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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simulation of stellarator divertors

The nested magnetic surfaces that confine a fusion plasma can be developed to be bounded by a limiter or a divertor. For a limiter, confining surfaces extend until they intercept a part of the surrounding structure. For a divertor, an outermost confining magnetic surface exists, which is well separated from the surrounding structures. The only designs that are thought to be fusion relevant have divertors that direct field lines from the plasma edge into chambers where the particle exhaust can be pumped and the residual heat exhaust can be handled. The topological properties of magnetic field lines just outside the outermost confining surface determine much of the physics of divertors. Axisymmetric tokamak divertors are well-known, and the outermost confining surface is defined by a sharp separatrix. The topology of the magnetic field lines associated with a stellarator divertor is far more subtle. Related subtleties arise in tokamak divertors when subjected to sufficiently strong non-axisymmetric perturbations.Here, an efficient simulation method for carrying out topological studies of non-axisymmetric divertors is created and illustrative results are given.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ∼ 10{sup 7} − 10{sup 10} G and rotate very fast with angular frequencies Ω ∼ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission “o2” is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Electric field effects during disruptions

Tokamak disruptions are associated with breaking magnetic surfaces, which makes magnetic field lines chaotic in large regions of the plasma. The enforcement of quasi-neutrality in a region of chaotic field lines requires an electric potential that has both short and long correlation distances across the magnetic field lines. The short correlation distances produce a Bohm-like diffusion coefficient ∼Te/eB and the long correlation distances aT produce a large scale flow ∼Te/eBaT. This cross-field diffusion and flow are important for sweeping impurities into the core of a disrupting tokamak. The analysis separates the electric field in a plasma into the sum of a divergence-free, E→B, and a curl-free, E→q, part, a Helmholtz decomposition. The divergence-free part of E→ determines the evolution of the magnetic field. The curl-free part enforces quasi-neutrality, E→q=−∇→Φq. Magnetic helicity evolution gives the required boundary condition for a unique Helmholtz decomposition and an unfortunate constraint on steady-state tokamak maintenance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Appearances and statistics of coronal cavities during the ascending phase of solar cycle 24

We present a survey of 429 coronal prominence cavities found between 2010 May and 2015 February using the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly limb synoptic maps. We examined correlations between each cavity’s height, width, and length. Our findings showed that around 38% of the cavities were prolate, 27% oblate, and 35% circular in shape. The lengths of the cavities ranged from 0.06 to 2.9 R{sub ⊙}. When a cavity is longer than 1.5 R{sub ⊙}, it has a narrower height range (0.1–0.3 R{sub ⊙}), whereas when the cavity was shorter than 1.5 R{sub ⊙}, it had a wider height range (0.07–0.5 R{sub ⊙}). We find that the overall three-dimensional topology of the long, stable cavities can be characterized as a long tube with an elliptical cross section. We also noted that the circular and oblate cavities are longer in length than the prolate cavities. We also studied the physical mechanisms behind the cavity drift toward the pole and found it to be tied to the meridional flow. Finally, by observing the evolution of the cavity regions using SDO/Helioseismic Magnetic Imager (HMI) surface magnetic field observations, we found that the cavities formed a belt near the polar coronal hole boundary; we call this the cavity belt. Our results showed that the cavity belt migrated toward higher latitude over time and the cavity belt disappeared after the polar magnetic field reversal. This result shows that cavity evolution provides new insight into the solar cycle.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

Stellar coronae from Einstein - Observations and theory

Einstein Observatory observations of stellar X-ray emission are presented and their implications for the formation of stellar coronae and the problem of stellar angular momentum loss are discussed. Solar coronal X-ray observations and observations of stellar coronae made prior to Einstein are reviewed, and it is noted that they already suggest that the standard theory of acoustic coronal heating is inadequate. The principal results of the Einstein/CfA stellar survey are summarized, with attention given to variations of the level of X-ray flux detected along the main sequence, the decline of X-ray flux with increasing age of giants and supergiants, and indications of a large range of X-ray emission levels within a given type, which are clearly incompatible with models for acoustic flux generation. A new theory to explain stellar coronae and hence X-ray emission from them is then proposed in which stellar magnetic fields play the key role in determining the level of coronal emission, and the modulation of the surface magnetic flux level and the level of stressing of surface magnetic fields essentially determine the variation of mean coronal activity in the H-R diagram.

Rosner, R.↗
DOE OSTI2018

A Prototype Dual Robot System to Perform Ultrasonic and Visual Inspection for the Bottom of Double-Shell Tanks - 18624

Up to this point, ultrasonic inspection-based condition data has only been available for double-shell tank (DST) sidewalls because direct inspection access to the primary tank bottom is limited to vent duct channels in an insulating refractory pad that the primary tank rests on. Probe access through the air slot would provide the opportunity to get information about the condition of the bottom of the primary tank, but it is a challenge to deploy a crawling robot that is capable of performing nondestructive ultrasonic and visual inspection through confined air slots. As such, a conceptual prototype of a deployable inspection robot system to enable ultrasonic and visual inspection for DST base through ventilation ducts was designed and fabricated. This prototype dual robot system consisting of the AnnulusBot and the MouseBot can be integrated with nondestructive evaluation (NDE) sensors to inspect and examine the physical properties of the underside of DSTs to enable status assessment. The AnnulusBot was designed to carry the MouseBot and to be deployed to the annulus space through a riser. To deploy the MouseBot to every ventilation channel in the annulus, the arm consisting of a boom and a forearm was used to place the MouseBot on the underside of the tank. The AnnulusBot used segmented wheels enable to traverse pipes and other potential obstacles. The cable management system utilized motorized wheels to feed the cable into the ventilation channel. This would reduce the amount of work that the MouseBot would have to do during inspection. This feeding mechanism would also be used to retrieve the MouseBot at the end of its inspection. Additionally, if the MouseBot fails, this mechanism would be used for retrieval. Once deployed, the MouseBot navigates to the center of the tank via the air ventilation channel beneath the inner shell (the primary tank) while inspecting the space. The MouseBot is then retrieved from the channel by a combination of its own drive power and the AnnulusBot retracting the attached umbilical cord. Compare with the AnnulusBot, the physical dimensional limitations of the MouseBot were a greater challenge. As the surface state of the concrete of the air channels could have variable texture, and may contain debris, it was decided not to travel along this surface. The ceiling of these channels is carbon steel and can be utilized throughout the channel. To use this travel surface, magnetic wheels were employed. A foreseeable problem with the use of magnets on this surface, is that they would preclude the use of eddy currents sensors. However, other technologies like ultrasonic technology sensors should be unaffected. Laboratory scale test was performed on a mock-up single wedge of the refractory pad to evaluate maneuverability of the MouseBot. The electronic components for the prototype would work in the ranges of 150-185 deg. F (65.6-85 deg. C). Both the AnnulusBot and MouseBot will be subject to constant radiation. All major printed circuit board (PCB) microcontroller components were designed to be situated outside of the annulus space and inside the main control panel to avoid radiation-induced failure. As future work, electronic components including the Arduinos that used Atmel commercial microcontrollers will be replaced with the high temperature rated Atmel microcontrollers so that the robots can be operated reliably at ambient temperatures up to 200 deg. F (93.3 deg. C). In addition, the robots will be service life tested to evaluate performance at elevated temperature and under gamma irradiation. (authors)

42 ENGINEERING↗
DOE OSTI2017

Runaway electrons and ITER

The potential for damage, the magnitude of the extrapolation, and the importance of the atypical—incidents that occur once in a thousand shots—make theory and simulation essential for ensuring that relativistic runaway electrons will not prevent ITER from achieving its mission. Most of the theoretical literature on electron runaway assumes magnetic surfaces exist. ITER planning for the avoidance of halo and runaway currents is focused on massive gas or shattered-pellet injection of impurities. In simulations of experiments, such injections lead to a rapid large-scale magnetic-surface breakup. Surface breakup, which is a magnetic reconnection, can occur on a quasi-ideal Alfvénic time scale when the resistance is sufficiently small. Nevertheless, the removal of the bulk of the poloidal flux, as in halo-current mitigation, is on a resistive time scale. The acceleration of electrons to relativistic energies requires the confinement of some tubes of magnetic flux within the plasma and a resistive time scale. The interpretation of experiments on existing tokamaks and their extrapolation to ITER should carefully distinguish confined versus unconfined magnetic field lines and quasi-ideal versus resistive evolution. The separation of quasi-ideal from resistive evolution is extremely challenging numerically, but is greatly simplified by constraints of Maxwell’s equations, and in particular those associated with magnetic helicity. Thus, the physics of electron runaway along confined magnetic field lines is clarified by relations among the poloidal flux change required for an e-fold in the number of electrons, the energy distribution of the relativistic electrons, and the number of relativistic electron strikes that can be expected in a single disruption event.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Plasma current resonance in asymmetric toroidal systems

The well-known singularity in the magnetic differential equation for plasma current in an asymmetric toroidal confinement system is resolved by including in the pressure tensor corrections stemming from finite Larmor radius. The result provides an estimate of the amplitude of spikes in the parallel current that occur on rational magnetic surfaces. Further, resolution of the singularity is shown to depend on both the ambipolarity condition—the requirement of zero surface-averaged radial current—and the form of the magnetic differential equation near the rational surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

High surface area magnetic double perovskite La 2 AlFeO 6 as an efficient and stable photo-Fenton catalyst under a wide pH range

Photo-Fenton process is an efficient way to treat the organic pollutants in wastewater. However, the efficiency is limited by serious leaching of iron ion, separation of spent catalyst from reaction system for facile recycling, low (pH<4) reaction environment. Herein, we report a preparation of a novel magnetic double perovskite photocatalyst La2AlFeO6, and refractory organic pollutants like phenol, etc. were used as probes to test the efficiency of catalyst. The results showed that the catalytic material retained high surface area and high ratio of Fe 3+ on its surface, and the generated ·OH, ·O 2 - and 1 O 2 lead to a highly photocatalytic efficiency even at neutral pH condition. In addition, the as prepared double perovskite photocatalyst La 2 AlFeO 6 also exhibits excellent stable and magnetic properties. There is no iron ion leaching detected during the courses of the reaction. Furthermore, the spent catalyst can be separated by magnetic field easily, and thus can be reused after simple air drying without any further treatment or calcination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Bulk and element-specific magnetism of medium-entropy and high-entropy Cantor-Wu alloys

Magnetic Compton scattering, x-ray magnetic circular dichroism spectroscopy, and bulk magnetometry measurements are performed on a set of medium- (NiFeCo and NiFeCoCr) and high-entropy (NiFeCoCrPd and NiFeCoCrMn) Cantor-Wu alloys. The bulk spin momentum densities determined by magnetic Compton scattering are remarkably isotropic, and this is a consequence of the smearing of the electronic structure by disorder scattering of the electron quasiparticles. Nonzero x-ray magnetic circular dichroism signals are observed for every element in every alloy indicating differences in the populations of the majority and minority spin states implying finite magnetic moments. When Cr is included in the solid solution, the Cr spin moment is unambiguously antiparallel to the total magnetic moment, while a vanishingly small magnetic moment is observed for Mn, despite calculations indicating a large moment. Some significant discrepancies are observed between the experimental bulk and surface magnetic moments. Furthermore, despite the lack of quantitative agreement, the element-specific surface magnetic moments seem to be qualitatively reasonable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Extraordinary phase transition revealed in a van der Waals antiferromagnet

While the surface-bulk correspondence has been ubiquitously shown in topological phases, the relationship between surface and bulk in Landau-like phases is much less explored. Theoretical investigations since 1970s for semi-infinite systems have predicted the possibility of the surface order emerging at a higher temperature than the bulk, clearly illustrating a counterintuitive situation and greatly enriching phase transitions. But experimental realizations of this prediction remain missing. Here, we demonstrate the higher-temperature surface and lower-temperature bulk phase transitions in CrSBr, a van der Waals (vdW) layered antiferromagnet. We leverage the surface sensitivity of electric dipole second harmonic generation (SHG) to resolve surface magnetism, the bulk nature of electric quadrupole SHG to probe bulk spin correlations, and their interference to capture the two magnetic domain states. Our density functional theory calculations show the suppression of ferromagnetic-antiferromagnetic competition at the surface is responsible for this enhanced surface magnetism. Our results not only show counterintuitive, richer phase transitions in vdW magnets, but also provide viable ways to enhance magnetism in their 2D form.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, George Williams College, Lake Geneva, Wis., September 30-October 4, 1974, Proceedings

The papers deal with solar-wind and magnetospheric interactions with the moon, ancient and present-day lunar surface magnetic and electric fields, the dynamics and evolution of the lunar atmosphere, the lunar record of solar radiation, and nonmeteoric transport of lunar surface materials. Topics discussed include bow-shock protons in the lunar environment, energetic ion events during the lunar night, mapping of the lunar surface magnetic field from orbital observations of mirrored electrons, geomagnetic disturbances induced by the moon, the relationship between lunar topography and limb compressions, measurements of lunar sky brightness, atmospheric supply and loss mechanisms on the moon, the nature and composition of the lunar atmosphere, molecular gas species in that atmosphere, and vacuum-UV spectroscopic measurements of the surface properties of lunar materials. Individual items are announced in this issue.

Source record↗
NASA NTRS2012

Broadband Spectral Investigations of SGR J1550-5418 Bursts

We present the results of our broadband spectral analysis of 42 SGR J1550−5418 bursts simultaneously detected with the Swift/X-ray Telescope (XRT) and the Fermi/Gamma-ray Burst Monitor (GBM), during the 2009 January active episode of the source. The unique spectral and temporal capabilities of the XRT windowed timing mode have allowed us to extend the GBM spectral coverage for these events down to the X-ray domain (0.5-10 keV). Our earlier analysis of the GBM data found that the SGR J1550−5418 burst spectra were described equally well with either a Comptonized model or with two blackbody functions; the two models were statistically indistinguishable. Our new broadband (0.5-200 keV) spectral fits show that, on average, the burst spectra are better described with two blackbody functions than with the Comptonized model. Thus, our joint XRT-GBM analysis clearly shows for the first time that the SGR J1550−5418 burst spectra might naturally be expected to exhibit a more truly thermalized character, such as a two-blackbody or even a multi-blackbody signal. Using the Swift and RXTE timing ephemeris for SGR J1550−5418 we construct the distribution of the XRT burst counts with spin phase and find that it is not correlated with the persistent X-ray emission pulse phase from SGR J1550−5418. These results indicate that the burst emitting sites on the neutron star need not to be co-located with hot spots emitting the bulk of the persistent X-ray emission. Finally, we show that there is a significant pulse phase dependence of the XRT burst counts, likely demonstrating that the surface magnetic field of SGR J1550−5418 is not uniform over the emission zones, since it is anticipated that regions with stronger surface magnetic field could trigger bursts more efficiently.

bursts↗
DOE OSTI2020

Multi-metallic conduction cooled superconducting radio-frequency cavity with high thermal stability

Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and with cooling by a liquid helium bath at a temperature of ~2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator make the current cavity technology not favorable for use in industrial-type accelerators. We have developed a multi-metallic 1.495 GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ~2 µm thick layer of Nb 3 Sn on the inner surface, exposed to the rf field, deposited on a ~3 mm thick bulk Nb shell and a bulk Cu shell, of thickness $\geqslant\! 5$ mm deposited on the outer surface by electroplating. A bolt-on Cu plate 1.27 cm thick was used to thermally connect the cavity equator to the second stage of a Gifford-McMahon cryocooler with a nominal capacity of 2 W at 4.2 K. The cavity was tested initially in liquid helium at 4.3 K and reached a peak surface magnetic field of ~36 mT with a quality factor of 2 × 10 9 . The cavity cooled by the cryocooler achieved a peak surface magnetic field of ~29 mT, equivalent to an accelerating gradient of 6.5 MV m –1 . The conduction-cooled cavity could be operated in continuous-wave with as high as 5 W dissipation in the cavity for 1 h without any thermal breakdown, because of the Cu outer layer with high thermal conductivity. This result represents a paradigm shift in the technology of superconducting accelerator cavities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Enhancements Of Interior Flux In Magnetic Bodies & Exterior Surface Fields On Conducting Objects Of Various Shapes

The magnetic flux induced in magnetic bodies of several shapes are examined. In addition the surface magnetic field intensity on the exterior surface of conducting objects is estimated since it is the driver for narrow slot aperture inductive ports of entry. In this report lower frequencies are the focus, but we also include the magnetic field intensity of a conducting cylinder near the first resonance and a reference to the high frequency limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2002

Chandra Observations of Magnetic White Dwarfs and Their Theoretical Implications

Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is strong observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. Since these fields are likely to be generated by dynamo action and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs.

Musielak, Z. E.↗
NASA NTRS2003

Chandra Observations of Magnetic White Dwarfs and their Theoretical Implications

Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission, but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is some observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. It has been suggested that such fields can be generated by dynamo action, and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs. Another important implication of our negative Chandra observations is the possibility that the magnetic fields of LHS 1038 and GD 358 are fossil fields.

Musielak, Z. E.↗
DOE OSTI2024

Core electron temperature turbulence and transport during sawtooth oscillations in the DIII-D tokamak

Abstract Sawteeth are one of the concerning instabilities in ITER and future burning plasma experiments. Sawtooth dynamics and its interaction with broadband plasma turbulence has been a challenge for predictive simulations of core transport in future fusion devices. This study provides new observations of core turbulence behavior during sawtooth oscillations in DIII-D hydrogen L-mode neutral beam injection heated plasmas in an inner wall limited configuration. A strong correlation of electron temperature and density turbulence levels with the sawtooth oscillation phase has been observed at locations inside the T e inversion radius and/or safety factor q = 1 magnetic surface. The T e turbulence amplitude in the core during the sawtooth ramp exhibits a critical T e gradient behavior inside but not near the T e inversion radius/ q = 1 magnetic surface. The most unstable mode calculated from the trapped gyro-landau fluid turbulence simulations reveal a change from low- k ion-type to low-k electron-type modes from pre- to post- sawtooth crash time periods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗