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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Where was the Iron Synthesized in Cassiopeia A?

We investigate the properties of Fe-rich knots on the east limb of the Cassiopeia A supernova remnant observed with Chandra/AXAF CCD Imaging Spectrometer (ACIS). Using analysis methods developed in a companion paper, we constrain the ejecta density profile and the Lagrangian mass coordinates of the knots from their fitted ionization age and electron temperature. Fe-rich knots which also have strong emission from Si, S, Ar, and Ca are clustered around mass coordinates q approx. equal to 0.35 - 0.4 in the shocked ejecta of 2 solar masses; this places them 0.7 - 0.8 solar masses out from the center (or 2 - 2.1 solar masses, allowing for the mass of a compact object). We also find an Fe clump that is evidently devoid of line emission from lower mass elements, as would be expected for a region that had undergone alpha-rich freeze out. This clump has a similar mass coordinate to the other Fe knots.

Hwang, Una↗
DOE OSTI2022

The radial phase variation of reversed-shear and toroidicity-induced Alfvén eigenmodes in DIII-D

The eigenfunction of an instability contains information about energy flow in the wave. Here, the amplitude and phase of electron cyclotron emission radiometer data from hundreds of DIII-D reversed shear Alfvén eigenmodes (RSAE) and toroidicity-induced Alfvén eigenmodes (TAE) are analyzed along the outboard horizontal midplane. The radial phase profile can be flat, linearly rising or falling, convex or concave; in other words, a wide variety of shapes is observed. For a particular mode, often the radial phase profile remains approximately constant as the mode evolves in time but sometimes it changes rapidly. Many TAEs and some RSAEs have phase profiles that are rather flat where the mode amplitude is largest but rise steadily by ~2π at large major radius. Rapid phase changes are observed when the frequencies of an RSAE and TAE overlap and the modes couple. The phase profile depends weakly on the fast-ion gradient that would appear in the absence of wave-induced transport. Linear and quadratic fits to the phase profiles, together with many plasma parameters, are assembled into RSAE and TAE databases. In both cases, large variability is observed. For RSAEs, the strongest phase dependencies are on electron temperature T e , RSAE mode frequency, and the density of carbon impurities. For TAEs, the strongest dependencies are on beam power and major radius of the mode. In general, the average RSAE radial phase profile is essentially flat but the TAE profile has non-zero slope and curvature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

First lower hybrid current drive experiments on the WEST tokamak

The first lower hybrid current drive experiments in the full tungsten WEST tokamak are reported. Good wave coupling is found at rather low plasma current (q 95 ~4.3) and medium density (n e ~3×10 19 m -3 ). Reflection coefficient is in agreement with the expectation from the linear theory of coupling. With low reflection coefficients, 5MW was coupled for 2 seconds. High central electron temperature, up to 5keV, is achieved at ne = 3-4×10 19 m -3 . Flat and even hollow profiles of tungsten density are derived from the bolometry diagnostic. The stored thermal energy follows the H96-P scaling law with very slight degradation with density. The current drive efficiency has been assessed in low loop voltage (V L ~0.15V) discharges. Low plasma current operation and rather high effective charge (Z eff ~3) lead to modest current drive efficiency (η = 0.5-0.65 × 10 19 A.W -1 m -2 ). Long pulse operation (~30s) with high LHCD power (P LH =2.7MW) is achieved with stationary parameters, in particular electron and impurity densities, with the upper water-cooled tungsten divertor.

Goniche, M.↗
NASA NTRS1989

The long-term behavior of the main peak of the dayside ionosphere of Venus during solar cycle 21 and its implications on the effect of the solar cycle upon the electron temperature in the main peak region

Results are presented on the long-term behavior of the main peak electron density in the Venus ionosphere during the solar cycle 21, based on 104 radio occultation measurements of the vertical electron density profile in the dayside ionosphere of Venus carried out aboard the Pioneer Venus Orbiter spacecraft (along with published data on 11 Venera 9-10 measurements). The equation representing the electron temperature at h = 140 km is presented. The results imply that the electron temperature at h = 140 km decreased by about 25 percent from solar maximum to solar minimum, compared to a decrease of 50-75 percent above 200 km found by Kliore and Mullen (1989).

Kliore, Arvydas J.↗
NASA NTRS2014

Power Dependence of the Electron Mobility Profile in a Hall Thruster

The electron mobility profile is estimated in a 4.5 kW commercial Hall thruster as a function of discharge power. Internal measurements of plasma potential and electron temperature are made in the thruster channel with a high-speed translating probe. These measurements are presented for a range of throttling conditions from 150 - 400 V and 0.6 - 4.5 kW. The fluid-based solver, Hall2De, is used in conjunction with these internal plasma parameters to estimate the anomalous collision frequency profile at fixed voltage, 300 V, and three power levels. It is found that the anomalous collision frequency profile does not change significantly upstream of the location of the magnetic field peak but that the extent and magnitude of the anomalous collision frequency downstream of the magnetic peak does change with thruster power. These results are discussed in the context of developing phenomenological models for how the collision frequency profile depends on thruster operating conditions.

Jorns, Benjamin A.↗
NASA NTRS2007

TOPLA: A New Empirical Representation of the F-Region Topside and Plasmasphere for the International Reference Ionosphere

The goal of this LWS tools effort is the development of a new data-based F-region TOpside and PLAsmasphere (TOPLA) model for the electron density (Ne) and temperature (Te) for inclusion in the International Reference Ionosphere (IRI) model using newly available satellite data and models for these regions. The IRI model is the de facto international standard for specification of ionospheric parameters and is currently being considered as an ISO Technical Specification for the ionosphere. Our effort is directed towards improving the topside part of the model and extending it into the plasmasphere. Specifically we are planning to overcome the following shortcomings of the current IRI topside model: (I) overestimation of densities above 700 km by a factor of 2 and more, (3) unrealistically steep density profiles at high latitudes during very high solar activities, (4) no solar cycle variations and no semi-annual variations for the electron temperature, (5) discontinuities or unphysical gradients when merging with plasmaspheric models. We will report on first accomplishments and on the current status of the project.

Bilitza, D.↗
NASA NTRS2005

Cusp Dynamics-Particle Acceleration by Alfven Waves

Successful results were obtained from this research project. This investigation answered and/or made progresses on each of the four important questions that were proposed: (1) How do Alfven waves propagate on dayside open field lines? (2) How are precipitating electrons influenced by propagating Alfven waves? (3) How are various cusp electron distributions generated? (4) How are Alfven waves modified by electrons? During the first year of this investigation, the input parameters, such as density and temperature altitude profiles, of the gyrofluid code on the cusp field lines were constructed based on 3-point satellite observations. The initial gyrofluid result was presented at the GEM meeting by Dr. Samuel Jones.

Ergun, Robert E.↗
DOE OSTI2020

Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod

Analysis and modeling of rotation reversal hysteresis experiments show that a single turbulent bifurcation is responsible for the Linear to Saturated Ohmic Confinement (LOC/SOC) transition and concomitant intrinsic rotation reversal on Alcator C-Mod. Plasmas on either side of the reversal exhibit different toroidal rotation profiles and therefore different turbulence characteristics despite the profiles of density and temperature, which are indistinguishable within measurement uncertainty. Elements of this bifurcation are also shown to persist for auxiliary heated L-modes. The deactivation of subdominant (in the linear growth rate and contribution to heat transport) ion temperature gradient and trapped electron mode instabilities is identified as the only possible change in turbulence within a reduced quasilinear transport model across the reversal, which is consistent with the measured profiles and inferred heat and particle fluxes. Experimental constraints on a possible change from strong to weak turbulence, outside the description of the quasilinear model, are also discussed. These results indicate an explanation for the LOC/SOC transition that provides a mechanism for the hysteresis through the dynamics of subdominant modes and changes in their relative populations and does not involve a change in the most linearly unstable ion-scale drift-wave instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

EUV spectra from Skylab /1175-1940 A/ - Mass motions in the transition zone in regions of solar activity

The profiles of spectral lines in the 1100-2000-A range emitted by transition-zone ions in regions of solar activity are discussed. The data were recorded by the NRL spectrograph on Skylab. At the spatial resolution of the Skylab spectrograph (2 x 60 arcsec), it is shown that the line profiles result from the superposed emission of a number of physically distinct regions at different electron densities and with different mass motions. Although high densities are found for some surgelike phenomena at transition-zone temperatures, the densities can also be comparable to normal active-region densities. Line profiles, as well as spectral line intensities, must be considered if meaningful theoretical models of dynamic activity in the transition zone are to be constructed.

Doschek, G. A.↗
DOE OSTI2025

TEM turbulence in simulation and experiment in quasisymmetric and degraded-symmetry configurations of the HSX stellarator

The Helically Symmetric Experiment (HSX) has demonstrated reduced neoclassical transport and flow damping with quasisymmetry, but the difference of turbulent transport between quasisymmetric and degraded-symmetry configurations has not been definitively assessed. Profile analysis presented here shows that anomalous transport at the mid-radius is larger with degraded quasisymmetry when temperature and density profiles are matched. An initial comparison (${T_\mathrm{i}/T_\mathrm{e}} = 1$) between the quasisymmetric and degraded symmetry configurations finds that trapped-electron mode (TEM) turbulence can support larger heat fluxes in the degraded symmetry configuration despite smaller linear growth rates. However, further simulations at the experimental temperature ratio ($T_\mathrm{i}/T_\mathrm{e} = 0.2$) do not reproduce this effect. Experimental measurements of heat transport and density fluctuation amplitude are compared to nonlinear gyrokinetic simulations at the experimental temperature ratio. The heat flux and density fluctuation amplitude in simulation reproduce a substantial dependence on the density gradient, and the simulated heat flux matches measurements within experimental uncertainties, indicating that TEM turbulence is responsible for the anomalous transport at the steep density gradient in HSX.

HSX↗
DOE OSTI2021

Characterization of injection and confinement improvement through impurity induced profile modifications on the Wendelstein 7-X stellarator

Pulsed injections of boron carbide granules into Wendelstein 7-X stellarator (W7-X) plasmas transiently increase the plasma stored energy and core ion temperatures above the reference W7-X experimental programs by up to 30%. In a series of 4 MW electron cyclotron resonance heating experiments, the PPPL Probe Mounted Powder Injector provided 50 ms bursts of 100 μm granules every 350 ms at estimated quantities ranging from approximately 1 mg/pulse to over 30 mg/pulse. For each injection, the stored energy was observed to initially drop and the radiated power transiently increased, while the radial electron density profile rose at the edge as material was assimilated. Once the injected boron carbide was fully absorbed, the density rise transitioned to the core while the stored energy increased above the previous baseline level by an amount linearly correlated with the injection quantity. During the injection, the ion temperature gradient steepened with peak core ion temperatures observed to increase from a nominal 1.7 keV to over 2.6 keV for the largest injection amounts. Enhanced performance is accompanied by a reversal of the radial electric field at ρ < 0.3, indicating that the core transport has switched to the ion root. These observations are suggestive of a change in transport and provide further evidence that externally induced profile modifications provide a possible path to enhanced W7-X performance metrics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Spectroscopic Signatures of Phonon Character in Molecular Electron Spin Relaxation

Spin–lattice relaxation constitutes a key challenge for the development of quantum technologies, as it destroys superpositions in molecular quantum bits (qubits) and magnetic memory in single molecule magnets (SMMs). Gaining mechanistic insight into the spin relaxation process has proven challenging owing to a lack of spectroscopic observables and contradictions among theoretical models. Here, we use pulse electron paramagnetic resonance (EPR) to profile changes in spin relaxation rates (T 1 ) as a function of both temperature and magnetic field orientation, forming a two-dimensional data matrix. For randomly oriented powder samples, spin relaxation anisotropy changes dramatically with temperature, delineating multiple regimes of relaxation processes for each Cu(II) molecule studied. We show that traditional T 1 fitting approaches cannot reliably extract this information. Single-crystal T 1 anisotropy experiments reveal a surprising change in spin relaxation symmetry between these two regimes. We interpret this switch through the concept of a spin relaxation tensor, enabling discrimination between delocalized lattice phonons and localized molecular vibrations in the two relaxation regimes. Variable-temperature T 1 anisotropy thus provides a unique spectroscopic method to interrogate the character of nuclear motions causing spin relaxation and the loss of quantum information.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Analysis of coronal H I Lyman-alpha measurements in a polar region of the sun observed in 1979

Measurements of the intensities and spectral line profiles of resonantly scattered hydrogen Ly-alpha radiation have been used to determine hydrogen kinetic temperatures and electron densities between r = 1.5 and 2.2 solar radii in a polar region of the corona observed in 1979 near solar maximum. The mean temperature, 1.8 x 10 to the 6th K, in this region is significantly higher, by about 60 percent, than that obtained in a similar region observed in a 1980 rocket flight. The densities in these two polar regions are similar and are a factor of about 4 larger than in polar coronal holes observed at solar minimum. The flow velocities in both regions are most likely subsonic for r less than about 4 solar radii. The results reported here support the hypothesis that polar coronal holes observed at different times during the solar cycle can have different temperatures, densities, and possibly flow velocities.

Withbroe, G. L.↗
NASA NTRS2021

Atacama Cosmology Telescope: Combined kinematic and thermal Sunyaev-Zel’dovich measurements from BOSS CMASS and LOWZ halos

The scattering of cosmic microwave background (CMB) photons off the free-electron gas in galaxies and clusters leaves detectable imprints on high resolution CMB maps: the thermal and kinematic Sunyaev-Zel’dovich effects (tSZ and kSZ respectively). We use combined microwave maps from the Atacama Cosmology Telescope DR5 and Planck in combination with the CMASS (mean redshifthzi¼0.55and host halo masshMviri¼3×1013M⊙) and LOWZ (hzi¼0.31,hMviri¼5×1013M⊙) galaxy catalogs from the Baryon Oscillation Spectroscopic Survey (BOSS DR10 and DR12), to study the gas associated with these galaxy groups. Using individual reconstructed velocities, we perform a stacking analysis and reject the no-kSZ hypothes is at 6.5σ, the highest significance to date. This directly translates into a measurement of the electron number density profile, and thus of the gas density profile. Despite the limited signal to noise, the measurement shows at high significance that the gas density profile is more extended than the dark matter density profile, for any reasonable baryon abundance (formally>90σfor the cosmic baryon abundance). We simultaneously measure the tSZ signal, i.e., the electron thermal pressure profile of the same CMASS objects, and reject theno-tSZ hypothesis at10σ. We combine tSZ and kSZ measurements to estimate the electron temperature to20% precision in several aperture bins, and find it comparable to the virial temperature. In a companion paper, we analyze these measurements to constrain the gas thermodynamics and the properties of feedback inside galaxy groups. We present the corresponding LOWZ measurements in this paper, ruling out a null kSZ (tSZ)signal at 2.9ð13.9Þσ, and leave their interpretation to future work. This paper and the companion paper demonstrate that current CMB experiments can detect and resolve gas profiles in low mass halos and at high redshifts, which are the most sensitive to feedback in galaxy formation and the most difficult to measure any other way. They will be a crucial input to cosmological hydrodynamical simulations, thus improving our understanding of galaxy formation. These precise gas profiles are already sufficient to reduce the main limiting theoretical systematic in galaxy-galaxy lensing: baryonic uncertainties. Future such measurements will thus unleash the statistical power of weak lensing from the Rubin, Euclid and Roman observatories. Our stacking software Thumb Stack is publicly available and directly applicable to future Simons Observatory andCMB-S4 data.

Emmanuel Schaan↗
NASA NTRS1979

The energetics of the ionosphere of Venus - A preliminary model based on Pioneer Venus observations

A model of the energy balance of the dayside ionosphere of Venus is presented. The coupled energy equations for electrons and ions are solved numerically and the calculated temperatures are compared with temperatures measured by instruments on the Pioneer Venus Orbiter. Neutral and ion density profiles consistent with those measured by various Pioneer Venus experiments are used in the model. It was found that using standard EUV sources and thermal conductivities the calculations produce temperatures that are much lower than the measured ones. Consequently, further calculations were performed in which (1) the thermal conductivities were inhibited by means of an almost horizontal magnetic field and/or (2) heat inflow into both the electron and ion gas at the top of the ionosphere was assumed due to the solar wind interaction. It was found that the calculated and measured temperatures were in reasonably good agreement if the thermal conductivities were inhibited by a near horizontal field of about 10 gammas and if the electron and ion heat fluxes were taken to be 4 x 10 to the 9th eV/sq cm/sec and 10 to the 7th eV/sq cm/sec, respectively.

Cravens, T. E.↗
NASA NTRS1976

Metastable 2D atomic nitrogen in the mid-latitude nocturnal ionosphere

The only source at night at midlatitudes of N(2D) in the F region is the dissociative recombination of the positive NO ion, and the only important sinks are quenching by atomic oxygen and electrons. Ground-based measurements of the 5200 angstrom emission line resulting from the transition from N(2D) to N(4S) combined with satellite observations of neutral and ion densities and temperatures and the shape of the 5200 angstrom profile are used to relate the rate of quenching by atomic oxygen and the efficiency of production of N(2D) to the rate of quenching by electrons. A rate of quenching by atomic oxygen of 1.5-2.5 x 10 to the minus 12th cu cm/s and an efficiency of (0.8-1.0) plus or minus 30% for the production of N(2D) are obtained.

Torr, M. R.↗
NASA NTRS1987

Effect of LID (Registered) processing on the microstructure and mechanical properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo titanium foil-gauge materials

A study was undertaken to determine the mechanical properties and microstructures resulting from Liquid Interface Diffusion (LID -Registered) processing of foil-gauge specimens of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo coated with varying amounts of LID material. In addition, the effects of various elevated temperature exposures on the concentration profiles of the LID alloying elements were investigated, using specimens with a narrow strip of LID material applied to the surface. Room and elevated temperature tensile properties were determined for both coated and uncoated specimens. Optical microscopy was used to examine alloy microstructures, and scanning electron microscopy to examine fracture surface morphologies. The chemical concentration profiles of the strip-coated specimens were determined with an electron microprobe.

Balckburn, Linda B.↗
DOE OSTI2025

Effect of radial pressure corrugations and profile shearing on turbulence in Fusion plasmas

Microturbulence can produce stationary fine-scale radial corrugations on the plasma density and temperature gradients in magnetic confinement fusion devices. We show that these structures play a significant role in regulating turbulent transport. We focus on the pedestal, studying electron-temperature-gradient (ETG) mode destabilisation and saturation in the presence of radial corrugations on the electron temperature gradient that could result from microtearing turbulence. A linear dispersion relation is derived for a shearless slab case, which indicates that in the presence of a sinusoidal background corrugation, each ETG mode splits into three distinct eigenvalues, with one being the original, one being more unstable and one being less unstable. However, despite the presence of more unstable linear modes, nonlinear gyrokinetic simulations of ETG with corrugated background electron temperature show a reduction of fluxes. Our investigation reveals a radial variation of the phase velocity of the modes that is proportional to the diamagnetic drift velocity and the local pressure gradient. The associated profile shearing breaks the turbulent eddies apart, reducing the transport level. This profile shearing resulting from fine-scale pressure corrugations could be a ubiquitous turbulence saturation mechanism not just in Fusion plasmas, but in Astrophysics and other areas.

FOS: Physical sciences↗