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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Propagation and absorption of electron-cyclotron maser radiation during solar flares

The propagation and absorption of the maser radiation during solar flares are examined through linear theory and electromagnetic particle simulations. It is shown using linear theory that strong absorption of the radiation should occur as it propagates toward the second harmonic layer, where the magnetic field is half as strong as in the emission region. Only radiation propagating nearly parallel to the magnetic field in a low-temperature plasma may be able to escape under certain limited conditions. Finite temperature effects can cause radiation propagating nearly perpendicular to the magnetic field to refract, causing enhanced absorption. Particle simulations are then used to evaluate the nonlinear response of the plasma as the maser radiation propagates through the absorption layer. It is shown that some of the maser radiation is able to escape through a process of absorption below the second harmonic of the local gyrofrequency and re-emission above it. The fraction able to escape is much higher than that predicted by linear theory, although the amount of escaping energy is only a small fraction of the incident energy.

Mckean, M. E.↗
DOE OSTI2022

Electromagnetic probes: Theory and experiment

We review the current state of research on electromagnetic probes in the context of heavy-ion collisions. The focus is on thermal photons and dileptons which provide unique insights into the properties of the created hot and dense matter. This review is intended to provide an introductory overview of the topic as well as a discussion of recent theoretical and experimental results. In particular, we discuss the role of vector-meson spectral functions in the calculation of photon and dilepton rates and present recent results obtained from different frameworks. Furthermore, we will highlight the special role of photons and dileptons to provide information on observables such as the temperature, the lifetime, the polarization and the electrical conductivity of the produced medium as well as their use to learn about chiral symmetry restoration and phase transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Mutual synchronization of two stacks of intrinsic Josephson junctions in cuprate superconductors

Certain high-T{sub c} cuprate superconductors, which naturally realize a stack of Josephson junctions, thus can be used to generate electromagnetic waves in the terahertz region. A plate-like single crystal with 10{sup 4} junctions without cavity resonance was proposed to achieve strong radiation. For this purpose, it is required to synchronize the Josephson plasma oscillation in all junctions. In this work, we propose to use two stacks of junctions shunted in parallel to achieve synchronization. The two stacks are mutually synchronized in the whole IV curve, and there is a phase shift between the plasma oscillation in the two stacks. The phase shift is nonzero when the number of junctions in different stacks is the same, while it can be arbitrary when the number of junctions is different. This phase shift can be tuned continuously by applying a magnetic field when all the junctions are connected by superconducting wires.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Association between media coverage and prevalence of idiopathic environmental intolerance attributed to electromagnetic field in Taiwan

Highlights: • The prevalence rate of IEI-EMF in Taiwan declined form 13.3% in 2007 to 4.6% in 2012. • Residents in Taiwan had increasing exposure to EMF related to mobile phone use during the same period of time. • Media coverage of EMF related issues had the similar trend with the decreased IEI-EMF prevalence rate. • Most media coverage conveyed information on the negative health impacts of EMF. • Risk communications seem to be more effective than precautionary measures in coping with the public fears about EMF. Idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF) describes symptoms sufferers attribute to exposure to electromagnetic fields (EMF). In Taiwan, the prevalence rate of IEI-EMF was 13.3% in 2007, but a survey using the same method found the rate declined to 4.6% in 2012. Because media reports may encourage readers to attribute their symptoms to EMF, the change might be related to media coverage. We searched articles indexed in the largest newspaper database in Taiwan to evaluate the association between media coverage and the prevalence of IEI-EMF. We also assessed the effects of other potential affecting factors. The number of newspaper articles related to EMF and IEI-EMF increased from 2005 to 2007 and then has been decreasing until 2012, which is compatible with the change in the prevalence of IEI-EMF. However, from 2007 to 2012, the other potential affecting factors such as density of mobile phone base stations, number of mobile phone users, total mobile phone calling time, and number of text messages sent through mobile phones all increased in Taiwan. This finding indicated a positive association between media coverage and the prevalence of IEI-EMF in Taiwan, which might also be true in other countries.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2019

Differences in the Impurity Ionization in Quasi-Classically Strong Constant and Alternating Electric Fields in a Two-Dimensional Superlattice Based on Graphene

The coefficient of the absorption of an electromagnetic wave in a two-dimensional superlattice based on graphene, in the presence of a constant electric field for the case of quasi-classically strong electric fields is investigated. The anisotropy of the absorption coefficient is revealed at different orientations of the vector of the constant electric field and the vector of polarization of the alternating electric field. It is demonstrated that the slow increase in the absorption coefficient at low frequencies is caused by impurity absorption, and its faster increase at higher frequencies is determined by miniband-to-miniband transitions. These peculiar properties can be used for the development of radiation detectors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2008

Environmental Assurance Program for the Phoenix Mars Mission

The Phoenix Mars mission involves delivering a stationary science lander on to the surface of Mars in the polar region within the latitude band 65 deg N to 72 deg N. Its primary objective is to perform in-situ and remote sensing investigations that will characterize the chemistry of the materials at the local surface, subsurface, and atmosphere. The Phoenix spacecraft was launched on August 4, 2007 and will arrive at Mars in May 2008. The lander includes a suite of seven (7) science instruments. This mission is baselined for up to 90 sols (Martian days) of digging, sampling, and analysis. Operating at the Mars polar region creates a challenging environment for the Phoenix landed subsystems and instruments with Mars surface temperature extremes between -120 deg C to 25 deg C and diurnal thermal cycling in excess of 145 deg C. Some engineering and science hardware inside the lander were qualification tested up to 80 deg C to account for self heating. Furthermore, many of the hardware for this mission were inherited from earlier missions: the lander from the Mars Surveyor Program 2001 (MSP'01) and instruments from the MSP'01 and the Mars Polar Lander. Ensuring all the hardware was properly qualified and flight acceptance tested to meet the environments for this mission required defining and implementing an environmental assurance program that included a detailed heritage review coupled with tailored flight acceptance testing. A heritage review process with defined acceptance success criteria was developed and is presented in this paper together with the lessons learned in its implementation. This paper also provides a detailed description of the environmental assurance program of the Phoenix Mars mission. This program includes assembly/subsystem and system level testing in the areas of dynamics, thermal, and electromagnetic compatibility, as well as venting/pressure, dust, radiation, and meteoroid analyses to meet the challenging environment of this mission.

thermal testing↗
DOE OSTI2020

The CLAS12 Forward Tagger

This document presents the technical layout and the performance of the CLAS12 Forward Tagger (FT). The FT, composed of an electromagnetic calorimeter based on PbWO$_4$ crystals (FT-Cal), a scintillation hodoscope (FT-Hodo), and several layers of Micromegas trackers (FT-Trk), has been designed to detect electrons and photons scattered at polar angles from 2$^\circ$ to 5$^\circ$ and to meet the physics goals of the hadron spectroscopy program and other experiments running with the CLAS12 spectrometer in Hall B.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Peculiarities of electromagnetic field distribution in a finite one-dimensional photonic crystal at oblique incidence of radiation

The effect of increasing an electric field E is investigated for oblique incidence of radiation on a finite one-dimensional photonic crystal. The peculiarities in the field distribution in the structure E(x) are found to be due to the interference of counterpropagating Bloch waves; therefore, the conditions for increasing the field to a maximum value |E|{sub max} coincide with those for achieving the maximum band gap E{sub g} of an infinite crystal. It is shown that a significant (several times for structures with 30 periods) growth of |E|{sub max} is observed with increasing angle of incidence θ for wavelengths λ, which correspond to transmission maxima T nearest to the band gap boundaries. The increased interference of the counterpropagating Bloch modes is caused by an enhancement of the x-component contrast (perpendicular to the planes of the layers) of the wave numbers k{sub 1x}/k{sub 2x} in the structure layers. Along with this, there also arise characteristic features in the distribution of E(x) associated with the vanishing of the forbidden band width. In this case, the field distribution in all periods is the same. Two types of such features are observed in the case of oblique incidence. The former takes place for p-polarisation at an angle of incidence θ, which is an analogue of the Brewster angle. The latter corresponds to the situation when the length of each structure layer is equal to an integer of half-waves. This occurs simultaneously for s- and p-polarisations and is observed in a limited range of layer widths only for the second and highest forbidden bands. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Probability of radiation of twisted photons in the infrared domain

Highlights: •Infrared asymptotics of twisted photon radiation in QED is studied. •General selection rules for the twisted photon radiation are proved. •Exact formulas for the twisted photon edge radiation are obtained. •Edge radiation is a superradiant source of twisted photons in the infrared domain. -- Abstract: The infrared asymptotics of the probability of radiation of twisted photons in an arbitrary scattering process of quantum electrodynamics in vacuum is investigated. This asymptotics is universal and corresponds to the radiation produced by a classical current. Such radiation is known as edge radiation. We represent it in terms of twisted photons, and exact analytical formulas for the average number of radiated twisted photons are derived. We find the average projection of the total angular momentum of the edge radiation and the angular momentum per photon. It is shown that edge radiation can be used as a source of twisted photons with a large angular momentum. Moreover, this radiation can be employed as a superradiant coherent source of twisted photons in the infrared domain, in particular, the THz part of the electromagnetic spectrum. Several general selection rules for the radiation and absorption of twisted photons are proved. In particular, these selection rules allow one to modulate the one-particle radiation probability by means of scattering of charged particles on symmetrically arranged crystals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1987

Coordinated ultraviolet and radio observations of selected nearby stars

All of the US2 shifts assigned were successfully completed with simultaneous International Ultraviolet Explorer (IUE) and the Very Large Array (VLA) observations of the proposed target stars. The target stars included dwarf M flare stars and RS CVn stars. The combined ultraviolet (IUE) and microwave (VLA) observations have provided important new insights to the radiation mechanisms at these two widely-separated regions of the electromagnetic spectrum. The VLA results included the discovery of narrow-band microwave radiation and rapid time variations in the microwave radiation of dwarf M flare stars. The results indicate that conventional radiation mechanisms cannot explain the microwave emission from these stars. In general, ultraviolet variations and bursts occur when no similar variations are detected at microwave wavelengths and vice versa. Although these is some overlap, the variations in these two spectral regions are usually uncorrelated, suggesting that there is little interaction between the activity centers at the two associated atmospheric levels.

Lang, Kenneth R.↗
DOE OSTI2017

Modeling radiation loads in the ILC main linac and a novel approach to treat dark current

Electromagnetic and hadron showers generated by electrons of dark current (DC) can represent a significant radiation threat to the ILC linac equipment and personnel. In this study, a commissioning scenario is analysed which is considered as the worst-case scenario for the main linac regarding the DC contribution to the radiation environment in the tunnel. A normal operation scenario is analysed as well. An emphasis is made on radiation load to sensitive electronic equipment—cryogenic thermometers inside the cryomodules. Prompt and residual dose rates in the ILC main linac tunnels were also calculated in these new high-statistics runs. A novel approach was developed—as a part of general purpose Monte Carlo code MARS15—to model generation, acceleration and transport of DC electrons in electromagnetic fields inside SRF cavities. Comparisons were made with a standard approach when a set of pre-calculated DC electron trajectories is used, with a proper normalization, as a source for Monte Carlo modelling. Results of MARS15 Monte Carlo calculations, performed for the current main linac tunnel design, reveal that the peak absorbed dose in the cryogenic thermometers in the main tunnel for 20 years of operation is about 0.8 MGy. The calculated contact residual dose on cryomodules and tunnel walls in the main tunnel for typical irradiation and cooling conditions is 0.1 and 0.01 mSv/hr, respectively.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

On refractive processes in strong laser field quantum electrodynamics

Refractive processes in strong-field QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a plane-wave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultra-relativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background plane-wave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strong-field QED at present and next-generation facilities. -- Highlights: •Investigation of the one-loop amplitude of refractive QED processes in a laser field. •The amplitude is suppressed for a large number of net-exchanged laser photons. •Suggestion for first observation of high-nonlinear vacuum effects in a laser field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

The THESEUS space mission concept: science case, design and expected performances

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1sr) with 0.5–1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift ~10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late ’20s/early ’30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. In conclusion, THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Evidence of Sub-MeV EMIC-Driven Trapped Electron Flux Dropouts From GPS Observations

We report that for many years, it was believed that resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons were restricted to electron energies >1–2 MeV. In recent years, however, a growing body of experimental evidence has shown that EMIC waves can cause the scattering loss of electrons down to sub-MeV energies. Using measurements of trapped electron flux from the Global Positioning System satellite constellation, we investigate the ability of EMIC waves to cause significant depletions of radiation belt electron populations between 4 ≤ L* ≤ 5. For the first time, we present statistical evidence demonstrating global decreases in sub-MeV trapped electron flux in response to EMIC wave activity. Although we find that electron losses extend down to sub-MeV energies, we also show strong statistical support for the ability of EMIC waves to preferentially cause substantial depletions of ultra-relativistic electrons in the radiation belts.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Towards higher frequencies in a compact prebunched waveguide THz-FEL

Free-electron-lasers fill a critical gap in the space of THz-sources as they can reach high average and peak powers with spectral tunability. Using a waveguide in a THz FEL significantly increases the coupling between the relativistic electrons and electromagnetic field enabling large amounts of radiation to be generated in a single passage of electrons through the undulator. In addition to transversely confining the radiation, the dispersive properties of the waveguide critically affect the velocity and slippage of the radiation pulse which determine the central frequency and bandwidth of the generated radiation. In this paper, we characterize the spectral properties of a compact waveguide THz FEL including simultaneous lasing at two different frequencies and demonstrating tuning of the radiation wavelength in the high frequency branch by varying the beam energy and ensuring that the electrons injected into the undulator are prebunched on the scale of the resonant radiation wavelength.

Experimental particle physics↗
DOE OSTI2017

Broadband mixing of ${\mathscr{P}}{\mathscr{T}}$-symmetric and ${\mathscr{P}}{\mathscr{T}}$-broken phases in photonic heterostructures with a one-dimensional loss/gain bilayer

Combining loss and gain components in one photonic heterostructure opens a new route to efficient manipulation by radiation, transmission, absorption, and scattering of electromagnetic waves. Therefore, loss/gain structures enabling $${\mathscr{P}}{\mathscr{T}}$$-symmetric and $${\mathscr{P}}{\mathscr{T}}$$-broken phases for eigenvalues have extensively been studied in the last decade. In particular, translation from one phase to another, which occurs at the critical point in the two-channel structures with one-dimensional loss/gain components, is often associated with one-way transmission. In this report, broadband mixing of the $${\mathscr{P}}{\mathscr{T}}$$-symmetric and $${\mathscr{P}}{\mathscr{T}}$$-broken phases for eigenvalues is theoretically demonstrated in heterostructures with four channels obtained by combining a one-dimensional loss/gain bilayer and one or two thin polarization-converting components (PCCs). The broadband phase mixing in the four-channel case is expected to yield advanced transmission and absorption regimes. Various configurations are analyzed, which are distinguished in symmetry properties and polarization conversion regime of PCCs. The conditions necessary for phase mixing are then discussed. The simplest two-component configurations with broadband mixing are found, as well as the more complex three-component configurations wherein symmetric and broken sets are not yet mixed and appear in the neighbouring frequency ranges. Peculiarities of eigenvalue behaviour are considered for different permittivity ranges of loss/gain medium, i.e., from epsilon-near-zero to high-epsilon regime.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Terahertz field enhancement via coherent superposition of the pulse sequences after a single optical-rectification crystal

Terahertz electromagnetic pulses are frequently generated by optical rectification of femtosecond laser pulses. In many cases, the efficiency of this process is known to saturate with increasing intensity of the generation beam because of two-photon absorption. Here, we demonstrate two routes to reduce this effect in ZnTe(110) crystals and enhance efficiency, namely, by (i) recycling the generation pulses and by (ii) splitting each generation pulse into two pulses before pumping the crystal. In both methods, the second pulse arrives ∼1 ns after the first one, sufficiently long for optically generated carriers to relax. Enhancement is achieved by coherently superimposing the two resulting terahertz fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Femtosecond-laser hyperdoping silicon in an SF{sub 6} atmosphere: Dopant incorporation mechanism

In this paper, we examine the fundamental processes that occur during femtosecond-laser hyperdoping of silicon with a gas-phase dopant precursor. We probe the dopant concentration profile as a function of the number of laser pulses and pressure of the dopant precursor (sulfur hexafluoride). In contrast to previous studies, we show the hyperdoped layer is single crystalline. From the dose dependence on pressure, we conclude that surface adsorbed molecules are the dominant source of the dopant atoms. Using numerical simulation, we estimate the change in flux with increasing number of laser pulses to fit the concentration profiles. We hypothesize that the native oxide plays an important role in setting the surface boundary condition. As a result of the removal of the native oxide by successive laser pulses, dopant incorporation is more efficient during the later stage of laser irradiation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗