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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Improvement of persistent magnetic field trapping in bulk Y-Ba-Cu-O superconductors

For type-II superconductors, magnetic field can be trapped due to persistent internal supercurrent. Quasi-persistent magnetic fields near 2 T at 60 K (and 1.4 T at 77 K) have been measured in minimagnets made of proton-irradiated melt-textured Y-Ba-Cu-O (MT-Y123) samples. Using the trapping effect, high-field permanent magnets with dipole, quadrupole, or more complicated configurations can be made of existing MT-Y123 material, thus bypassing the need for high-temperature superconductor (HTS) wires. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. This model is also a guide to select directions of materials development to further improve field trapping properties. General properties such as magnetic field intensities, spatial distributions, stabilities, and temperature dependence of trapped field are discussed.

Chen, In-Gann↗
NASA NTRS1998

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (less than 250 V) 4H-SiC p(+)n Junction diodes: DC Properties - Part 1

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = 1c with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4)/sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1998

Breakdown Degradation Associated with Elementary Screw Dislocations in 4H-SiC P(+)N Junction Rectifiers

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector greater than 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per sq cm, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p(+)n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p(+)n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

Neudeck, P. G.↗
NASA NTRS1999

Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices (Invited)

As illustrated by the invited paper at this conference and other works, SiC wafers and epilayers contain a variety of crystallographic imperfections, including micropipes, closed-core screw dislocations, grain boundaries, basal plane dislocations, heteropolytypic inclusions, and surfaces that are often damaged and contain atomically rough features like step bunching and growth pits or hillocks. Present understanding of the operational impact of various crystal imperfections on SiC electrical devices is reviewed, with an emphasis placed on high-field SiC power devices and circuits.

Neudeck, Philip G.↗
NASA NTRS1999

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (<250 V) 4H-SiC p+n Junction Diodes - Part 1: DC Properties

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = lc with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4) sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1999

The LISA Mission Design

The proposed Laser Interferometer Space Antenna (LISA) is designed to observe gravitational radiation from galactic binaries and massive black holes in other galaxies. LISA will observe waves in the frequency range 0.1 mHz to 1 Hz, which can never be observed on Earth due to background noise. The three LISA spacecraft will be located at the vertices of an equilateral triangle with side length 5 million km. The orbits are chosen so that the triangle formation trails the Earth by 20 degrees. Each spacecraft will contain two independent instruments containing a proof mass, laser and 30 cm diameter telescope for the transmission and reception of laser signals. Two independent Michelson interferometers will be formed, allowing both polarizations of gravitational waves to be detected. The observed signals will yield unique information about the formation of massive black holes and the nature of gravity in the high-field limit.

Folkner, W. M.↗
NASA NTRS2000

The NASA Inductrack Model Rocket Launcher at the Lawrence Livermore National Laboratory

The Inductrack magnetic levitation system, developed at the Lawrence Livermore National Laboratory, is being studied for its possible use for launching rockets. Under NASA sponsorship, a small model system is being constructed at the Laboratory to pursue key technical aspects of this proposed application. The Inductrack is a passive magnetic levitation system employing special arrays of high-field permanent magnets (Halbach arrays) on the levitating carrier, moving above a "track" consisting of a close-packed array of shorted coils with which are interleaved with special drive coils. Halbach arrays produce a strong spatially periodic magnetic field on the front surface of the arrays, while canceling the field on their back surface. Relative motion between the Halbach arrays and the track coils induces currents in those coils. These currents levitate the carrier cart by interacting with the horizontal component of the magnetic field. Pulsed currents in the drive coils, synchronized with the motion of the carrier, interact with the vertical component of the magnetic field to provide acceleration forces. Motional stability, including resistance to both vertical and lateral aerodynamic forces, is provided by having Halbach arrays that interact with both the upper and the lower sides of the track coils. In its completed form the model system that is under construction will have a track approximately 100 meters in length along which the carrier cart will be propelled up to peak speeds of Mach 0.4 to 0.5 before being decelerated. Preliminary studies of the parameters of a full-scale system have also been made. These studies address the problems of scale-up, including means to simplify the track construction and to reduce the cost of the pulsed-power systems needed for propulsion.

Tung, L. S.↗
NASA NTRS2001

A Magnetoresistive Heat Switch for the Continuous ADR

In compensated elemental metals at low temperature, a several Tesla field can suppress electronic heat conduction so thoroughly that heat is effectively carried by phonons alone. In approximately one mm diameter single crystal samples with impurity concentrations low enough that electron conduction is limited by surface scattering, the ratio of zerofield to high-field thermal conductivity can exceed ten thousand. We have used this phenomenon to build a compact, solid-state heat switch with no moving parts and no enclosed fluids. The time scale for switching states is limited by time scale for charging the magnet that supplies the controlling field. Our design and fabrication techniques overcome the difficulties associated with manufacturing and assembling parts from single crystal tungsten. A clear disadvantage of the magnetoresistive switch is the mass and complexity of the magnet system for the controlling field. We have discovered a technique of minimizing this mass and complexity, applicable to the continuous adiabatic demagnetization refrigerator.

Canavan, E. R.↗
NASA NTRS2004

Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

Dennison, J. R.↗
NASA NTRS2007

Effect of Shock on the Magnetic Properties of Pyrrhotite, the Martian Crust, and Meteorites

We performed planar shock recovery experiments on natural pyrrhotite at pressures up to 6.9 GPa. We find that high-field isothermal remanent magnetization in pyrrhotite is demagnetized up to 90% by shock due to preferential removal of low coercivity components of magnetization. Contrary to static experiments, we do not observe complete demagnetization. Post shock permanent changes in magnetic properties include increasing saturation isothermal remanent magnetization, bulk coercivity and lowtemperature memory, and changes in squareness of hysteresis. These changes are consistent with an increase in the volume fraction of single domain grains. The lack of magnetic anomalies over large Martian impact basins is not expected to be solely due to shock demagnetization of the crust. We find that pyrrhotite-bearing rocks and meteorites can retain records of Martian magnetic fields even if shocked to pressures approaching 7 GPa. However, some paleointensity techniques may underestimate this field.

Louzad, Karin L.↗
NASA NTRS2007

INTEGRAL Observations of the Pulsar PSR J1846-0258

We present the results of a study of the high-energy properties of PSR J1846-0258 using INTEGRAL data PSR J1846-0258 has a period of 325 ms and is embedded within a PWN that is associated with the SNR KES 75. This pulsar is unusual for two reasons. First, like Geminga, no radio pulsations have yet been detected from this pulsar. It has thus far been detected exclusively in the X-ray and gamma-ray bands. Second, it has a large inferred magnetic field, approx. 5 x 10(exp 13) G. The 20-200 keV spectra derived from 2.35 Msec of INTEGRAL IBIS/ISGRI observations are consistent with an extension of the previous spectral results at energies below 10 keV from Chandra. The possibility of detecting PSR J1846-0258 with GLAST is discussed as well as the implications a GLAST detection would have on pulsar theory, specifically photon splitting In the magnetospheres of high-field pulsars.

Sturner, Steve J.↗
NASA NTRS2012

Characterization of 4H <000-1> Silicon Carbide Films Grown by Solvent-Laser Heated Floating Zone

Commercially available bulk silicon carbide (SiC) has a high number (>2000/sq cm) of screw dislocations (SD) that have been linked to degradation of high-field power device electrical performance properties. Researchers at the NASA Glenn Research Center have proposed a method to mass-produce significantly higher quality bulk SiC. In order for this bulk growth method to become reality, growth of long single crystal SiC fibers must first be achieved. Therefore, a new growth method, Solvent-Laser Heated Floating Zone (Solvent-LHFZ), has been implemented. While some of the initial Solvent-LHFZ results have recently been reported, this paper focuses on further characterization of grown crystals and their growth fronts. To this end, secondary ion mass spectroscopy (SIMS) depth profiles, cross section analysis by focused ion beam (FIB) milling and mechanical polishing, and orientation and structural characterization by x-ray transmission Laue diffraction patterns and x-ray topography were used. Results paint a picture of a chaotic growth front, with Fe incorporation dependant on C concentration.

Woodworth, Andrew, A↗
NASA NTRS2014

The Neutron Star Zoo

Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not clear how effective it is or on what timescale a buried field might re-emerge. One piece of evidence in favor of accretion-driven field reduction is the fact that NSs in LMXBs, which are older systems (> 108 yr), have mostly low fields and NSs in HMXBs, which are younger systems (107 − 108 yr), have higher fields. This may be an indication that accretion-driven field reduction or decay has not had enough time to operate in HMXBs but has in LMXBs. However, there does not seem to be any evidence of decaying fields in either the LMXB or HMXB populations; e.g. smaller magnetic fields in older systems. On the other hand, CCOs are very young so if they acquired their low fields through mass fallback accretion, the field submergence would have had to operate on much faster timescales than it apparently does in LMXBs. But as we continue to find new species in the NS zoo, one of these may someday be the "Rosetta Stone" that will give us the clues for solving these puzzles.

Zoo↗
NASA NTRS2016

Magnetic Shield Design Modeling and Validation for SWOT Spacecraft Ka-Band Extended Interaction Klystron

Two Extended Interaction Klystrons (EIKs) containing strong permanent magnets were modeled magnetically in a representative spacecraft geometry using commercial finite element modeling techniques and were validated against measurements made at varying distances. Initial modeling results for the 63 A-m2 (amperes per square meter) dipole moment magnets showed that magnetic shields would be necessary in order to meet magnetic field requirements for the Surface Water and Ocean Topography (SWOT) spacecraft, which contains components that are susceptible to external DC (Direct Current) magnetic fields. JPL (Jet Propulsion Laboratory) and the EIK vendor proposed cold rolled steel and mu-metal as potential shield materials along with proposed thicknesses of 0.5 millimeters and 1.5 millimeters. Magnetic shields made from each of these materials were designed and modeled in software, taking high-field saturation into account. Prototype magnetic shields with these parameters were then built, measured with an existing EIK, and compared against modeling results. For single-axis field measurements along the dipole axis, modeling results were within 7 gauss of the measured values at 10 centimeters from the magnet, and converged to less than 1.5 gauss at distances greater than 14 centimeters from the magnet. Three-axis field measurements at locations of interest showed that model correlation improved to within 4 gauss at 11 centimeters and 2 gauss for distances ranging between 15 centimeters and 36 centimeters.

Gonzales, Edward↗
NASA NTRS2017

Magnetic Field Sensing with 4H SiC Diodes: N vs P Implantation

We explore the magnetic sensing capabilities of two 4H-SiC n+p diodes fabricated by NASA Glenn which only differ in the implanted ion species, nitrogen and phosphorus, and the implant activation annealing time. We use low- and high-field electrically detected magnetic resonance (EDMR) to investigate the defect structure used to sense magnetic fields as well as to evaluate the sensitivity. In addition, we expose these devices to high energy electron radiation to evaluate the defect sensing capability in a harsh radiation environment. The results from this work will allow us to tailor our processing methods to design a more optimal 4H-SiC pn diode for magnetic field sensing in harsh environments.

Cochrane, Corey J.↗
DOE OSTI2025

Development of a second COMB dipole magnet with STAR wires

Rare-Earth Barium Copper Oxide (REBCO) coated conductors are an attractive option for application in high-field accelerator magnets due to their high critical field and the convenience of fabrication without heat treatment compared to some other superconductors. Fermilab plays a vital role in superconducting accelerator magnet R&D under the framework of the U.S. Magnet Development Program. An integral part of that program is the accelerator magnet development based on REBCO conductors to demonstrate self-fields of 5 T or greater compatible with operation in hybrid configurations to generate fields beyond 16 T for future High Energy Physics (HEP) applications. A small, two-layer REBCO dipole magnet based on the Conductor on Molded Barrel (COMB) magnet technology, developed at Fermilab with Symmetric Tape Round (STAR®) wires from AMPeers LLC was recently fabricated and tested in liquid helium, demonstrating the design feasibility. A second dipole magnet based on the same technology is currently under development at Fermilab. The coil has a 60-mm clear bore and a 120-mm OD and consists of six layers of STAR® conductor, which allows to significantly increase the magnetic field compared to the previous design, and potentially probe the 5 T self-field target. This presentation reports the progress in the magnet development.

Kashikhin, Vadim [Fermilab]↗
DOE OSTI2025

Overview of the Magnetic Resonance Capabilities at INL

The aim of this presentation is to give a broad overview of the magnetic resonance capabilities at Idaho National Laboratory and how the technique is implemented within the different directorates at the lab. Historically, the high-field NMR instrumentation has been used by our Energy & Environment Science and Technology (EES&T) directorate primarily as a characterization tool for synthetic chemistry work, but we have been actively trying to expand the use of the instrumentation into our Nuclear Science and Technology (NS&T) and National and Homeland Security (NHS) directorates. The expanded scope of work has ranged from solid-state characterization of biomass, analysis of electrolyte materials from lithium ion batteries, quantification of extracted critical materials, and measurement of metal-ligand complexes using ligands proposed for use in the nuclear fuel cycle.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2024

Spatiotemporal dynamics of fast electron heating in solid-density matter via XFEL

Abstract High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗