nm), 2D nitrogen, and NV layers in diamond using delta-doping during plasma-enhanced chemical vapor deposition epitaxial growth. We employ both traditional materials techniques, e.g., secondary ion mass spectrometry, alongside NV spin decoherence-based measurements to characterize the density and dimensionality of the P1 and NV layers. We find P1 densities of 5–10 ppm ∙ nm, NV densities between 1 and 3.5 ppm ∙ nm tuned via electron irradiation dosage, and depth confinement of the spin layer down to 1.6 nm. We also observe high (up to 0.74) ratios of NV to P1 centers and reproducibly long NV coherence times, dominated by dipolar interactions with the engineered P1 and NV spin baths.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effects of screening and pressure ionization on the electron broadening of spectral lines in dense plasmas

Collisions between electrons and radiating atoms broaden spectral absorption and emission lines in dense plasmas. High densities also introduce screening and pressure ionization effects that distort the wave functions of both bound and free electrons. In order to study how dense plasma effects influence the electron broadening of spectral lines, this paper incorporates electron wave functions from an average-atom (AA) model to calculate the linewidth of the B III 2⁢𝑝−2⁢𝑠 transition at 𝑇 = 10 eV for mass densities ranging from 𝜌 = 10 −4 to 0.4⁢ g⁡/cc. The calculation method uses the impact approximation, allowing the linewidth to be written in terms of electron-collision cross sections and an interference term. Compared to an otherwise identical calculation that uses Coulomb free wave functions, the AA method is found to modify both the cross sections and the resulting linewidth at sufficiently high density by introducing screening and pressure-ionized bound states. Screening lowers the cross sections at low energies and near electron excitation thresholds, while pressure-ionized bound states introduce resonances into the continuum. Thus, as the density increases, the relative linewidth between the AA and Coulomb calculations follows a general decrease because of screening, with sharp increases at various intervals due to pressure ionization. Finally, the AA results are also compared with a common approach to introduce screening through the interaction potential and reduced models that use the Bethe formula for the inelastic electron-collision cross sections.

electronic excitation & ionization↗
NASA NTRS1980

Radiation tolerance of boron doped dendritic web silicon solar cells

The potential of dendritic web silicon for giving radiation hard solar cells is compared with the float zone silicon material. Solar cells with n(+)-p-P(+) structure and approximately 15% (AMl) efficiency were subjected to 1 MeV electron irradiation. Radiation tolerance of web cell efficiency was found to be at least as good as that of the float zone silicon cell. A study of the annealing behavior of radiation-induced defects via deep level transient spectroscopy revealed that E sub v + 0.31 eV defect, attributed to boron-oxygen-vacancy complex, is responsible for the reverse annealing of the irradiated cells in the temperature range of 150 to 350 C.

Rohatgi, A.↗
NASA NTRS2008

LETS: Lunar Environments Test System

The Environmental Effects Branch (EM50) at the Marshall Space Flight Center has developed a unique capability within the agency, namely the Lunar Environment Test System (LETS). LETS is a cryo-pumped vacuum chamber facility capable of high vacuum (10-7 Torr). LETS is a cylindrical chamber, 30 in. (0.8 m) diameter by 48 in. (1.2 m) long thermally controlled vacuum system. The chamber is equipped with a full array of radiation sources including vacuum ultraviolet, electron, and proton radiation. The unique feature of LETS is that it contains a large lunar simulant bed (18 in. x 40 in. x 6 in.) holding 75 kg of JSC-1a simulant while operating at a vacuum of 10-7 Torr. This facility allows three applications: 1) to study the charging, levitation and migration of dust particles, 2) to simulate the radiation environment on the lunar surface, and 3) to electrically charge the lunar simulant enhancing the attraction and adhesion of dust particles to test articles more closely simulating the lunar surface dust environment. LETS has numerous diagnostic instruments including TREK electrostatic probes, residual gas analyzer (RGA), temperature controlled quartz crystal microbalance (TQCM), and particle imaging velocimeter (PIV). Finally, LETS uses continuous Labview data acquisition for computer monitoring and system control.

Vaughn, Jason A.↗
NASA NTRS2011

Deducing Electron Properties from Hard X-Ray Observations

X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions regarding the energy, angular (pitch angle) and spatial distributions of energetic electrons in solar flares are critically reviewed. We discuss the role and the observational evidence of several radiation processes: free-free electron-ion, free-free electron-electron, free-bound electron-ion, photoelectric absorption and Compton backscatter (albedo), using both spectroscopic and imaging techniques. This unprecedented quality of data allows for the first time inference of the angular distributions of the X-ray-emitting electrons and improved model-independent inference of electron energy spectra and emission measures of thermal plasma. Moreover, imaging spectroscopy has revealed hitherto unknown details of solar flare morphology and detailed spectroscopy of coronal, footpoint and extended sources in flaring regions. Additional attempts to measure hard X-ray polarization were not sufficient to put constraints on the degree of anisotropy of electrons, but point to the importance of obtaining good quality polarization data in the future.

Kontar, E. P.↗
NASA NTRS1978

Spontaneous emission near the electron plasma frequency in a plasma with a runaway electron tail

Spontaneous emission of radiation with frequencies near the electron plasma frequency is studied for a plasma which consists of both thermal and runaway electrons. It is found that a substantial enhancement of the spontaneous radiation intensity can occur in this frequency regime via a Cherenkov resonance with the runaway electrons. Numerical analysis indicates that, for reasonable estimates of densities and energies, the plasma-frequency radiation can attain levels greater than the peak thermal emission at the second gyroharmonic.

Freund, H. P.↗
NASA NTRS2004

Self-Recovery Experiments in Extreme Environments Using a Field Programmable Transistor Array

Temperature and radiation tolerant electronics, as well as long life survivability are key capabilities required for future NASA missions. Current approaches to electronics for extreme environments focus on component level robustness and hardening. However, current technology can only ensure very limited lifetime in extreme environments. This paper describes novel experiments that allow adaptive in-situ circuit redesign/reconfiguration during operation in extreme temperature and radiation environments. This technology would complement material/device advancements and increase the mission capability to survive harsh environments. The approach is demonstrated on a mixed-signal programmable chip (FPTA-2), which recovers functionality for temperatures until 28 C and with total radiation dose up to 250kRad.

space vehicle electronics↗