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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets

Abstract This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

TOWARD AN EMPIRICAL THEORY OF PULSAR EMISSION. XI. UNDERSTANDING THE ORIENTATIONS OF PULSAR RADIATION AND SUPERNOVA “KICKS”

Two entwined problems have remained unresolved since pulsars were discovered nearly 50 yr ago: the orientation of their polarized emission relative to the emitting magnetic field and the direction of putative supernova “kicks” relative to their rotation axes. The rotational orientation of most pulsars can be inferred only from the (“fiducial”) polarization angle of their radiation, when their beam points directly at the Earth and the emitting polar fluxtube field is ∥ to the rotation axis. Earlier studies have been unrevealing owing to the admixture of different types of radiation (core and conal, two polarization modes), producing both ∥ or ⊥ alignments. In this paper we analyze some 50 pulsars having three characteristics: core radiation beams, reliable absolute polarimetry, and accurate proper motions (PMs). The “fiducial” polarization angle of the core emission, we then find, is usually oriented ⊥ to the PM direction on the sky. The primary core emission is polarized ⊥ to the projected magnetic field in Vela and other pulsars where X-ray imaging reveals the orientation. This shows that the PMs usually lie ∥ to the rotation axes on the sky. Two key physical consequences then follow: first, to the extent that supernova “kicks” are responsible for pulsar PMs, they are mostly ∥ to the rotation axis; and, second, most pulsar radiation is heavily processed by the magnetospheric plasma such that the lowest altitude “parent” core emission is polarized ⊥ to the emitting field, propagating as the extraordinary (X) mode.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Remote-Controlled Removal of Bricks from a Reactor Shaft: An Unconventional Approach - 16406

The first German prototype Fast Breeder Nuclear Reactor (KNK) is currently being dismantled after being the only operating Fast Breeder-type reactor in Germany. The complete dismantling is based on 10 decommissioning permits. Package 3 of the 9. decommissioning permit, which is currently under preparation, comprises the dismantling of the biological shield. Package 2 comprised the dismantling of the Primary Shield. In preparation to lift the 14 primary shield segments on height of the reactor core, these were milled at 16 positions and equipped with a total of 26 holes. As a result of the milling and drilling process, an estimated amount of 500-600 kg cast iron swarfs accumulated at the bottom of the 12 m deep reactor shaft. The cobalt in the cast iron was activated to cobalt-60 during operation. This results in a measurable dose-rate of 30-35 mSv/h. At the conical bottom of the reactor shaft were still the remaining parts of the thermal insulation consisting of a lining with brick stones, covered with loose remnants of the thermal insulation, loose metallic residues and cut-off wheels of the angel grinder. For the next dismantling step, the removal of the activated part of the biological shield, it is necessary that the cast iron swarfs must be removed as well as the remains of the thermal insulation. Firstly, this is necessary to reduce the dose rate inside the shaft for subsequent breakthrough operations and, secondly to have a statically resilient surface for the installation of a necessary working platform for next dismantling tools. There was no access for personnel. A manual removal was also not possible due to the existing dose rate. The cast iron swarfs supposed to be removed by a remote controlled suction unit, which was installed on top of a drum and mounted in a special rack. The complete system was lowered into the reactor shaft by using a crane. After removing the major amount of swarfs, the remaining swarfs as well as the sheet metal liner should be collected with a magnetic grabber. The solution for the metal removal was easy to realize, but there was no idea how to remove the remaining bricks remote controlled out of the reactor shaft. Another boundary was that only existing facilities were supposed to be used in addition to the new suction system, i.e. the existing cranes, gripper, as well as the double lid lock of the encasing for the handling of the vacuum cleaner, the transport of the drum and the lock procedure. The design essentially consists of a suction unit and a collecting unit. Both units are connected hooked by the three single suspension chains on the rack on the traverse and connection of the suction tube. Subsequently the entire unit was drained in the 12 m deep reactor shaft. The entire unit has been lifted out of the reactor shaft and placed on a defined set-down position. At this position, now both of the units could be separated by using the Master-Slave-Manipulator in the encasing (A100). By using different suction pipes the reactor shaft bottom could be exempted from the cast iron swarfs within a few days. The suction unit worked in such a positive way that it was decided to remove the loose refractory bricks, metallic residues, cut off wheels, etc., too. Metal parts remaining on the ground were removed by a magnet. This pragmatic approach avoided additional complex design works and the need of constructing special solutions and thus, massively saved time, cost and dose rate. The duration of planning, permission including implementation amounted to approximately 3 to 4 months. The additional work could be performed directly after the actual dismantling step.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2018

Magnetic Core/Shell Nanocomposites MgFe{sub 2}O{sub 4}/SiO{sub 2} for Biomedical Application: Synthesis and Properties

Magnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe{sub 2}O{sub 4}) is a core, and an amorphous silicon dioxide (silica SiO{sub 2}) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mössbauer spectroscopy. It is found that the MgFe{sub 2}O{sub 4}/SiO{sub 2} MNC has the core/shell structure formed by the Fe‒O–Si chemical bond. After coating with silica, the MgFe{sub 2}O{sub 4}/SiO{sub 2} MNC saturation magnetization significantly decreases in comparison with MgFe{sub 2}O{sub 4} particles without a SiO{sub 2} shell. Spherical particles agglomerated from MgFe{sub 2}O{sub 4} nanocrystallites ∼9.6 and ∼11.5 nm in size function as cores coated with SiO{sub 2} shells ∼30 and ∼50 nm thick, respectively. The total size of obtained CS MNCs is ∼200 and 300 nm, respectively. Synthesized CS MgFe{sub 2}O{sub 4}/SiO{sub 2} MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

CHALLENGING SOME CONTEMPORARY VIEWS OF CORONAL MASS EJECTIONS. I. THE CASE FOR BLAST WAVES

Since the closure of the “solar flare myth” debate in the mid-1990s, a specific narrative of the nature of coronal mass ejections (CMEs) has been widely accepted by the solar physics community. This narrative describes structured magnetic flux ropes at the CME core that drive the surrounding field plasma away from the Sun. This narrative replaced the “traditional” view that CMEs were blast waves driven by solar flares. While the flux rope CME narrative is supported by a vast quantity of measurements made over five decades, it does not adequately describe every observation of what have been termed CME-related phenomena. In this paper we present evidence that some large-scale coronal eruptions, particularly those associated with EIT waves, exhibit characteristics that are more consistent with a blast wave originating from a localized region (such as a flare site) rather than a large-scale structure driven by an intrinsic flux rope. We present detailed examples of CMEs that are suspected blast waves and flux ropes, and show that of our small sample of 22 EIT-wave-related CMEs, 91% involve a blast wave as at least part of the eruption, and 50% are probably blast waves exclusively. We conclude with a description of possible signatures to look for in determining the difference between the two types of CMEs and with a discussion on modeling efforts to explore this possibility.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Magnetic Flux Cancellation as the Origin of Solar Quiet-region Pre-jet Minifilaments

We investigate the origin of 10 solar quiet-region pre-jet minifilaments , using EUV images from the Solar Dynamics Observatory ( SDO )/Atmospheric Imaging Assembly (AIA) and magnetograms from the SDO Helioseismic and Magnetic Imager (HMI). We recently found that quiet-region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancellation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancellation between minority-polarity and majority-polarity flux patches. In each of 10 pre-jet regions, we find that opposite-polarity patches of magnetic flux converge and cancel, with a flux reduction of 10%–40% from before to after the minifilament appears. For our 10 events, the minifilaments exist for periods ranging from 1.5 hr to 2 days before erupting to make a jet. Apparently, the flux cancellation builds a highly sheared field that runs above and traces the neutral line, and the cool transition region plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancellation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus, our observations strongly support that quiet-region magnetic flux cancellation results in both the formation of the pre-jet minifilament and its jet-driving eruption.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Future application of Czochralski crystal pulling for silicon

Czochralski (Cz) crystal pulling has been the predominant method used for preparing silicon single crystal for the past twenty years. The fundamental technology used has changed little. However, great strides have been made in learning how to make the crystals bigger and of better quality at ever increasing productivity rates. Currently charge sizes of 50 kg of polycrystal silicon are being used for production and crystals up to ten inches in diameter have been grown without major difficulty. The largest material actually being processed in silicon wafer form is 150 mm (6 inches) in diameter. Growing of crystals in a magnetic field has proved to be particularly useful for microscopic impurity control. Major developments in past years on equipment for Cz crystal pulling have included the automatic growth control of the diameter as well as the starting core of the crystal, the use of magnetic fields and around the crystal puller to supress convection, various recharging schemes for dopant control and the use of continuous liquid feed in the crystal puller. The latter, while far from being a reliable production process, is ideal in concept for major improvement in Cz crystal pulling. The Czochralski process will maintain its dominance of silicon crystal production for many years.

Matlcok, J. H.↗
DOE OSTI2021

Overview of the fusion nuclear science facility, a credible break-in step on the path to fusion energy

The Fusion Nuclear Science Facility (FNSF) is examined here as part of a two step program from ITER to commercial power plants. This first step is considered mandatory to establish the materials and component database in the real fusion in-service environment before proceeding to larger electricity producing facilities. The FNSF can be shown to make tremendous advances beyond ITER, toward a power plant, particularly in plasma duration and fusion nuclear environment. A moderate FNSF is studied in detail, which does not generate net electricity, but does reach the power plant blanket operating temperatures. The full poloidal Dual Coolant Lead Lithium (DCLL) blanket is chosen, with alternates being the Helium Cooled Lead Lithium (HCLL) and Helium Cooled Ceramic Breeder/Pebble Bed (HCCB/PB). Several power plant relevant choices are made in order to follow the philosophy of targeted technologies. Any fusion core component must be qualified by fusion relevant neutron testing and highly integrated non-nuclear testing before it can be installed on the FNSF in order to avoid the high probability of constant failures in a plasma-vacuum system. A range of missions for the FNSF, or any fusion nuclear facility on the path toward fusion power plants, are established and characterized by several metrics. A conservative physics strategy is pursued to accommodate the transition to ultra-long plasma pulses, and parameters are chosen to represent the power plant regime to the extent possible. An operating space is identified, and from this, one point is chosen for further detailed analysis, with R = 4.8 m, a = 1.2 m, IP = 7.9 MA, BT = 7.5 T, βN Gr = 0.9, fBS = 0.52, q95 = 6.0, H98 ∼1.0, and Q = 4.0. The operating space is shown to be robust to parameter variations. A program is established for the FNSF to show how the missions for the facility are met, with a He/H, a DD and 5 DT phases. The facility requires ∼25 years to complete its DT operation, including 7.8 years of neutron production, and the remaining spent on inspections and maintenance. The DD phase is critical to establish the ultra-long plasma pulse lengths. The blanket testing strategy is examined, and shows that many sectors have penetrations for heating and current drive (H/CD), diagnostics, or Test Blanket Modules (TBMs). The hot cell is a critical facility element in order for the FNSF to perform its function of developing the in-service material and component database. The pre-FNSF R&D is laid out in terms of priority topics, with the FNSF phases driving the time-lines for R&D completion. A series of detailed technical assessments of the FNSF operating point are reported in this issue, showing the credibility of such a step, and more detailed emphasis on R&D items to pursue. These include nuclear analysis, thermo-mechanics and thermal-hydraulics, liquid metal thermal hydraulics, transient thermo-mechanics, tritium analysis, maintenance assessment, magnet specification and analysis, materials assessments, core and scrape-off layer (SOL)/divertor plasma examinations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Overview of the fusion nuclear science facility, a credible break-in step on the path to fusion energy

Here the Fusion Nuclear Science Facility (FNSF) is examined as part of a two step program from ITER to commercial power plants. This first step is considered mandatory to establish the materials and component database in the real fusion in-service environment before proceeding to larger electricity producing facilities. The FNSF can be shown to make tremendous advances beyond ITER, toward a power plant, particularly in plasma duration and fusion nuclear environment. A moderate FNSF is studied in detail, which does not generate net electricity, but does reach the power plant blanket operating temperatures. The full poloidal Dual Coolant Lead Lithium (DCLL) blanket is chosen, with alternates being the Helium Cooled Lead Lithium (HCLL) and Helium Cooled Ceramic Breeder/Pebble Bed (HCCB/PB). Several power plant relevant choices are made in order to follow the philosophy of targeted technologies. Any fusion core component must be qualified by fusion relevant neutron testing and highly integrated non-nuclear testing before it can be installed on the FNSF in order to avoid the high probability of constant failures in a plasma-vacuum system. A range of missions for the FNSF, or any fusion nuclear facility on the path toward fusion power plants, are established and characterized by several metrics. A conservative physics strategy is pursued to accommodate the transition to ultra-long plasma pulses, and parameters are chosen to represent the power plant regime to the extent possible. An operating space is identified, and from this, one point is chosen for further detailed analysis, with R = 4.8 m, a = 1.2 m, I P = 7.9 MA, B T = 7.5 T, β N < 2.7, n/n Gr = 0.9, f BS = 0.52, q95 = 6.0, H 98 ~1.0, and Q = 4.0. The operating space is shown to be robust to parameter variations. A program is established for the FNSF to show how the missions for the facility are met, with a He/H, a DD and 5 DT phases. The facility requires ~25 years to complete its DT operation, including 7.8 years of neutron production, and the remaining spent on inspections and maintenance. The DD phase is critical to establish the ultra-long plasma pulse lengths. The blanket testing strategy is examined, and shows that many sectors have penetrations for heating and current drive (H/CD), diagnostics, or Test Blanket Modules (TBMs). The hot cell is a critical facility element in order for the FNSF to perform its function of developing the in-service material and component database. The pre-FNSF R&D is laid out in terms of priority topics, with the FNSF phases driving the time-lines for R&D completion. A series of detailed technical assessments of the FNSF operating point are reported in this issue, showing the credibility of such a step, and more detailed emphasis on R&D items to pursue. These include nuclear analysis, thermo-mechanics and thermal-hydraulics, liquid metal thermal hydraulics, transient thermo-mechanics, tritium analysis, maintenance assessment, magnet specification and analysis, materials assessments, core and scrape-off layer (SOL)/divertor plasma examinations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Exploring the structural and magnetic properties of TiO{sub 2}/SnO{sub 2} core/shell nanocomposite: An experimental and density functional study

TiO{sub 2}/SnO{sub 2} core/shell nanocomposite is prepared via a simple sol–gel method and the properties are compared with the individual TiO{sub 2} (core) and SnO{sub 2} (shell). The corresponding characterizations are carried out in terms of structural and magnetic properties of TiO{sub 2}/SnO{sub 2}, TiO{sub 2} and SnO{sub 2} nanosystems. Structural properties are studied via XRD, TEM, Raman spectroscopy, FTIR and XPS. Magnetic characterization is performed by measuring Moment vs. Applied Field for all the samples and Moment vs. Temperature for TiO{sub 2}/SnO{sub 2} core/shell nanocomposite. We also went for a better insight with the help of theoretical measures. First principle calculations have been executed using “Density Functional Theory” (DFT)-based MedeA VASP package to compare the results of TiO{sub 2}/SnO{sub 2} with TiO{sub 2} (1 1 0) and SnO{sub 2} (1 1 0) surface calculations and its effect on the magnetic nature of the specific nanoparticles. XRD, RAMAN and FTIR gave indirect evidence of formation of core shell nanostructure while TEM micrographs provide the direct evidence of formation of core shell nanostructure. The magnetic study shows a higher saturation magnetization for the core/shell nanostructure compared to pristine TiO{sub 2} and SnO{sub 2}. In this report, we have attempted to relate this experimental observation with the results of the first principle calculations. - Graphical abstract: Above pictorial presentation (from left) represents the model for TS, TiO{sub 2} and SnO{sub 2} used for DFT calculation and the obtained magnetic results for all the prepared systems. - Highlights: • Synthesis of TiO{sub 2}/SnO{sub 2} core/shell nanocomposites by a simple sol–gel technique. • The nanocomposites show better magnetic property than pristine nanoparticles. • DFT based calculations also support the experimental evidences.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Massive quiescent cores in Orion. V. The internal structures and physical and chemical properties of two extremely dense cores

We present a high-resolution (∼ 1.''5) observational study of two massive dust-gas cores, ORI8nw{sub 2} and ORI2{sub 6}, in the Orion molecular cloud using the Combined Array for Research in Millimeter-wave Astronomy. In each region the 3.2 mm continuum emission exhibits a dense and compact dust core at the center with 1-3 solar masses. The cores have number densities exceeding 10{sup 9} cm{sup –3}, which are among the highest volume densities observed in star-forming cores. In both regions the N{sub 2}H{sup +} shows clumpy structures that are spatially displaced from the densest gas. In OIR8nw{sub 2} in particular, the N{sub 2}H{sup +} shows a noticeable filament structure with a central cavity shell. The calculation for the dynamical state shows that this core can be potentially supported by the magnetic field against its gravitational instability, but the fragmentation might still occur and produce the observed N{sub 2}H{sup +} clumps if the gas density exceeds 5 × 10{sup 7} cm{sup –3} and this value is available within the observed density range. Also, the extremely high density at the core center suggests super-Jeans condition and the possibility for further fragmentation. For the chemical properties, the N{sub 2}H{sup +}-to-HCO{sup +} abundance ratios are shown to be different than those observed in infrared dark clouds. A combined analysis with the other Orion cores and the chemical model suggests that the different abundance ratios can be explained by the low CO abundances in our cores. To further reveal the evolution of such dense cores, higher resolution and sensitivity are required.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Deep sub-nanosecond reversal of vortex cores confined in a spin-wave potential well

A spin-wave potential well is created in a permalloy nanodisk by setting up a cylindrical cavity in the center of the sample. We then apply a single-harmonic external magnetic field perpendicular to the disk plane to switch the vortex polarity of the sample. Our micromagnetic numerical studies establish that the effective spin-wave confinement by the potential well leads to much stronger magnetization oscillation in the sample. Therefore, the vortex core can be reversed well below 200 ps and over a wide range of field frequency. Our findings present an additional efficient means for ultrafast switching of magnetic vortices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Achievements of actively controlled divertor detachment compatible with sustained high confinement core in DIII-D and EAST

The compatibility of efficient divertor detachment with high-performance core plasma is vital to the development of magnetically controlled fusion energy. The joint research on the EAST and DIII-D tokamaks demonstrates successful integration of divertor detachment with excellent core plasma confinement quality, a milestone towards solving the critical plasma–wall-interaction (PWI) issue and core-edge integration for ITER and future reactors. In EAST, actively controlled partial detachment with T et,div ~ 5 eV around the strike point and H 98 > 1 in different H-mode scenarios including the high β P H-mode scenario have been achieved with ITER-like tungsten divertor, by optimizing the detachment access condition and performing detailed experiments for core-edge integration. For active long-pulse detachment feedback control, a 30 s H-mode operation with detachment-control duration being 25 s has been successfully achieved in EAST. DIII-D has achieved actively controlled fully detached divertor with low plasma electron temperature (T et,div ≤ 5 eV across the entire divertor target) and low particle flux (degree of detachment, DoD > 3), simultaneously with very high core performance (β N ~3, β P > 2 and H 98 ~ 1.5) in the high βP scenario being developed for ITER and future reactors. The high-β P high confinement scenario is characterized by an internal transport barrier (ITB) at large radius and a weak edge transport barrier (ETB, or pedestal), which are synergistically self-organized. Both the high-β P scenario and impurity seeding facilitate divertor detachment. The detachment access leads to the reduction of ETB, which facilitates the development of an even stronger ITB at large radius in the high β P scenario. Thus, this strong large radius ITB enables the core confinement improvement during detachment. In conclusion, these significant joint DIII-D and EAST advances on the compatibility of high confinement core and detached divertor show a great potential for achieving a high-performance core plasma suitable for long-pulse operation of fusion reactors with controllable steady-state PWIs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Internal constitution of Mars.

Models of the internal structure of Mars consistent with the mass, radius and moment of inertia of the planet are constructed. The models assume that the radius of the core is between 0.36 and 0.60 of the radius of the planet, that the zero-pressure density of the mantle is between 3.54 and 3.49 g/cu cm, and that the planet contains 25 to 28% iron. Meteorite models of Mars containing 25 wt % iron and 12 wt % core are also proposed. It is maintained that Mars in contrast to the earth is an incompletely differentiated planet with a core substantially richer in sulfur than the core of the earth. The absence of a magnetic field on Mars is possibly linked with lack of lunar precessional torque and the small size and high resistivity of the Martian core.

Anderson, D. L.↗
DOE OSTI2026

Geostrophic to magnetically-damped turbulence in liquid metal rotating magnetoconvection

Understanding planetary core convection dynamics requires the study of convective flows in which the Coriolis and Lorentz forces attain a leading-order, so-called magnetostrophic balance. Experimental investigations of rotating magnetoconvection (RMC) in the magnetostrophic regime are therefore essential to broadly characterize the properties of local-scale planetary core flow. Toward this end, we present here the first thermovelocimetric measurements of magnetostrophic, liquid metal convection, which are made using liquid gallium as the working fluid, at moderate rotation rates (Ekman numbers 10 -4 ≤ Ek ≤ 10 -5 ) and in the presence of dynamically strong magnetic fields (Elsasser number Λ = 1). Complementary rotating convection (RC) experiments are performed at the same rotation rates to serve as reference cases. Our RMC velocity measurements adequately follow a geostrophic turbulent scaling for cases in which local-scale convective inertial forces exceed the Lorentz forces in the fluid bulk. In cases where Lorentz forces exceed local-scale inertia (local or convective interaction parameter N ℓ or N C ≳ 3), the root-mean-square RMC velocities are magnetically damped, yielding values below the geostrophic turbulent RC scaling prediction. An enhancement in heat transfer is observed, which we attribute to the increased coherence of vertically aligned magnetostrophic convective flow. Finally, our results and comparisons to dynamo simulations suggest that the system is in the strong-field regime, where convection-scale flows are magnetically damped with N C ≳ 3).

Convective turbulence↗
DOE OSTI2018

Design of a Modular E-Core Flux Concentrating Transverse Flux Machine

In this paper, a novel E-Core transverse flux machine (TFM) is proposed. The machine has a double stator-single rotor configuration with flux concentrating ferrite magnets and pole windings across each leg of an E-Core stator. E-Core stators with the proposed flux-concentrating rotor arrangement result in better magnet utilization and higher torque density. The machine also has a modular structure facilitating simpler construction. This paper presents a single phase and a two-phase version of the E-Core machine. Case study for a 1 kW, 400 r/min machine for both the single phase and two-phase TFM is presented.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Experimental constraints on the sound velocities of cementite Fe 3 C to core pressures

Sound velocities of cementite Fe 3 C have been measured up to 1.5 Mbar and at 300 K in a diamond anvil cell using the nuclear resonant inelastic X-ray scattering (NRIXS) technique. From the partial phonon density of states (pDOS) and equation of state (EOS) of Fe 3 C, we derived its elastic parameters including shear modulus, compressional (V-p) and shear-wave (V-s) velocities to core pressures. A pressure-induced spin-pairing transition in the powdered Fe3C sample was found to occur gradually between 10 and 50 GPa by the X-ray Emission Spectroscopy (XES) measurements. Following the completion of the spin-pairing transition, the V p and V s of low-spin Fe 3 C increased with pressure at a markedly lower rate than its high-spin counterpart. Our results suggest that the incorporation of carbon in solid iron to form iron carbide phases, Fe 3 C and Fe 7 C 3 , could effectively lower the V s but respectively raise the Poisson's ratio by 0.05 and 0.07 to approach the seismically observed values for the Earth's inner core. In conclusion, the comparison with the preliminary reference Earth model (PREM) implies that an inner core composition containing iron and its carbon-rich alloys can satisfactorily explain the observed seismic properties of the inner core.

58 GEOSCIENCES↗
DOE OSTI2024

Acoustic and electrical properties of Fe-Ti oxides with application to the deep lunar mantle

The overturn of titanium-rich mantle cumulates has been invoked to explain the structure and dynamics of the Moon. These dense cumulates are stable at the core-mantle boundary (CMB) and could explain field observations inferred from geophysical studies. Here, we report acoustic and electrical experiments on natural ilmenite-rutile aggregates up to 4.5 GPa and 1920 K. Seismic velocities show a weak pressure and temperature dependence, with Vs ~ 4.2 (+/-0.2) km/s and Vp ~8.0 (+/-0.2) km/s at the CMB conditions. Conductivity increases by a factor of 10 4 from 373 to 1920 K and is >10(3) S/m above 1573 K. Seismic and electrical models for the lunar mantle based on our results, considering mixtures of Fe-Ti oxides and olivine, indicate that field velocity and conductivity estimates are reproduced satisfactorily with 3-16 vol.% Fe-Ti oxides and 20 vol.% melt. Interactions between a Ti-rich, melt-bearing layer and the adjacent core likely affect the cooling and magnetic history of the Moon.

58 GEOSCIENCES↗