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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Computational investigation of ion cyclotron heating on Proto-MPEX

Ion cyclotron heating (ICH) on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is to be accomplished using the “beach-heating” technique. Beach heating has not been previously demonstrated to efficiently heat core ions at the high electron density values present in Proto-MPEX. This work numerically investigates the wave propagation characteristics of the ICH region on Proto-MPEX to explore avenues for efficient core ion heating. The analysis reveals that finite electron temperature effects are required to predict core ion heating. Cold plasma dispersion analysis and full-wave simulations show that the inertial Alfvén wave (IAW) is restricted from coupling power into the core plasma because (1) the group velocity is too shallow for its energy to penetrate into the core before damping in the periphery and (2) when operating in a magnetic field where ω/ω ci ≳ 0.7, the IAW is cut off from the core plasma by the Alfvén resonance. However, including kinetic effects shows that the kinetic Alfvén wave (KAW) can propagate in the electron temperature regime in Proto-MPEX. Full-wave simulations show that when the electron temperature is increased to T e > 2 eV and the edge electron density is sufficiently high n e edge > 1 × 10 17 m -3 , ion power absorption in the core increases substantially (≈25% of total power). Here, the increase in ion power absorption in the core is attributed to the propagation of the KAW. Calculations of electron and ion power absorption show that the electron heating is localized around the Alfvén resonance, while the ion heating is localized at the fundamental ion cyclotron resonance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

The low-temperature, high-magnetic-field critical current characteristics of Zr-added (Gd, Y)Ba2Cu3Ox superconducting tapes

Critical current performances of state-of-the-art Zr-added (Gd, Y)BaCuO tapes have been investigated over a temperature range of 20-77 K, in magnetic fields up to 9 T and over a wide angular range of magnetic field orientations. The peak in critical current that is commonly observed in the field orientation perpendicular to the tape in BaZrO3 (BZO) containing superconducting tapes is found to vanish at 30 K in magnetic fields at 1-9 T. While the critical current of 15% Zr-added tapes was about 40% lower than that of 7.5% Zr-added tapes at 77 K, the pinning force values of the former were found to be 18-23% higher than those of the latter in the temperature range of 20-40 K and in magnetic fields of 3-5 T. The results from this study emphasize the importance of optimization of coated conductor fabrication processes for optimum performance not just in low magnetic fields at 77 K but also at the operating conditions of low temperatures and high magnetic fields that are of interest, especially for rotating superconducting machinery applications.

Selvamanickam, V↗
DOE OSTI2021

On preheating in Higgs inflation

Abstract Recently, the problem of unitarity violation during the preheating stage of Higgs inflation with a large non-minimal coupling has been much discussed in the literature. We point out that this problem can be translated into a strong coupling problem for the dimensionless effective coupling, and that the existence of these problems is highly dependent on the choice of higher-dimensional operators because they can significantly change the background dynamics and the canonical normalization of the fluctuations around it. Correspondingly, the typical energy of particles produced during the first stage of preheating can remain comparable to or below the cutoff scale of the theory. As an example, we numerically calculate the particle production in the presence of a specific four-derivative operator of the Higgs field, and confirm the statement above. Our argument also applies to multi-field inflation with non-minimal couplings.

Astronomy & Astrophysics↗
DOE OSTI2019

Modeling of high harmonic fast wave scenarios for NSTX Upgrade

NSTX-Upgrade will operate with toroidal magnetic fields ( B T ) up to 1 T, nearly twice the value used in the experiments on NSTX, and the available neutral beam injection (NBI) power will be doubled. The doubling of B T while retaining the 30 MHz RF source frequency has moved the heating regime from the high harmonic fast wave (HHFW) regime used in NSTX to the mid harmonic fast wave regime. By making use of the full wave code AORSA (assuming a Maxwellian plasma), this work explores different HHFW scenarios for two possible antenna frequencies (30 and 60 MHz) and with and without NBI. Both frequencies have large electron absorption for large wave toroidal number particularly without NBI. With the presence of NBI, the fast ions absorption can be dominant in some scenarios. Therefore, a competition between electron and fast ion absorption is clearly apparent partially explaining why in previous NSTX HHFW experiments, a less efficient electron heating was observed. Moreover at the toroidal field of 1 T, a direct thermal ion damping might be possible under the condition when the ion temperature is larger than electron temperature. In general, the electron and ion absorption are found very sensitive to the ratio of electron and ion temperature. The impact of the hydrogen species is also studied showing that, for hydrogen concentration below 2%, the hydrogen absorption is not significant. However, a larger hydrogen concentration could open up new HHFW heating scenarios in NSTX-U. Launching at high toroidal wave number appears to be one way to significantly reduce the ion damping and in turn to obtain large electron damping in the core which can play an important role in the transport studies for NSTX-U. Lastly, an higher magnetic field could also playing a role in increasing the electron temperature and consequently the electron absorption. Indeed a magnetic field scan is also shown and discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Symmetries and anomalies of Hamiltonian staggered fermions

We review the shift (translation) and time reversal symmetries of Hamiltonian staggered fermions and their connection to continuum symmetries concentrating in particular on the case of massless fermions and (3+1) dimensions. We construct operators using the staggered fields that implement these symmetries on finite lattices. We show that shifts composed of an odd multiple of the elementary shift anticommute with time reversal and are related to continuum axial transformations. We argue that the presence of these nontrivial commutation relations implies the existence of lattice ’t Hooft anomalies. From the shifts we also construct a set of conserved, quantized charges that generate continuous symmetries of the lattice theory. In general these do not commute with the vector charge signaling further ’t Hooft anomalies.

Anomalies↗
DOE OSTI2020

Design and demonstration of a distributed-coupling linear accelerator structure

We present a topology for linear accelerators (linacs) in which the power is distributed to the cavities through a waveguide with periodic apertures that guarantees the correct phases and amplitudes along the structure length. Unlike conventional traveling and standing-wave linacs, the presented topology allows the cavity shapes to be designed without the constraints applied to the coupling between cells to transfer power from one cell to the next. Therefore, the topology permits more degrees of freedom for the optimization of individual cavity shapes in comparison with conventional linacs. The cavity shapes can be optimized for power consumption and efficiency, and/or the manipulation of the surface fields for high gradient operation. This topology also provides a possibility for low-temperature manufacturing techniques that prevent the annealing of the material during typical brazing processes; hence, the material could retain its original properties such as hardness. We present a design and an experimental demonstration of this linac.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Spin-Transfer-Torque Oscillator with an Antiferromagnetic Exchange-Coupled Composite Free Layer

We present an antiferromagnetically exchange-coupled composite (soft and hard layers) spin torque oscillator (AF-ECC STO) and demonstrate its operation via both analytical and micromagnetic modeling. The operation exploits the exchange field due to the antiferromagnetic coupling between soft and hard sublayers of the free layer as well as on the easy-plane anisotropy of the soft sublayer. Optimized AF-ECC STO structures can generate large-amplitude magnetization oscillations, which can be tuned over a broad frequency range with precessions mostly generated by the soft layer. We demonstrate that the AF-ECC STO structure offers flexibility in current control of the oscillation frequency and magnetization angle for realistic material parameters.

42 ENGINEERING↗
DOE OSTI2023

Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the $H → WW^* → evμv$ decay channel at 13 TeV with the ATLAS detector

The vector-boson production cross-section for the Higgs boson decay in the H→WW*→eνμν channel is measured as a function of kinematic observables sensitive to the Higgs boson production and decay properties as well as integrated in a fiducial phase space. The analysis is performed using the proton-proton collision data collected by the ATLAS detector in Run 2 of the LHC at $\sqrt{s}$=13 TeV center-of-mass energy corresponding to an integrated luminosity of 139 fb -1 . The different flavor final state is studied by selecting an electron and a muon originating from a pair of W bosons and compatible with the Higgs boson decay. The data are corrected for the effects of detector inefficiency and resolution, and the measurements are compared with different state-of-the-art theoretical predictions. The differential cross-sections are used to constrain anomalous interactions described by dimension-six operators in an Effective Field Theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

On the holographic dual of a topological symmetry operator

We study the holographic dual of a topological symmetry operator in the context of the AdS/CFT correspondence. Symmetry operators arise from topological field theories localized on a subspace of the boundary conformal field theory spacetime. We use bottom up considerations to construct the topological sector associated with their bulk counterparts. In particular, by exploiting the structure of entanglement wedge reconstruction we argue that the bulk counterpart has a nontopological world volume action, i.e., it describes a dynamical object. As a consequence, we find that there are no global 𝑝-form symmetries for 𝑝 ≥ 0 in asymptotically anti–de Sitter spacetimes, which includes the case of noninvertible symmetries. Provided one has a suitable notion of subregion-subregion duality, our argument for the absence of bulk global symmetries applies to more general spacetimes. These considerations also motivate us to consider for general QFTs (holographic or not) the notion of lower-form symmetries, namely, (−𝑚)-form symmetries for 𝑚 ≥ 2.

quantum gravity↗
DOE OSTI2021

Three-Phase LCC-LCC Compensated 50-kW Wireless Charging System with Non-Zero Interphase Coupling

In this paper, an LCC-LCC compensated 50 kW 3phase (3φ) wireless charging system with nonzero interphase mutual inductance is demonstrated. The 3φ-LCC compensation is designed considering a nonzero mutual-inductance among the phase-coils to meet resonance criteria, balance voltages and currents of the resonant tank components, achieve desired voltage gain, and ensure the zero-voltage switching (ZVS) operation. An experimental prototype of the 3φ-LCC-LCC compensation circuit is built for a 50 kW bipolar coil-based 3φ wireless charging system. The prototype system was tested at rated 50 kW power for evaluating the efficiency, ZVS operation, electric and magnetic field emissions, and thermal characteristics. The experimental results show 94.3% dc-to-dc efficiency and only 4.4 μT rms magnetic field emission at the rated 50 kW output power.

Mohammad, Mostak↗
DOE OSTI2023

Reactive Power: sorted, perhaps

The measurement of reactive power has been challenging for over a century. By the 1920s, the IEC and the AIEE were seeking new definitions for reactive power, specifically to handle distorted waveforms and unbalanced systems. Solutions had not and have not been found. This paper shows there are two aspects to the problem. First, the conceptual underpinning of reactive power provides a very shaky foundation for the design of an instrument. Second, the kind of instrument needed is one that has been largely unrecognized in the power engineering field. It is an operational measurement. These aspects of the measurement have been taken into account in IEEE Standard 1459, presently undergoing revision by a working group of the IEEE PES Power System Instrumentation and Measure¬ments Committee.

reactive power, measurement theory, operational, D↗
DOE OSTI2012

Scalable Triadic Analysis of Large-Scale Graphs: Multi-Core vs. Multi-Processor vs. Multi-Threaded Shared Memory Architectures

Triadic analysis encompasses a useful set of graph mining methods that is centered on the concept of a triad, which is a subgraph of three nodes and the configuration of directed edges across the nodes. Such methods are often applied in the social sciences as well as many other diverse fields. Triadic methods commonly operate on a triad census that counts the number of triads of every possible edge configuration in a graph. Like other graph algorithms, triadic census algorithms do not scale well when graphs reach tens of millions to billions of nodes. To enable the triadic analysis of large-scale graphs, we developed and optimized a triad census algorithm to efficiently execute on shared memory architectures. We will retrace the development and evolution of a parallel triad census algorithm. Over the course of several versions, we continually adapted the code’s data structures and program logic to expose more opportunities to exploit parallelism on shared memory that would translate into improved computational performance. We will recall the critical steps and modifications that occurred during code development and optimization. Furthermore, we will compare the performances of triad census algorithm versions on three specific systems: Cray XMT, HP Superdome, and AMD multi-core NUMA machine. These three systems have shared memory architectures but with markedly different hardware capabilities to manage parallelism.

Triadic analysis, triads, triad census, large-scal↗
DOE OSTI2014

Thermal-mechanical properties of epoxy-impregnated Bi-2212/Ag composite

In this study, knowledge of the thermal-mechanical properties of epoxy/superconductor/insulation composite is important for designing, fabricating, and operating epoxy impregnated high field superconducting magnets near their ultimate potentials. We report measurements of the modulus of elasticity, Poisson's ratio, and the coefficient of thermal contraction of epoxy-impregnated composite made from the state-of-the-art powder-in-tube multifilamentary Ag/Bi 2 Sr 2 CaCu 2 O x round wire at room temperature and cryogenic temperatures. Stress-strain curves of samples made from single-strand and Rutherford cables were tested under both monotonic and cyclic compressive loads, with single strands insulated using a thin TiO 2 insulation coating and the Rutherford cable insulated with a braided ceramic sleeve.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The effect of heat treatment on the stability of Nb 3 Sn RRP-150/169 strands

Here, the magnetic stability of superconductor strands and cables is a key issue in the successful building and operation of high-field accelerator magnets. In this paper, we report the study of a state-of-the-art 0.7 mm Nb 3 Sn restacked-rod-process strand manufactured by Oxford Instrument Superconductor Technology. This conductor will be used in Rutherford cable for a 15-T Nb 3 Sn dipole demonstrator being built at Fermi National Accelerator Laboratory. Particularly, this study focuses on the impact of varying heat treatment conditions on the stability of the strand. Both the stability against internal flux jumps and external thermal perturbations are studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Fabrication of Bi-2212 Canted-Cosine-Theta Dipole Prototypes

The U.S. Magnet Development Program (MDP) is exploring the possibility of combining low-and higherature superconductor technologies, using cosine-theta and canted-cosine-theta (CCT) Nb3Sn dipole magnets together with Bi-2212 CCT inserts, with the ultimate goal of constructing a 20-T dipole. The MDP short-term goal is a Bi-2212 CCT insert capable of reaching 5 T in the bore when operating as a stand-alone and 3 T when operating under a background field of 15 T. This paper reports on the fabrication of our BIN4 dipole magnet and our BIN5a and BIN5b coils, designed and built at the Lawrence Berkeley National Laboratory to address potential fabrication issues of Bi-2212 coils and verify the design of our 18-20-T dipole magnet. BIN4 is a two-layer 50-cm-long CCT magnet that uses a nine-strand Rutherford cable made with 0.8-mm-diameter Bi-2212 strands. Its goal is to investigate critical current, insulation integrity, manufacturing challenges, and quench protection issues after heat treating both layers together under oxygen at standard atmosphere (1 bar). BIN5a and BIN5b are two identical coils, similar to the outer layer of BIN4, with the difference that the length is 39 cm, and they will undergo 50-bar overpressure processing heat treatment. Finally, BIN5 coils are made from the state-of-the-art strand with an engineering critical current density of 1150 A/mm 2 at 4.2 K and 5 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Investigation of a nonequilibrium polariton condensate in cylindrical micropillars in a strong magnetic field

We analyze the photoluminescence of a nonequilibrium polariton condensate in cylindrical micropillars etched on the surface of a high-Q GaAs microcavity in a wide range of detunings in a magnetic field up to 12 T for various levels of nonresonant laser pumping by nanosecond pulses. With such a method of excitation, a considerable effect of the interaction of the reservoir of photoexcited excitons with the condensate on the Zeeman splitting of the polariton condensate levels can be expected, which can lead to a decrease in its value and even to sign reversal. However, the measurements of photoluminescence in a wide range of optical excitation densities show that Zeeman splitting weakly depends on the optical pumping (its variation does not exceed 15% of the splitting in a field of 12 T). The estimation of the exciton density in the reservoir based on these data gives a value lower than 10{sup 8} cm{sup –2}. In addition, a noticeable decrease (by a factor of about 1.8) in the polariton condensation threshold in a magnetic field is detected.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Electrodynamic response of charge carriers in doubly periodic semiconductor n-type superlattices in a permanent homogeneous magnetic field

The electromagnetic response of the two-dimensional electron gas of a surface superlattice placed in a perpendicular permanent homogeneous magnetic field is studied. The magneto–optic Kerr and Faraday effects are calculated. The conditions of transparency of model semiconductor structures in the terahertz frequency region are found and the field-induced spin density of the electronic states is calculated. The features of the frequency dependences of complex Kerr and Faraday angles are connected with the symmetry of the spinor states of the charge carriers in a superlattice.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

On the analytical properties of the magneto-conductivity in the case of presence of stable open electron trajectories on a complex Fermi surface

We consider the electric conductivity in normal metals in presence of a strong magnetic field. It is assumed here that the Fermi surface of a metal has rather complicated form such that different types of quasiclassical electron trajectories can appear on the Fermi level for different directions of B. The effects we consider are connected with the existence of regular (stable) open electron trajectories which arise in general on complicated Fermi surfaces. The trajectories of this type have a nice geometric description and represent quasiperiodic lines with a fixed mean direction in the p-space. Being stable geometric objects, the trajectories of this kind exist for some open regions in the space of directions of B, which can be represented by “Stability Zones” on the unit sphere S{sup 2}. The main goal of the paper is to give a description of the analytical behavior of conductivity in the Stability Zones, which demonstrates in general rather nontrivial properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗