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DOE OSTI2021

Strongly heat-assisted spin–orbit torque switching of a ferrimagnetic insulator

Ferrimagnetic insulators promise low-power and high-speed spintronic applications, thanks to their insulating nature and fast dynamics near compensation points. In a ferrimagnetic insulator/heavy metal heterostructure, we investigate field- and current-induced magnetization switching at various temperatures and observe distinct magnetization switching behaviors owing to spin-orbit torque (SOT) and heating effect. We have realized SOT switching across the magnetization compensation temperature and discovered that the SOT switching is strongly heat-assisted: the temperature is always above the compensation temperature while the SOT switching happens in our case. Moreover, we show that the SOT efficiency is strongly magnetization-dependent by characterizing the current dependence of SOT efficiency and explaining the anomalous SOT switching back phenomena in the presence of a titled external field. Our results reveal the critical role of Joule heating on the dynamics of magnetic insulators and pave the way for the application of spintronic devices based on magnetic insulators.

36 MATERIALS SCIENCE↗

NASA NTRSDate not supplied

Development of a Cold-Walled Molten Regolith Electrolysis Reactor for Lunar Oxygen Production

On the lunar surface, production of commodi-ties to support human presence, such as water, food and oxygen, and sustain the growth of a per-manent outpostwill likely require the use oflocal resources. The moon is covered almost entirely withfragmented oxide minerals known as regolithhundreds of meter thick.As a resource, it is rich in oxygen (> 42 wt.%) bound in a solid state with a variety of metals. The molten regolith electrolysis (MRE)reactor is a promising technology for the production of gaseous oxygen from the lunar reg-olithin a simple, single-stepreaction that requires minimalconsumable materials, produces oxygen and metals with high electrical efficiency and high yields from any regolithcomposition.This process involvesmelting regolith to~1600°C then electro-lyzing the molten pool to separate metal and oxy-gen ions that are then collected as liquid metal and gaseous oxygen at the respective electrodes. Lab-scale demonstrations of the MRE technology have previously reliedon external heating sources to bring the entirety of the reactor up to the operating temperaturewhich creates corrosive interfaces be-tween the molten regolith and the containment ma-terial in the reactor, limiting the overall lifespan of a reactor[1]. The Gaseous Lunar Oxygen from Regolith Electrolysis (GaLORE) project is focused on the development of a “cold-walled” or “Joule-heated” reactor design in which an internal heating source is used to selectively melt a pool of regolith between the electrodes of the reactor, leaving a shell of solidified regolith between the molten pool and the containment vessel of the reactor. This next generation reactor concept has been under development as molten oxide electrolysis (MOE) by MIT and Boston Metal for the production of iron from pure ores for terrestrial application [2]. The GaLORE project in engaged in early development of the technology for use with varying lunar regolith compositionsin the lunar environment. Thermal modelling of a proposed cold-walledreac-tor design were used as a scaffold to develop pa-rameters for a feasible reactor shape and size as well as target energy consumption[3]. The current development effort for the cold-walled reactor de-sign will be presented as a trade study of the most promising techniques for melting regolithwithin the constraints imposed by the lunar environment.Heater devices are designed to accommodate lim-ited electrical power availabilityon the moon, a wide range of regolith compositions that may be seen on the moon, limited metals available for re-placing consumed parts,and the low thermal con-ductivity of granular regolith in vacuum.Heater de-vices will be down-selectedbased on performance measurements within the above operationalcon-straints,and selected devices will be integrated into a reactor with electrodes to begin producing oxygen. [1]Sibille,L.,Sadoway, D.R.,Sirk, A., Tripathy,P.,Melendez, O., Standish, E., Dominguez, J. A., Stefanescu, D.M.,Curreri, P.A., Poizeau,S.,2009. “Recent Advancesin Scale-up Development of Molten Regolith Electrolysis for Oxygen Production in support of a Lunar Base.”AIAA 2009-659, 47th AIAA Aerospace Sciences Meeting, 5 -8 January 2009, Orlando, FL. [2] Boston Metal, https://www.boston-metal.com/moe-technology/#moe-process[3]Schreiner, S.S.,Sibille, L., Dominguez, J.A., Hoffman, J.A., 2016. "A parametric sizing model for Molten Regolith Electrolysis reactors to pro-duce oxygen on the Moon." Advances in Space Research 57.,7,1585-1603.

K D Grossman↗

NASA NTRS2007

Mesospheric Dynamical Changes Induced by the Solar Proton Events in October-November 2003

The very large solar storms in October-November 2003 caused solar proton events (SPEs) at the Earth that impacted the upper atmospheric polar cap regions. The Thermosphere Ionosphere Mesosphere Electrodynamic General Circulation Model (TIME-GCM) was used to study the atmospheric dynamical influence of the solar protons that occurred in Oct-Nov 2003, the fourth largest period of SPEs measured in the past 40 years. The highly energetic solar protons caused ionization, as well as dissociation processes, and ultimately produced odd hydrogen (HOx) and odd nitrogen (NOy). Significant short-lived ozone decreases (10-70%) followed these enhancements of HOx and NOy and led to a cooling of most of the lower mesosphere. This cooling caused an atmospheric circulation change that led to adiabatic heating of the upper mesosphere. Temperature changes up to plus or minus 2.6 K were computed as well as wind (zonal, meridional, vertical) perturbations up to 20-25% of the background winds as a result of 22 the solar protons. The solar proton-induced mesospheric temperature and wind perturbations diminished over a period of 4-6 weeks after the SPEs. The Joule heating in the mesosphere, induced by the solar protons, was computed to be relatively insignificant for these solar storms with most of the temperature and circulation perturbations caused by ozone depletion in the sunlit hemisphere.

Jackman, Charles H.↗

DOE OSTI2022

Conversion degree and heat transfer in the cold cap and their effect on glass production rate in an electric melter

A predictive model of melt rate in waste glass vitrification operations is needed to inform melter operations during normal and off-normal operations. This paper describes the development of a model of the cold cap (the reacting melter feed floating on molten glass in a glass melter) that couples heat transfer with the feed-to-glass conversion kinetics. The model was applied to four melter feeds designed for high-level and low-activity nuclear waste feeds using the material properties, either measured or estimated, to obtain temperature and conversion distribution within the cold cap. The cold cap model, when coupled with a computational fluid dynamics model of a Joule-heated glass melter, allows the prediction of the glass production rate and power consumption. The results show reasonable agreement with the melting rates measured during pilot-scale melter tests.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS1995

Modeling of nonequilibrium space plasma flows

Godunov-type numerical solution of the 20 moment plasma transport equations. One of the centerpieces of our proposal was the development of a higher order Godunov-type numerical scheme to solve the gyration dominated 20 moment transport equations. In the first step we explored some fundamental analytic properties of the 20 moment transport equations for a low b plasma, including the eigenvectors and eigenvalues of propagating disturbances. The eigenvalues correspond to wave speeds, while the eigenvectors characterize the transported physical quantities. In this paper we also explored the physically meaningful parameter range of the normalized heat flow components. In the second step a new Godunov scheme type numerical method was developed to solve the coupled set of 20 moment transport equations for a quasineutral single-ion plasma. The numerical method and the first results were presented at several national and international meetings and a paper describing the method has been published in the Journal of Computational Physics. To our knowledge this is the first numerical method which is capable of producing stable time-dependent solutions to the full 20 (or 16) moment set of transport equations, including the full heat flow equation. Previous attempts resulted in unstable (oscillating) solutions of the heat flow equations. Our group invested over two man-years into the development and implementation of the new method. The present model solves the 20 moment transport equations for an ion species and thermal electrons in 8 domain extending from a collision dominated to a collisionless region (200 km to 12,000 km). This model has been applied to study O+ acceleration due to Joule heating in the lower ionosphere.

Gombosi, Tamas↗

NASA NTRS1984

Ion-neutral coupling in the high-latitude F region Evaluation of ion heating terms from Dynamics Explorer 2

Ion and neutral motions in the high latitude F layer were studied simultaneously during six passes of the Dynamics Explorer 2 spacecraft. The passes were made over the south polar cap in October 1981. An ion energy balance equation was defined to express the exchange of energy between the F layer and other atmospheric constituents. A momentum equation expressed the momentum exchange between the species. An approximate form of the energy balance equation was also formulated. The time constant for ion-neutral collisional momentum transfer significantly affected Joule heating in the F layer. Regions of large velocity disparities and ion temperature enhancements were detected as hot spots. The results indicate that a feedback mechanism may arise in terms of neutral compositional changes and enhanced ionospheric recombination. The approximate equation furnished values for ion heating rates which matched the data.

Killeen, T. L.↗

DOE OSTI2024

High-Fidelity Arc-Discharge Model for Hydrogen-Plasma-Smelting-Reduction of Iron Ore

Electrification and use of renewable hydrogen is currently a necessity for decarbonizing the iron-and-steel industry. In this regard, hydrogen plasma smelting reduction (HPSR) is a novel pathway that is being explored for reduction of iron ore. HPSR provides several decarbonization merits compared to conventional blast furnaces. Firstly, the use of renewable hydrogen drastically reduces the CO2 emissions compared to the use of coke. Secondly, renewable electricity in the form of a thermal plasma for making reactive hydrogen species (radicals, ions) are more efficient at reducing iron ore compared to neutral H2. Thirdly, a molten product compatible with downstream processes is obtained from the intense heat transfer from the plasma. However, the scale-up of this technology requires fundamental exploration of hydrogen plasma dynamics and its interaction with complex solid material that include phase changing iron-ore and slag. In this work, we present a first principles continuum scale model for thermal plasmas in Ar/H2 gas mixtures typically used for HPSR. The thermal plasma governing equations for mass, momentum and energy with Lorentz force and Joule heating source terms are solved along with electromagnetic equations for electrostatic and magnetic vector potential. Our solver will be based on Pele, a suite of reacting flow solvers designed for advanced scientific computing architectures (Henry De Frahan et al., Proceedings of SIAM Parallel Processing, 13-25, 2024), and will utilize adaptive mesh generation for enhanced resolutions at locations of intense physicochemical interactions. This study will present the impact of Ar to H2 ratios on excited/dissociated hydrogen species concentrations, plasma temperature and conductivity along with the impact of outgassed species (water, metal vapor, O, OH radicals) from ore surface on gas phase chemistry. Furthermore, the heat and species flux to the surface will be quantified as a function of applied voltages in a transferred arc configuration.

hydrogen plasma↗

NASA NTRS1989

Soft X-ray, microwave, and hard X-ray emission from a solar flare - Implications for electron heating and acceleration in current channels

The soft X-ray, microwave, and hard X-ray emissions from the solar flare of May 14, 1980 are studied. The flare consists of a gradual component in soft X-rays and microwaves and a superposed impulsive burst accompanied by hard X-ray emission. The impulsive phase of the flare appears in the soft X-ray emission as a temperature spike and as an increased rate of energy dissipation into the plasma. A new, spatially and spectrally distinct, microwave component appears during the impulsive burst. The data are interpreted in terms of Joule heating and the electric field acceleration of electrons in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft X-ray emitting plasma can be heated by a single current sheet only if the resistivity in the sheet is well above the classical, collisional resistivity. Conditions are also given for the hard X-ray emission to be from nonthermal electrons with classical resistivity.

Holman, Gordon D.↗

DOE OSTI2020

Fast-current-heating devices to study in situ phase formation in metallic glasses by using high-energy synchrotron radiation

Details of fast-resistive-heating setups, controlled heating ranging from ~10 1 K s –1 to ~10 3 K s –1 , to study in situ phase transformations (on heating and on cooling) in metallic glasses by high-energy synchrotron x-ray diffraction are discussed here. Both setups were designed and custom built at the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and have been implemented at the P02.1 Powder Diffraction and Total Scattering Beamline and the P21.1 Swedish Materials Science Beamline at PETRA III storage ring, DESY, Hamburg. The devices are interchangeable at both beamlines. Joule heating is triggered automatically and is timed with the incident beam and detector. The crystallization process can be controlled via a feedback circuit by monitoring the change in the time-dependent resistivity and temperature of glasses. Different ambient atmospheres, such as vacuum and inert gases (He and Ar), can be used to control oxidation and cooling. The main focus of these devices is on understanding the crystallization mechanism and kinetics in metallic glasses, which are brittle and for which fast heating gives defined glass–crystal composites with enhanced plasticity. As an example, phase-transformation sequence(s) in a prototyped Cu–Zr-based metallic glass is described on heating, and a crystalline phase beneficial to the plasticity is identified.

47 OTHER INSTRUMENTATION↗

NASA NTRS1981

Solar EUV energy budget of the thermosphere

The considered study represents an extension of investigations reported by Torr et al. (1980). The earlier investigations are concerned with a quantification of thermospheric UV energy partitions for steady state conditions. The heating efficiency was determined as a function of altitude for selected conditions. Its value was found to vary dynamically as a function of altitude, season, latitude, and solar cycle. The steady state solution reported earlier is extended in the current study to a time dependent solution over a diurnal cycle. It is pointed out that the reported results will make necessary a significant revision of thermospheric models. Thus, estimates of additional sources such as Joule heating obtained from global thermospheric circulation models will require reevaluation.

Torr, M. R.↗

DOE OSTI2020

On Hydrodynamics Generated from Electrostatic Discharges: A Heat Source Perspective

A parameter space map of a heat source depositing energy into a cylindrical spark channel modeling the hydrodynamic effects of an electrostatic discharge event is explored. The four parameters of spatial weight, λ R , rise time, τ r , fall time, τ f , and energy per unit length deposited in to the system, E 0 /h, were varied to observe resulting hydrodynamic phenomena. The energy budget con-sequences of the associated hydrodynamic flow are discussed in terms of the remaining electrical energy available for the joule heating of sensitive energetic materials (or “victims”) are discussed,where hydrodynamic simulations are validated by experimental data. Future results and conclusions will be added to this report as they are produced.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2020

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches 9.0 g cm − 3 , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1983

Nonthermal components of low energy electrons in the ionospheric E and F region

Rocket-borne instrument observations of very low energy electrons' energy distribution in the ionospheric E and F regions showed the regions to exist where an enhanced, high energy tail of thermal electrons appeared. One such appearance was amid a region of high electron temperature, T(e),associated with the Sq anomaly, where there were large T(e) deviations from the neutral temperature. The associated electron heating was most intense at 107 km, gradually decreasing toward 130 km, where both the T(e) and the excess high energy tail became small. In the second region, excess electrons appeared in the high energy tail at 135 km, reached an intensity peak at 150 km, and gradually decreased toward 210 km. It is suggested that the anomalously elevated T(e) and the enhanced energy tail in the first region were locally generated by some dynamo current-related mechanism distinct from Joule heating. The second region's high energy tail is also related to ionospheric currents.

Oyama, K. I.↗

NASA NTRS2010

Magnesium Diboride Current Leads

A recently discovered superconductor, magnesium diboride (MgB2), can be used to fabricate conducting leads used in cryogenic applications. Dis covered to be superconducting in 2001, MgB2 has the advantage of remaining superconducting at higher temperatures than the previously used material, NbTi. The purpose of these leads is to provide 2 A of electricity to motors located in a 1.3 K environment. The providing environment is a relatively warm 17 K. Requirements for these leads are to survive temperature fluctuations in the 5 K and 11 K heat sinks, and not conduct excessive heat into the 1.3 K environment. Test data showed that each lead in the assembly could conduct 5 A at 4 K, which, when scaled to 17 K, still provided more than the required 2 A. The lead assembly consists of 12 steelclad MgB2 wires, a tensioned Kevlar support, a thermal heat sink interface at 4 K, and base plates. The wires are soldered to heavy copper leads at the 17 K end, and to thin copper-clad NbTi leads at the 1.3 K end. The leads were designed, fabricated, and tested at the Forschungszentrum Karlsruhe - Institut foer Technische Physik before inclusion in Goddard's XRS (X-Ray Spectrometer) instrument onboard the Astro-E2 spacecraft. A key factor is that MgB2 remains superconducting up to 30 K, which means that it does not introduce joule heating as a resistive wire would. Because the required temperature ranges are 1.3-17 K, this provides a large margin of safety. Previous designs lost superconductivity at around 8 K. The disadvantage to MgB2 is that it is a brittle ceramic, and making thin wires from it is challenging. The solution was to encase the leads in thin steel tubes for strength. Previous designs were so brittle as to risk instrument survival. MgB2 leads can be used in any cryogenic application where small currents need to be conducted at below 30 K. Because previous designs would superconduct only at up to 8 K, this new design would be ideal for the 8-30 K range.

Panek, John↗

NASA NTRSDate not supplied

Connecting Uranus’ Magnetosphere and Upper Atmosphere via Electron Precipitation

Abstract. The precipitation of electrons is a key process through which significant energy is transferred from Uranus’ magnetosphere to its upper atmosphere. These electrons drive atmospheric ionization, thermospheric heating, and auroral emission at Uranus, and their properties are critical to address Uranus’ energy crisis as well as auroral phenomena. We combine measurements of auroral precipitation at Earth, Saturn, and Jupiter, with relevant Voyager 2 observations to estimate the properties of precipitating electrons at Uranus. In order to produce the measured aurora, energy fluxes of ~0.1mW/m 2 are required with energies of ~5keV.The acceleration of particles between the magnetosphere and thermosphere is predicted to be Earth-like, but with significantly lower overall energy flux and field aligned currents due to Uranus’ sparser magnetosphere. The height-integrated Joule heating rates of ~0.2 mW/m 2 are an order of magnitude lower than Earth

Daniel Gershman↗

DOE OSTI2025

Numerical investigation of magneto-inertial fusion targets magnetized by dynamic enforcement of helical current flow

Magnetized Liner Inertial Fusion (MagLIF) targets require premagnetization to reduce thermal conduction losses from the laser-heated fuel to the liner material during implosion. MagLIF targets are typically magnetized by external magnetic field coils which are technologically limited to providing <20 T axial magnetic fields in the fusion fuel. We present a novel target design, AutoMag-D, which employs dynamic enforcement of helical current in the liner, resulting in >20 T axial magnetic field in the fuel region prior to implosion without the need of external magnetic field coils. These self-magnetizing liners are made of helically oriented alternating electrically conductive material and electrically insulating material surrounded by a thin, conductive outer radial layer. As the liner is pulsed with a ∼ 20 MA, ∼ 100 ns rise time drive current from Z, the outer layer of conductive material is shocked and intensely Joule heated, causing it to melt, vaporize, and turn to plasma. This allows the magnetic drive field to diffuse radially inward which dynamically enforces current flow in the helical conduction paths in the liner and produces axial magnetic field in the fuel region prior to implosion of the inner liner surface. AutoMag-D liner designs do not require dielectric breakdown of electrically insulating material (as in traditional auto-magnetizing helical liners) and do not require helical return current geometries (as in dynamic screw pinches). We present results from three-dimensional radiation-magnetohydrodynamic simulations of MagLIF implosions employing AutoMag-D liner designs. Simulated AutoMag-D targets demonstrate improved fuel conditions and thermonuclear yield compared to traditional MagLIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

In Situ Study of Resistive Switching in a Nitride‐Based Memristive Device

Abstract Resistive switching (RS) devices with ultra‐low‐voltage threshold and reliable switching repeatability exhibits great potential applications in energy‐efficient data storage and neuromorphic computing. Understanding switching mechanisms at nanoscale is critical to design RS devices with improved performance. In this work, a lamella memristive device using focused ion beam (FIB) method based on the metal/TiO x /TiN/Si structure device is fabricated. In situ transmission electron microscopy (TEM) and current–voltage ( I–V ) characteristic demonstrate that the lamella device shows a volatile RS behavior with a threshold switching at ≈ ± 0.4 V. In situ scanning transmission electron microscopy (STEM) experiments with electron energy loss spectroscopy (EELS) reveal that the charge carriers such as oxygen vacancies migrate under positive/negative DC bias and modulate Schottky barriers at the top and bottom metal/semiconductor interfaces. The RS mechanism of the lamella device is based on the Schottky barriers modulation and Joule heating assisted electric field triggered thermal runaway (FTTR) occurred at the metal/semiconductor interfaces. The fundamental insights gained from this study presents a perspective on interface‐type RS devices processing and opens up new technological opportunities of fabricating ultra‐low‐energy memristive devices.

36 MATERIALS SCIENCE↗

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↗