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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Design of a broadband, high-power, off-axis spiral polarization reflector

Spirally polarized beams are known to produce a strong longitudinal field under high numerical aperture focusing. Here, we report on the design of a reflective optical element with an off-axis geometry that is capable of transforming a uniformly polarized beam into a predominantly spirally polarized beam. By utilizing the retardance present in Fresnel reflection, our device can operate over a broad range of wavelengths. The output polarization and intensity structure of a beam passing through the reflector are calculated using polarization and scalar ray tracing. Vector diffraction is used to calculate the polarization and intensity structure under $f/0.656$ focusing. The off-axis reflective design is well-suited for high-power laser applications and could enable current and future laser-based particle accelerators to achieve strong longitudinal fields at focus.

Black, A. Nicholas [Univ. of Rochester, NY (United↗
DOE OSTI2023

Characterizing non-polarization-maintaining highly nonlinear fiber toward squeezed-light generation

Squeezed light, which is easily degraded by loss, could benefit from generation directly in optical fiber. Furthermore, highly nonlinear fiber could offer more efficient generation with lower pump power and shorter fiber lengths than standard single-mode fiber. We investigate non-polarization-maintaining highly nonlinear fiber (HNLF) for squeezed-light generation by characterizing possible sources of excess noise, including its zero-dispersion wavelength (ZDW) variation and polarization noise. We find significant ZDW variation and excess polarization noise. We believe the polarization noise is from non-linear polarization-mode dispersion. We model this polarization noise and find that it is likely to degrade Kerr squeezing but not squeezing from four-wave mixing.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Polarized electron injector for positron production at CEBAF

As a part of the effort to expand the capabilities of CE-BAF 12 GeV (Continuous Electron Beam Accelerator Facility) at Jefferson Lab, the addition of a polarized positron source is considered. This capability would provide acceleration of high duty-cycle polarized posi-trons, with spin >60% polarization, through the same main CEBAF accelerator machine with appropriate mag-net field reversals and linac phasing to the four CEBAF experimental halls. To produce this positron beam, a high average current (3-10 mA) highly polarized electron beam with energy of 100 ? 150 MeV is required at the positron source target. The focus of this paper is the de-sign of that polarized electron beam injector. We will describe the production and delivery of a >3 mA highly polarized electron beam. We will discuss different aspects of the design, the photocathode gun, beam dynamics simulation results, spin manipulation, bunching and accelerating process and final electron beam parameters.

Kazimi, R.↗
DOE OSTI2023

Laser-Induced Polarization for the Electron-Ion Collider

The use of an intense ultrashort laser pulse to induce electron polarization has been proposed in existing literature. Utilizing the Python programming language, a code has been developed to recreate the local constant crossed field approximation (LCFA) with the aim of determining values for transverse polarization given a nonzero initial polarization. It has been shown that over multiple laser shots, lower values of the quantum efficiency parameter are associated with higher transverse polarization output, yet require a greater number of shots to attain maximal polarization. Moreover, the quantum efficiency parameter has been rede fined as a function of intensity for Ti:sapphire laser necessary to induce polarization in the Electron-Ion Collider.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Early Stages in the Lifecycle of Polar Liquid-Bearing Clouds

Stratiform liquid-bearing clouds are ubiquitous over the polar regions, where they are predominantly mixed-phase. These polar clouds induce substantial radiative forcing on the surface and continuously modify the atmospheric thermodynamic budget, with direct implications for the polar ice pack resilience. However, the physical representation of these clouds is still a major challenge for climate models. A significant part of polar liquid-bearing cloud lifecycle is often manifested in a quasi-steady self-sustaining, persistent, and turbulent state, which is driven by longwave cloud radiative cooling and can last for multiple days. This self-sustaining cloud lifecycle stage has been thoroughly investigated in numerous studies, though some of its aspects such as precipitation still lack robust quantification and evaluation. The preceding cloud lifecycle stages, which may last up to several hours, have nonetheless remained widely overlooked. These preceding stages initiate at cloud formation, often in a stable and non-turbulent atmospheric layer and serve as a key junction between cloud persistence and cloud dissipation. These two contrasting cloud lifecycle trajectories pose the question if general circulation models (GCMs) can capture the full lifecycle accurately for the real physical reasons, a necessary condition to improve our confidence in climate projections given the changing polar climate. The purpose of this project was to improve the characterization and understanding of these early stages in the lifecycle of polar stratiform liquid-bearing cloud and to aid their representation in GCMs. This research relied on measurements from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) field campaign, as well as the observations from the ARM West Antarctic Radiation Experiment (AWARE) and the permanent ARM site at Utqiagvik, North Slope of Alaska (NSA).

58 GEOSCIENCES↗
DOE OSTI2023

A High-Magnetic-Field Polarized 3He Target for JLab's CLAS12 Spectrometer

We are developing a polarized 3He target for use in high luminosity electron scattering experiments within the high magnetic field environment of Jefferson Lab's CLAS12 spectrometer. By combining recent advancements in metastability exchange optical pumping (MEOP) of 3He with cryogenic, double-cell target methods as used for the MIT-Bates 88-02 experiment, a target with polarization and gas density comparable to traditional, low-field polarized 3He targets can be reached within high magnetic field environments. We have begun polarizing sealed 3He cells at fields up to 5 T at Jefferson Lab, and are preparing for our first tests exploring polarization performance versus magnetic field and gas pressure in a single cell before we move to the construction of a full, cryogenic, double-cell prototype target. A key focus of our research is the determination of polarization relaxation under the irradiation of an ionizing particle beam within high magnetic fields.

Maxwell, James↗
DOE OSTI2025

AI-Optimized Polarization at Jefferson Lab

The AI-Optimized Polarization project seeks to develop experimental control applications for polarized targets and beams at Jefferson Lab using AI/ML. This paper will focus on two ongoing efforts involving a cryogenic polarized target and a linearly-polarized photon beam. Firstly, cryogenic targets, such as those used in Halls B and C (and approved for Hall D), are complex systems that are sensitive to a number of factors, including the temperature, beam currents, and the microwave and NMR apparatus. Secondly, the Hall D photon beam polarization depends on the optimal orientation of a diamond radiator, which produces coherent bremsstrahlung radiation from the electron beam incident upon it. Manual operation of both systems is tedious and error prone; implementing well-designed, interpretable control systems that incorporate AI is expected to lead to improved real-time polarization. AI optimization of nuclear physics experiments will lead, not just to cost-savings, but also to more efficient and higher-quality data, and this project will help to lay the foundation for future autonomous experiments.

Moran, Patrick [College of William and Mary, Willi↗
DOE OSTI2024

Longitudinal Solid P Longitudinal Solid Polarized Target for CL get for CLAS12 and Study of Spin AS12 and Study of Spin Structure of Nucleons

A suite of experiments measuring target-spin observables in electron-nucleon scattering (dubbed Run Group C) was conducted at Jefferson Lab's Hall B in Newport News, VA with a new polarized nuclear target known as 'APOLLO' (Ammonia POLarized LOngitudinally). This innovative target is engineered to seamlessly integrate with the advanced 12GeV CEBAF (Continuous Electron Beam Accelerator Facility) accelerator and the Hall B CLAS12 (12 GeV CEBAF Large Acceptance Spectrometer) detector array. The 'APOLLO' target harnesses the power of Dynamic Nuclear Polarization (DNP) to achieve longitudinal polarization of solid ammonia, thereby creating a net polarization in both protons (NH3) and deuterons (ND3). These samples are subjected to a 5 Tesla magnetic field produced by the CLAS12 spectrometer central solenoid, cooled to 1 K using helium evaporation, and subsequently exposed to microwave radiation at a frequency of 140 GHz. This project was made possible through a collaborative partnership between the Jefferson Lab Target Group, Old Dominion University, University of Virginia, Christopher Newport University, and the CLAS Collaboration. Integrating the APOLLO target into CLAS12 presented unique challenges because of its specific spatial and dimensional constraints. This dissertation will highlight the innovative solutions developed to address these challenges, including the creation of a new target material transport system, the incorporation of superconducting magnetic correction coils, and the development of a customized Nuclear Magnetic Resonance (NMR) system. In addition to a detailed description of the development and operation of APOLLO, and an overview of RGC, this document also describes the global data fitting of proton asymmetries in the Deep Inelastic scattering (DIS) and the Resonance regions, and it offers insights into the comprehensive analysis of target polarization data.

Pandey, Pushpa↗
DOE OSTI2022

Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer

We present measurements of the polarization of X-rays in the 2–8 keV band from the nucleus of the radio galaxy Centaurus A (Cen A), using a 100 ks observation from the Imaging X-ray Polarimetry Explorer (IXPE). Nearly simultaneous observations of Cen A were also taken with the Swift, NuSTAR, and INTEGRAL observatories. No statistically significant degree of polarization is detected with IXPE. These observations have a minimum detectable polarization at 99% confidence (MDP 99 ) of 6.5% using a weighted, spectral model-independent calculation in the 2–8 keV band. The polarization angle ψ is consequently unconstrained. Spectral fitting across three orders of magnitude in X-ray energy (0.3–400 keV) demonstrates that the SED of Cen A is well described by a simple power law with moderate intrinsic absorption (N H ~ 10 23 cm -2 ) and a Fe Kα emission line, although a second unabsorbed power law is required to account for the observed spectrum at energies below 2 keV. This spectrum suggests that the reprocessing material responsible for this emission line is optically thin and distant from the central black hole. Our upper limits on the X-ray polarization are consistent with the predictions of Compton scattering, although the specific seed photon population responsible for the production of the X-rays cannot be identified. The low polarization degree, variability in the core emission, and the relative lack of variability in the Fe Kα emission line support a picture where electrons are accelerated in a region of highly disordered magnetic fields surrounding the innermost jet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

First-principles-integrated Study of Blazar Synchrotron Radiation and Polarization Signatures from Magnetic Turbulence

Blazar emission is dominated by nonthermal radiation processes that are highly variable across the entire electromagnetic spectrum. Turbulence, which can be a major source of nonthermal particle acceleration, can widely exist in the blazar emission region. The Turbulent Extreme Multi-Zone (TEMZ) model has been used to describe turbulent radiation signatures. Recent particle-in-cell (PIC) simulations have also revealed the stochastic nature of the turbulent emission region and particle acceleration therein. However, radiation signatures have not been systematically studied via first-principles-integrated simulations. In this paper, we perform combined PIC and polarized radiative transfer simulations to study synchrotron emission from magnetic turbulence in the blazar emission region. We find that the multiwavelength flux and polarization are generally characterized by stochastic patterns. Specifically, the variability timescale and average polarization degree (PD) are governed by the correlation length of the turbulence. Interestingly, magnetic turbulence can result in polarization angle swings with arbitrary amplitudes and duration, in either direction, that are not associated with changes in flux or PD. Surprisingly, these swings, which are stochastic in nature, can appear either bumpy or smooth, although large-amplitude swings (>180°) are very rare, as expected. Our radiation and polarization signatures from first-principles-integrated simulations are consistent with the TEMZ model, except that in the latter, there is a weak correlation, with zero lag, between flux and degree of polarization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Modeling the Far-infrared Polarization Spectrum of a High-mass Star-forming Cloud

The polarization spectrum, or wavelength dependence of the polarization fraction, of interstellar dust emission provides important insights into the grain alignment mechanism of interstellar dust grains. We investigate the far-infrared polarization spectrum of a realistic simulated high-mass star-forming cloud under various models of grain alignment and emission. We find that neither a homogeneous grain alignment model nor a grain alignment model that includes collisional dealignment is able to produce the falling spectrum seen in observations. On the other hand, we find that a grain alignment model with grain alignment efficiency dependent on local temperature is capable of producing a falling spectrum that is in qualitative agreement with observations of OMC-1. For the model most in agreement with OMC-1, we find no correlation between the temperature and the slope of the polarization spectrum. However, we do find a positive correlation between the column density and the slope of the polarization spectrum. We suggest this latter correlation to be the result of wavelength-dependent polarization by absorption.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

The optical polarization of Scorpius X-1.

The X-ray source Sco X-1 is known to have a slight linear polarization in visible light. An investigation was conducted to determine whether the origin of the polarization is intrinsic to the source or interstellar. No evidence could be found for unusual polarization properties in Sco X-1 that would point to an intrinsically polarized source, although this cannot be excluded. It is pointed out that the case for interstellar polarization would become very strong if stars in the immediate vicinity are found to be polarized with the same position angle.

Landstreet, J. D.↗
NASA NTRS1972

Interstellar circular polarization.

This paper shows that optical observations of circular polarization produced by aligned interstellar grains could yield valuable information about the grain material. The interstellar medium is known to be linearly dichroic from observations of interstellar linear polarization. Since the same aligned grains make the medium linearly birefringent, a small component of circular polarization can result from incident linearly polarized light if the position angle of the linear polarization does not coincide with either principal axis of the medium. Calculations demonstrate that the wavelength of the circular polarization is sensitive to the imaginary part of the complex refractive index of the grain material. This provides an opportunity of investigating whether the grains are characteristically dielectric or metallic.

Martin, P. G.↗
NASA NTRS1972

High resolution measures of polarization and color of selected lunar areas

High resolution observations of intensity, color (UBV) and polarization were obtained with scanning techniques for a number of lunar areas of special interest, including boundaries of some of the brightest and darkest lunar regions, certain Apollo landing sites and prominent craters. Two dimensional raster scans of colors were obtained for Alphonsus, Aristarchus, and Herodotus. The degree of polarization for any given phase angle appears to be roughly indicative of age. The darker younger mare surface are more highly polarized than the lighter and older mare surfaces, which appear to be more contaminated by lighter material from the highlands or by ray material thrown out from fresh craters. All mare surfaces are more highly polarized than the still older and lighter terra regions surrounding the maria. The very oldest craters are either dark-floored and show polarization characteristics similar to those of the mare surfaces, or if located in the highlands, they are less and less distinguishable from the highland background with greater age, and show the general highland polarization characteristics.

Riley, L. A.↗
NASA NTRS1973

Mariner 9 observations of the surface of Mars in the north polar region.

During the Mariner 9 extended mission the recession of the north polar ice caps was monitored for 130 days. The edge of the cap displayed a peculiar polygonal outline during most of this period. Regional topographic control is suggested as the most likely cause of the polygonality. Whereas densely cratered terrain dominates the south polar region, moderately cratered plains underlie the polar deposits in the north polar region. The mottled cratered plains have been mantled by light deposits located in annular rings south of 70 N. The erosional boundaries between these deposits and the subjacent cratered plains are gradational, show no local topographic relief, and display a spiral serrated circumpolar pattern suggesting eolian erosion. Smooth plains and 'etch-pitted' plains underlie the central polar layered deposits in both polar regions. In addition, these plains have one other morphological variant in the north. Here they display a pattern of very coherent ripple-like waveforms varying in wavelength from several hundred meters to a few kilometers.

Soderblom, L. A.↗
NASA NTRS1973

Interstellar circular polarization and the composition of interstellar dust

This paper shows that optical observations of circular polarization produced by aligned interstellar grains could yield valuable information about the grain material. The interstellar medium is known to be linearly dichroic from observations of interstellar linear polarization; many different grain models using a large variety of compositions can be found to reproduce these observations. Since the same aligned grains make the medium linearly birefringent, a small component of circular polarization can result from incident linearly polarized light if the position angle of the linear polarization does not coincide with either principal axis of the medium. Here calculations are presented to demonstrate that the wavelength of the circular polarization is sensitive to the imaginary part of the complex refractive index of the grain material. This provides an opportunity of investigating whether the grains are characteristically dielectric or metallic. Some possible observations are suggested.

Martin, P. G.↗
NASA NTRS1976

The origin of optical polarization in NGC 1068

The polarization of emission lines in the nucleus of NGC 1068 has been measured with a digicon, a single-channel scanner, and interference filters. It is found that the permitted lines of H and probably also He II are polarized at nearly the same position angle and by the same amount as the neighboring continuum. This argues strongly that a common dust scattering mechanism is responsible for all the polarization. The forbidden lines are weakly polarized at a position angle quite different from the continuum, indicating an origin outside the nuclear scattering region. The continuum radiation has been found to be circularly polarized with ellipticity of the order of 5 percent in the red. Such high ellipticity is very unlikely to be of nonthermal origin. We take it as evidence that the nuclear dust is in the form of clouds in an asymmetric skew geometry; the polarization then arises from multiple scattering within these clouds.

Angel, J. R. P.↗
NASA NTRS1977

EUV analysis of polar plumes

Three polar plumes were studied using Skylab Mg X and O VI data. The plumes lie within the boundaries of a polar coronal hole. We find that the mean temperature of the plumes is about 1.1 million K and that they have a small vertical temperature gradient. Densities are determined and found consistent with white light analyses. The variation of density with height in the plumes is compared with that expected for hydrostatic equilibrium. As is the case for other coronal features, polar plumes will be a source of solar wind if the magnetic field lines are open. On the basis of the derived plume model and estimates of the numbers of plumes in polar coronal holes, it appears that polar plumes contain about 15% of the mass in a typical polar hole and occupy about 10% of the volume.

Ahmad, I. A.↗