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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Spatial heterodyne spectroscopy for fast local magnetic field measurements of magnetized fusion plasmas

A novel spectroscopy diagnostic for measuring internal magnetic fields in high temperature magnetized plasmas has been developed. It involves spectrally resolving the Balmer- α (656 nm) neutral beam radiation split by the motional Stark effect with a spatial heterodyne spectrometer (SHS). The unique combination of high optical throughput (3.7 mm 2 sr) and spectral resolution (δλ ~ 0.1 nm) allows these measurements to be made with time resolution $\ll$1 ms. The high throughput is effectively utilized by incorporating a novel geometric Doppler broadening compensation technique in the spectrometer. The technique significantly reduces the spectral resolution penalty inherent to using large area, high-throughput optics while still collecting the large photon flux provided by such optics. In this work, fluxes of order 10 10 s –1 support the measurement of deviations of <5 mT (Δ λ Stark ~ 10 –4 nm) in the local magnetic field with 50 µs time resolution. Example high time resolution measurements of the pedestal magnetic field throughout the ELM cycle of a DIII-D tokamak plasma are presented. Local magnetic field measurements give access to the dynamics of the edge current density, which is essential to understanding stability limits, edge localized mode generation and suppression, and predicting performance of H-mode tokamaks.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Anisotropic magnetic and transport properties of orthorhombic o-Pr 2 Co 3 Ge 5

Abstract The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr 2 Co 3 Ge 5 (U 2 Co 3 Si 5 -type, Ibam ). Our findings show that o -Pr 2 Co 3 Ge 5 hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges near T sp = 32 K, with a spin reconfiguration transition near T M = 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity of T sp and T M . The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr 2 Co 3 Ge 5 is an environment for complex f state magnetism with potential strongly correlated electron states.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe 3

LaCrGe 3 has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. In this work, we combined thermodynamic (specific heat and thermal expansion), transport, x-ray, and neutron scattering as well as μSR measurements to obtain insights on the temperature-pressure phase diagram of LaCrGe 3 . Consistent with previous studies of the phase diagram by transport measurements, our thermodynamic data shows clearly that the FM transition at T FM changes its character from second order to first order when it is suppressed to low temperatures by pressure. In addition, previous studies demonstrated that for high pressures a new phase occurs below T 2 , which was proposed to be a long-wavelength antiferromagnetic state (AFM q ). In this paper, we provide evidence from our thermodynamic data that this phase transition is preceded by yet another phase transition at T 1 >T 2 . Our μSR data indicate that full magnetic volume fraction is only established below T 2 , but that this magnetism is characterized by a short correlation length. Within the experimental resolution, our neutron-scattering data is not able to identify any magnetic Bragg peaks. Overall, the microscopic magnetic data is therefore consistent with the formation of FM clusters in the proximity of the avoided FM quantum critical point in LaCrGe 3 . This conclusion is at odds with the previous proposal of AFM q order and raises questions on the role of disorder in this stochiometric compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Evidence for electronic signature of a magnetic transition in the topological magnet HoSbTe

Topological insulators with intrinsic magnetic order are emerging as an exciting platform to realize fundamentally new excitations from topological quantum states of matter. To study these systems and their physics, people have proposed a variety of magnetic topological insulator systems, including HoSbTe, an antiferromagnetic weak topological insulator candidate. Here, in this work, we use scanning tunneling microscopy to probe the electronic structure of HoSbTe with antiferromagnetic and ferromagnetic orders that are tuned by applying an external magnetic field. Although around the Fermi energy we find minor differences between the quasiparticle interferences under the ferromagnetic and antiferromagnetic orders, deep inside the valance region, a quasiparticle interference signal emerges with ferromagnetism. This observation is consistent with our first-principles calculations indicating the magnetism-driven transition of the electronic states in this spin-orbit coupled topological magnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Energetic Electron Transport in Magnetized Plasma with Magnetic Islands (Final Technical Report)

The main scientific goal of this project was to investigate the interactions between energetic electrons and magnetic islands in magnetized plasmas from lab to space. The proposed plan of addressed the following specific objectives: (1) Determine if energetic electrons are trapped by magnetic islands. Specifically, test the hypothesis that energetic electrons are trapped near island O-points due to stable orbits and de-confined near island X-points due to X-point tangles. (2) Determine how electron transport changes with island width and location. Specifically, test the hypothesis that electrons are accelerated by contracting magnetic islands through a Fermi acceleration process. (3) Assess how electron transport is affected by island dynamics, including island rotation, bifurcation, and/or island overlap. Specifically, test the hypothesis that electrons are deconfined and possibly accelerated during island rotations, bifurcations, and overlap due to stochastization of the magnetic field lines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Magnetic damping in ferromagnetic/heavy-metal systems: The role of interfaces and the relation to proximity-induced magnetism

Damping and spin transport in spintronic multilayered systems continues to be a topic of active research. The enhancement of damping in ferromagnet (FM)/spacer layer (SL)/heavy-metal (HM) thin-film systems was studied for Co 25 Fe 75 /SL/Pt with a nonmagnetic (NM) SL of either Au or Cu with variable thickness, in order to understand the correlation with proximity-induced magnetism (PIM) in the HM. Structural, PIM and magnetic damping measurements were undertaken on the same samples. Specifically, secondary ion mass spectroscopy, element specific x-ray magnetic reflectivity and x-ray magnetic circular dichroism at the Pt and Au L 3 edges, and ferromagnetic resonance methods were used. With increasing thickness of a Cu or Au SL directly between the FM and the Pt layer, the Pt PIM and the damping both fall rapidly, with a relationship between damping and PIM that depends on the SL material. The PIM observed in the Au layer showed a complex dependence on the layer thickness, suggesting some hybridization with the Pt. The role of the number and location of interfaces on the damping was demonstrated with the addition of a SL within the Pt layer, which showed that the specific details of the NM/HM interface also affects the damping. The insertion of a Cu SL within the Pt showed a measurable increase in the overall enhancement of the damping while the insertion of a Au SL into Pt had almost no effect on the damping. Finally, together these results demonstrate the role of both PIM and of additional interfaces in the enhancement of damping in FM/HM systems, which is not fully accounted for by existing theory

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetic and Mechanical Analysis of a Large Aperture 15 T Cable Test Facility Dipole Magnet

The US Department of Energy (DOE) Office of Science (SC), is funding a large bore “Cable Test Facility Magnet” for testing advanced cables and inserts in high transverse field. This is a joint effort between the Office of High Energy Physics (HEP) and the Office of Fusion Energy Sciences (FES). The background field magnet for this facility is being developed at Lawrence Berkeley National Laboratory (LBNL) while the cryostat and test facility will be located and operated by Fermi National Accelerator Laboratory (FNAL). The Nb 3 Sn dipole magnet, which will provide the transverse background field, is designed to generate a field of 15 T in a 100 × 150 mm bore at 1.9 K. The conceptual design of a block-type dipole with flared ends and a structure based on key-and-bladder technology will be introduced. The results of the magnetic and mechanical analysis will be presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

High‐Efficiency Magnon‐Mediated Magnetization Switching in All‐Oxide Heterostructures with Perpendicular Magnetic Anisotropy

Abstract The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron‐mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all‐oxide heterostructures of SrRuO 3 /NiO/SrIrO 3 are epitaxially grown on SrTiO 3 single‐crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO 3 with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO 3 with strong spin–orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion‐related energy dissipation from electron‐mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all‐oxide spintronic devices operated by magnon current.

Zheng, Dongxing↗
DOE OSTI2020

Magnetic well and Mercier stability of stellarators near the magnetic axis

We have recently demonstrated that by expanding in small distance from the magnetic axis compared with the major radius, stellarator shapes with low neoclassical transport can be generated efficiently. To extend the utility of this new design approach, here we evaluate measures of magnetohydrodynamic interchange stability within the same expansion. In particular, we evaluate the magnetic well, Mercier's criterion, and resistive interchange stability near a magnetic axis of arbitrary shape. In contrast to previous work on interchange stability near the magnetic axis, which used an expansion of the flux coordinates, here we use the ‘inverse expansion’ in which the flux coordinates are the independent variables. Reduced expressions are presented for the magnetic well and stability criterion in the case of quasisymmetry. The analytic results are shown to agree with calculations from the VMEC equilibrium code. Finally, we show that near the axis, Glasser, Greene and Johnson's stability criterion for resistive modes approximately coincides with Mercier's ideal condition.

Physics↗
DOE OSTI2022

A topological kagome magnet in high entropy form

AbstractTopological kagome magnets RMn 6 Sn 6 (R = rare earth element) attract numerous interests due to their non-trivial band topology and room-temperature magnetism. Here, we report a high entropy version of kagome magnet, (Gd 0.38 Tb 0.27 Dy 0.20 Ho 0.15 )Mn 6 Sn 6 . Such a high entropy material exhibits multiple spin reorientation transitions, which is not seen in all the related parent compounds and can be understood in terms of competing magnetic interactions enabled by high entropy. Furthermore, we also observed an intrinsic anomalous Hall effect, indicating that the high entropy phase preserves the non-trivial band topology. These results suggest that high entropy may provide a route to engineer the magnetic structure and expand the horizon of topological materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Exchange-biased quantum tunnelling of magnetization in a [Mn 3 ] 2 dimer of single-molecule magnets with rare ferromagnetic inter-Mn 3 coupling

A covalently-linked dimer of two single-molecule magnets (SMMs), [Mn 6 O(O 2 CMe) 6 (1,3-ppmd) 3 ](ClO 4 ) 2 , has been synthesized from the reaction of [Mn 3 O(O 2 CMe) 6 (py) 3 ](ClO 4 ) with 1,3-phenylene-bis(pyridin-2-ylmethanone) dioxime (1,3-ppmdH 2 ). It contains two [Mn III 3 O] +7 triangular units linked by three 1,3-ppmd 2 - groups into an [Mn 3 ] 2 dimer with D 3 symmetry. Solid-state dc and ac magnetic susceptibility measurements showed that each Mn 3 subunit retains its properties as an SMM with an S = 6 ground state. Magnetization vs. dc field sweeps on a single crystal reveal hysteresis loops below 1.3 K exhibiting exchange-biased quantum tunnelling of magnetization (QTM) steps with a bias field of +0.06 T. This is the first example of a dimer of SMMs showing a positive exchange bias of the QTM steps in the hysteresis loops, and it has therefore been subjected to a detailed analysis. Simulation of the loops determines that each Mn3 unit is exchange-coupled with its neighbour primarily through the 1,3-ppmd 2 - linkers, confirming a weak ferromagnetic inter-Mn 3 interaction of J 12 ≈ +6.5 mK ($\hat{H}= -2J\hat{S}_i·\hat{S}_j$ convention). High-frequency EPR studies of a microcrystalline powder sample enable accurate determination of the zero-field splitting parameters of the uncoupled Mn3 SMMs, while also confirming the weak exchange interaction between the two SMMs within each [Mn 3 ] 2 dimer. The combined results emphasize the ability of designed covalent linkers to generate inter-SMM coupling of a particular sign and relative magnitude, and thus the ability of such linkers to modulate the quantum physics. As such, this article supports the feasibility of using designed covalent linkers to develop molecular oligomers of SMMs, or other magnetic molecules, as multi-qubit systems and/or other components of new quantum technologies.

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

Spin dynamics and relaxation in 7.6 nm thin film of La 0.7 Sr 0.3 MnO 3 /SrTiO 3 : ac magnetic susceptibility and magnetic viscosity investigations

Analysis of the results from our investigations of the temperature dependence of ac susceptibilities (χ' and χ'') and magnetic viscosity in a 7.6 nm thin film of La 0.7 Sr 0.3 MnO 3 grown on SrTiO 3 (001) substrate is presented. The Curie temperature (T C ) of this film is magnetic field (H) dependent, varying as [T C (H) - T C (0)] ~ H n with T C (0) = 270 K and n = 0.15. Temperature dependence of χ' and χ'' measured at ac frequencies f m in the range of 0.1–10 kHz shows a broad peak near 230 K associated with the blocking temperature (T B ) of spin clusters present in the 1.4 nm surface layer and a frequency dependent peak near 270 K associated with T C . The mean relaxation time τ determined from the Cole–Cole analysis of the temperature dependent χ' and χ'' is shown to fit the Vogel–Fulcher law: τ = τ 0 exp[ΔE/k B (T - T 0 )] with T 0 = 245 K, ΔE/k B = 270 K = T C and τ 0 = 1.2 x 10 -9 s. Magnetic viscosity S (measured in H = 0 for a sample cooled in H = 50 Oe) determined from the fit to the magnetization: M (t)= M (0) – S ln t, with time t up to 2 h, shows a peak at 230 K above which M (2 h) switches to negative values for temperatures up to T C (0). It is argued that this negative magnetization results from an interaction between the superparamagnetic spin clusters and the ferromagnetic phase, both being present in the temperature range of T B < T < T C .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Generation of strong magnetic fields for magnetized plasma experiments at the 1-MA pulsed power machine

Pulsed power technology provides a platform for investigating plasmas in strong magnetic fields using a university-scale machine. Presented here are methods for generating and measuring the 1–4-MG magnetic fields developed for the 1-MA Zebra pulsed power generator at the University of Nevada, Reno. A laser coupled with the Zebra generator produces a magnetized plasma, and experiments investigate how a megagauss magnetic field affects the two-plasmon decay and the expansion of the laser-produced plasma in both transverse and longitudinal magnetic fields.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

A kinetic model of friction in strongly coupled strongly magnetized plasmas

Plasmas that are strongly magnetized in the sense that the gyrofrequency exceeds the plasma frequency exhibit novel transport properties that are not well understood. As a representative example, we compute the friction force acting on a massive test charge moving through a strongly coupled and strongly magnetized one-component plasma using a generalized Boltzmann kinetic theory. Recent works studying the weakly coupled regime have shown that strong magnetization leads to a transverse component of the friction force that is perpendicular to both the Lorentz force and velocity of the test charge, in addition to the stopping power component aligned antiparallel to the velocity. Recent molecular dynamics simulations have also shown that strong Coulomb coupling in addition to strong magnetization gives rise to a third component of the friction force in the direction of the Lorentz force. Here, we show that the generalized Boltzmann kinetic theory captures these effects and generally agrees well with the molecular dynamics simulations over a broad range of Coulomb coupling and magnetization strength regimes. The theory is also used to show that the “gyro” component of the friction in the direction of the Lorentz force arises due to asymmetries associated with gyromotion during short-range collisions. Computing the average motion of the test charge through the background plasma, the transverse force is found to strongly influence the trajectory by changing the gyroradius and the gyrofriction force is found to slightly change the gyrofrequency of the test charge resulting in a phase shift.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Confinement of relativistic electrons in a magnetic mirror en route to a magnetized relativistic pair plasma

Creating a magnetized relativistic pair plasma in the laboratory would enable the exploration of unique plasma physics relevant to some of the most energetic events in the universe. As a step toward a laboratory pair plasma, we have demonstrated an effective confinement of multi-MeV electrons inside a pulsed-power-driven 13 T magnetic mirror field with a mirror ratio of 2.6. The confinement is diagnosed by measuring the axial and radial losses with magnetic spectrometers. The loss spectra are consistent with ≤2.5 MeV electrons confined in the mirror for ∼1 ns. With a source of 1012 electron-positron pairs at comparable energies, this magnetic mirror would confine a relativistic pair plasma with Lorentz factor γ∼6 and magnetization σ∼40.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Controlling the size of non-axisymmetric magnetic footprints using resonant magnetic perturbations

The structure of the non-axisymmetric heat load distribution at the divertor plates is determined not only by the toroidal but also from the poloidal spectrum of non-axisymmetric field perturbations. Whether they are intrinsic, like error fields, or they are applied through 3D coils, the non-axisymmetric fields produce complex 3D edge magnetic topologies (footprints) that alter the properties of the heat and particle flux distributions on the divertor target plates. In this manuscript, a study of the impact of applied 3D field poloidal spectrum on the footprint size and structure is done for the DIII-D tokamak using the resistive MHD code M3D-C1 coupled with the field line tracing code TRIP3D. To resolve the impact of the poloidal spectrum of the magnetic perturbation, the relative phase of the two rows of in-vessel 3D coils used to produce both a n = 2 and a n = 3 perturbation is varied, where n is the toroidal harmonic of the magnetic perturbation. This shows that the largest footprint is predicted when the relative phase of the two rows is close to zero, which is also where the resonant coupling with the plasma is maximized. These results suggest that it will be challenging to decouple the footprint size from the requisite resonant coupling for RMP–ELM control. The correlation between the measured heat load and particle flux distributions at the outer divertor plates in DIII-D and the magnetic measurements is in good agreement with the predicted dependence of the magnetic footprint size on the amplitude of the resonant component of the plasma response.

3D fields↗
DOE OSTI2025

Precise magnetic field mapping of the EMPHATIC Phase 1 magnet with COMSOL

A compact Halbach array magnet is used to measure the momentum of the secondary particles in EMPHATIC(Experiment to Measure the Production ofHadrons At a Test beam InChicagoland). Hall probe data was taken for the central cylindrical bore of the magnet and a field map was constructed. COMSOL Multiphysics® Software is used for modeling the magnet and constructing the corresponding magnetic field map. Here, we present a fitting approach where the hall probe data is used to determine a 1mm-spacing map of the entire volume of the magnet using COMSOL. The new map will allow for linear interpolation within the volume, and expand the map to outside the measurement volume, thus increasing the acceptance and precision of EMPHATIC's tracking system.

47 OTHER INSTRUMENTATION↗