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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Fluid and hybrid simulations of the ionization instabilities in Hall thruster

Low-frequency axial oscillations in the range of 5–50 kHz stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large-scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insight into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasi-neutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. Further, the predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behavior and the other one, where the low-frequency oscillations coexist with high-frequency oscillations in the range of 100–200 kHz, with the characteristic time scale of the ion channel fly-by time, 100–200 kHz. The other test case demonstrates the effect of a finite temperature of injected neutral atoms, which has a substantial suppression effect on the oscillation amplitude.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1980

Environmental protection of the solar power satellite

This paper examines theoretically several features of the interactions of the Solar Power Satellite (SPS) with its space environment. The leakage currents through the kapton and sapphire solar cell blankets are calculated. At geosynchronous orbit, this parasitic power loss is only 0.7%, and is easily compensated by oversizing. At low-earth orbit, the power loss is potentially much larger (3%), and anomalous arcing is expected for the high-voltage negative surfaces. Preliminary results of a three-dimensional self-consistent plasma and electric field computer program are presented, confirming the validity of the predictions made from the one-dimensional models. Lastly, the paper proposes magnetic shielding of the satellite, to reduce the power drain and to protect the solar cells from energetic electron and plasma ion bombardment. It is concluded that minor modifications from the baseline SPS design can allow the SPS to operate safely and efficiently in its space environment.

Reiff, P. H.↗
NASA NTRS1984

The 3SPACE digitizer: A new input device for solid geometry modeling

The 3SPACE Digitizer is a derivation of SPASYN, which is a patented magnetic transducing system offering an accurate method of calculating the location of one object relative to another. SPASYN uses low-frequency magnetic fields to measure both the position and orientation of its sensor relative to its transmitter. The 3SPACE Digitizer unit consists of a system's electronics unit, a model table, a stylus, and a keypad. In operation, the 3SPACE Digitizer determines the X, Y, Z coordinates of any point located on a low-conductive, three-dimensional model. This data, along with the orientation of the Digitizer's stylus, is immediately available for transmission to a host computer or graphics terminal. Digitization is effected by touching the point to be measured with the tip of a handheld stylus. The 3SPACE Digitizer presents new opportunities for interacting with computers in a large number of engineering and scientific applications. Developed from proven military technology, the 3SPACE Digitizer significantly simplifies three-dimensional digitization and overcomes many of the problems that once plagued such procedures. Its ability to digitize solid objects makes it a valuable new tool for computer-aided design and manufacturing.

Scully, J.↗
DOE OSTI2025

A robust fourth-order finite-difference discretization for the strongly anisotropic transport equation in magnetized plasmas

We propose a second-order temporally implicit, fourth-order-accurate spatial discretization scheme for the strongly anisotropic heat transport equation characteristic of hot, fusion-grade plasmas. Following Du Toit et al. (2018), the scheme transforms mixed-derivative diffusion fluxes (which are responsible for the lack of a discrete maximum principle) into nonlinear advective fluxes, amenable to nonlinear-solver-friendly monotonicity-preserving limiters. The scheme enables accurate multi-dimensional heat transport simulations with up to seven orders of magnitude of heat-transport-coefficient anisotropies with low cross-field numerical error pollution and excellent algorithmic performance, with the number of linear iterations scaling very weakly with grid resolution and grid anisotropy, and scaling with the square-root of the implicit timestep. We propose a multigrid preconditioning strategy based on a lower-order approximation that renders the scheme efficient and scalable under grid refinement. Several numerical tests are presented that display the expected spatial convergence rates and strong algorithmic performance, including fully nonlinear magnetohydrodynamics simulations of kink instabilities in a Bennett pinch in 2D helical geometry and of ITER in 3D toroidal geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Integrated control of edge localized modes and divertor flux using mixed toroidal harmonic resonant magnetic perturbations in EAST

Mixed harmonic resonant magnetic perturbations (RMPs) for integrated edge localized modes (ELMs) and divertor flux control are demonstrated in EAST target plasmas of low input torque and normalized beta β N ~1.7–1.9, which are close to the equivalent value in ITER high Q operation. The applied RMPs are designed to combine a static harmonic of the toroidal mode number n = 3 with a static or rotating harmonic of n = 2. ELM suppression is achieved without a drop of plasma energy confinement, and tungsten concentration is effectively reduced during the application of RMPs. With mixed harmonics, the toroidal varying steady state heat and particle fluxes on the divertor target can be modified with the rotating n = 2 harmonic, which agrees with the numerical modeling of three-dimensional magnetic topology, with plasma responses being taken into account. ELM suppression correlates with the times of larger n = 3 response with mixed n = 2 and n = 3 RMPs. The mixture of harmonics and the rotating n = 2 harmonic does not require additional coil current because the variation is only in the upper-lower coil current phase space. Furthermore, these results further affirm the effectiveness of integrated ELM and divertor flux control using RMPs with mixed harmonics and improve the understanding of the role of plasma responses in ELM suppression.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Charged-particle absorption by Io

An idealized two-dimensional model of the distorted electric field configuration, in the limit of a perfectly conducting satellite or satellite ionosphere, has been constructed. This model has been used to trace the adiabatic guiding-center trajectories of energetic protons and electrons across Jupiter's magnetic-field lines, which are taken as rectilinear. The adiabatic trajectories of very low-energy particles (cold-plasma) are thus found to avoid the satellite and escape absorption. In the limit of very high particle energies the adiabatic trajectories are undistorted, and absorption proceeds as if Io were an insulator. The particle absorbing characteristics of an electrically conducting Jovian satellite are found to depend on both the species and the energy of the incident particle, and the satellite's particle-absorbing cross section differs systematically from its geometric cross section.

Schulz, M.↗
NASA NTRS1983

Numerically simulated two-dimensional auroral double layers

A magnetized 2 1/2-dimensional particle-in-cell system which is periodic in one direction and bounded by reservoirs of Maxwellian plasma in the other is used to numerically simulate electrostatic plasma double layers. For the cases of both oblique and two-dimensional double layers, the present results indicate periodic instability, Debye length rather than gyroradii scaling, and low frequency electrostatic turbulence together with electron beam-excited electrostatatic electron-cyclotron waves. Estimates are given for the thickness of auroral doule layers, as well as the separations within multiple auroral arcs. Attention is given to the temporal modulation of accelerated beams, and the possibilities for ion precipitation and ion conic production by the double layer are hypothesized. Simulations which include the atmospheric backscattering of electrons imply the action of an ionospheric sheath which accelerates ionospheric ions upward.

Borovsky, J. E.↗
DOE OSTI2024

Laser-plasma ion beam booster based on hollow-channel magnetic vortex acceleration

Laser-driven ion acceleration provides ultrashort, high-charge, low-emittance beams, which are desirable for a wide range of high-impact applications. Yet after decades of research, a significant increase in maximum ion energy is still needed. This paper introduces a quality-preserving staging concept for ultraintense ion bunches that is seamlessly applicable from the nonrelativistic plasma source to the relativistic regime. Full three-dimensional particle-in-cell simulations prove robustness and capture of a high-charge proton bunch, suitable for readily available and near-term laser facilities.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Topological kinetic crossover in a nanomagnet array

Ergodic kinetics, which are critical to equilibrium thermodynamics, can be constrained by a system’s topology. Here, we studied a model nanomagnetic array in which such constraints visibly affect the behavior of the magnetic moments. In this system, magnetic excitations connect into thermally active one-dimensional strings whose motion can be imaged in real time. At high temperatures, our data showed the merging, breaking, and reconnecting of strings, resulting in the system transitioning between topologically distinct configurations. Below a crossover temperature, the string motion is dominated by simple changes in length and shape. In this low-temperature regime, the system is energetically stable because of its inability to explore all possible topological configurations. This kinetic crossover suggests a generalizable conception of topologically broken ergodicity and limited equilibration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1971

The X-ray corona and the photospheric magnetic field.

Soft X-ray photographs of the solar corona have been obtained on four flights of a rocket-borne grazing incidence telescope having a resolution of a few arc sec. The configuration of the X-ray emitting structures in the corona has been compared to the magnetic field distribution measured by photospheric longitudinal magnetograms. The X-ray structures trace the three-dimensional configuration of the magnetic field through the lower corona. Active regions in the corona take the form of tubular structures connecting regions of opposite magnetic polarity within the same or adjacent chromospheric active regions. Higher, larger structures link widely separated active regions into complexes of activity covering substantial fractions of the disk. The complexes are separated by areas of low average field in the photosphere. Interconnections across the solar equator appear to originate over areas of preceding polarity.

Krieger, A. S.↗
NASA NTRS2023

Understanding the Deflection of the “Cartwheel CME”: Data Analysis and Modeling

We study the low corona evolution of the “Cartwheel” coronal mass ejection (CME; 2008 April 9) by- reconstructing its three-dimensional path and modeling it with magnetohydrodynamic simulations. This event exhibited a double deflection that has been reported and analyzed in previous works but whose underlying cause remained unclear. The Cartwheel CME traveled toward a coronal hole (CH) and against the magnetic gradients. Using a high-cadence, full-trajectory reconstruction, we accurately determine the location of the magnetic flux rope (MFR) and, consequently, the magnetic environment in which it is immersed. We find a pseudostreamer (PS) structure whose null point may be responsible for the complex evolution of the MFR at the initial phase. From the preeruptive magnetic field reconstruction, we estimate the dynamic forces acting on the MFR and provide a new physical insight into the motion exhibited by the 2008 April 9 event. By setting up a similar magnetic configuration in a 2.5D numerical simulation we are able to reproduce the observed behavior, confirming the importance of the PS null point. We find that the magnetic forces directed toward the null point cause the first deflection, directing the MFR toward the CH. Later, the magnetic pressure gradient of the CH produces the reversal motion of the MFR.

Solar prominences↗
DOE OSTI2020

Magnetic multilayer edges in Bernal-stacked hexagonal boron nitride

Single-layer h-BN is known to have edges with unique magnetism; however, in the commonly fabricated multilayer AA'-h-BN, edge relaxations occur that create interlayer bonds and eliminate the unpaired electrons at the edge. Recently, a robust method of growing the unconventional Bernal-stacked h-BN (AB-h-BN) has been reported. Here, we use theoretical approaches to investigate the nitrogen-terminated zigzag edges in AB-h-BN that can be formed in a controlled fashion using a high-energy electron beam. We find that these "open"edges remain intact in bilayer and multilayer AB-h-BN, enabling researchers potentially to investigate these edge states experimentally. We also investigate the thermodynamics of the spin configurations at the edge by constructing a lattice model that is based on parameters extracted from a set of first-principles calculations. We find that the edge spins in neighboring layers interact very weakly, resulting in a sequence of independent spin chains in multilayer samples. By solving this model using Monte Carlo simulations, we can determine nm-scale correlation lengths at liquid-N 2 temperatures and lower. At low temperatures, these edges may be utilized in magnetoresistance and spintronics applications.

1-dimensional spin chains↗
DOE OSTI2023

Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet Lu y Y 1-y MnO 3

To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of Lu y Y 1-y MnO 3 in detail. The substitutions are adjusted to the Mn atomic position close to x Mn =$\frac{1}{3}$. The neutron powder diffraction data claims that the magnetic structure of Lu y Y 1-y MnO 3 is described as a mixture of Γ 3 (P6' 3 cm') and Γ 4 (P6' 3 c'm) at the x Mn position for y=0.15, 0.30, and 0.45. The ratio of Γ 3 and Γ 4 depends on temperature and composition and the fraction of Γ 3 increases upon cooling, while no clear trimerization was observed at the xMn position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the Γ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in Q and E space of Lu y Y 1-y MnO 3 . We found that Lu 0.3 Y 0.7 MnO 3 could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Accelerating particle-in-cell kinetic plasma simulations via reduced-order modeling of space-charge dynamics using dynamic mode decomposition

We present a data-driven reduced-order modeling of the space-charge dynamics for electromagnetic particle-in-cell (EMPIC) plasma simulations based on dynamic mode decomposition (DMD). The dynamics of the charged particles in kinetic plasma simulations such as EMPIC is manifested through the plasma current density defined along the edges of the spatial mesh. We showcase the efficacy of DMD in modeling the time evolution of current density through a low-dimensional feature space. Not only do such DMD based predictive reduced-order models help accelerate EMPIC simulations, they also have the potential to facilitate investigative analysis and control applications. Here, we demonstrate the proposed DMD-EMPIC scheme for reduced-order modeling of current density and speedup in EMPIC simulations involving electron beam under the influence of magnetic field, virtual cathode oscillations, and backward wave oscillator.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Numerical study of cathode emission constraints on cylindrical self-field MPD thruster performance

A stability equation relating thruster discharge current, argon propellant mass flow rate, and electrode geometry has been solved for a variety of cylindrical self-field MPD thruster configurations and discharge currents. Realistic values for cathode emission current densities were used to provide additional constraints on the thruster geometries. A two-dimensional MPD code was employed to provide better estimates of the maximum achievable specific impulse, thrust, and flow efficiency for cases of interest. The model results indicate that long life, cylindrical self-field MPD thrusters operated with argon propellant may not be able to provide specific impulse values in excess of 2100s. Alternate electrode geometries, applied magnetic fields, and/or low molecular weight propellants may be necessary to achieve higher values of specific impulse.

Lapointe, Michael R.↗
DOE OSTI2020

Examination of Solvent- Room Temperature Ionic Liquid Interactions using 2D NMR and Computational Chemistry

Rare earth metals (REMs) are the key functioning material found in microelectronics, advanced batteries, and high-efficiency electrical motors. Current methods for producing REMs require high temperatures (i.e. energy intensive) and produce an abundance of hazardous fluoride waste. Room temperature ionic liquids (RTILs) are an ideal alternative electrolyte because they allow for a low-temperature, energy-efficient electrochemical process. RTIL properties such as viscosity and conductivity determine how effective they can be in this process. Since viscosity is directly related to both intra and intermolecular forces, this study sets out to investigate two RTILs-Trihexyltetradecylphosphonium dicyanamide (Cyphos 105) and Trihexyltetradecylphosphonium bistrifimide (Cyphos 109) and their interactions. Results from 2-dimensional nuclear magnetic resonance (2D NMR) spectroscopy show that there is an interaction between the tetradecyl tail and the phosphorus atom of the Cyphos RTIL. In order to establish whether this is an intra or an inter-molecular interaction, DFT-based computational calculations were performed to determine the optimized geometry. Calculations were done both in the gas phase and with propylene carbonate as an augmenting solvent. Preliminary results show that there is minimal intramolecular interaction between the tetradecyl tail and the phosphorus atom of the RTILs, and that the interaction seen in the 2D NMR experiment is likely of an intermolecular nature instead.

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

Negatively Charged Excitons in CdSe Nanoplatelets

The low-temperature emission spectrum of CdSe colloidal nanoplatelets (NPLs) consists of two narrow lines. The high-energy line stems from the recombination of neutral excitons. The origin of the low-energy line is currently debated. Here, we experimentally study the spectral shift, emission dynamics, and spin polarization of both lines at low temperatures down to 1.5 K and in high magnetic fields up to 60 T and show that the low-energy line originates from the recombination of negatively charged excitons (trions). This assignment is confirmed by the NPL photocharging dynamics and associated variations in the spectrum. We show that the negatively charged excitons are considerably less sensitive to the presence of surface spins than the neutral excitons. The trion binding energy in three-monolayer-thick NPLs is as large as 30 meV, which is 4 times larger than its value in the two-dimensional limit of a conventional CdSe quantum well confined between semiconductor barriers. A considerable part of this enhancement is gained by the dielectric enhancement effect, which is due to the small dielectric constant of the environment surrounding the NPLs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗