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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Wave-kinetic approach to zonal-flow dynamics: Recent advances

The basic physics of drift-wave turbulence and zonal flows has long been studied within the framework of the wave-kinetic theory. Recently, this framework has been reexamined from first principles, which has led to more accurate yet still tractable “improved” wave-kinetic equations. In particular, these equations reveal an important effect of the zonal-flow “curvature” (the second radial derivative of the flow velocity) on the dynamics and stability of drift waves and zonal flows. Here, we overview these recent findings and present a consolidated high-level picture of (mostly quasilinear) zonal-flow physics within reduced models of drift-wave turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Interaction of solar wind with the magnetopause-boundary layer and generation of magnetic impulse events

The transport of mass, momentum, energy and waves from the solar wind to the Earth's magnetosphere takes place in the magnetopause-boundary layer region. Various plasma processes that may occur in this region have been proposed and studied. In this paper, we present a brief review of the plasma processes in the dayside magnetopause-boundary layer. These processes include (1) flux transfer events at the dayside magnetopause, (2) formation of plasma vortices in the low-latitude boundary layer by the Kelvin-Helmholtz instability and coupling to the polar ionosphere, (3) the response of the magnetopause to the solar wind dynamic pressure pulses, and (4) the impulsive penetration of solar wind plasma filaments through the dayside magnetopause into the magnetospheric boundary layer. Through the coupling of the magnetopause-boundary layer to the polar ionosphere, those above processes may lead to occurrence of magnetic impulse events observed in the high-latitude stations.

Lee, L. C.↗
DOE OSTI2017

Magnetohydrodynamic Modeling of Solar Coronal Dynamics with an Initial Non-force-free Magnetic Field

The magnetic fields in the solar corona are generally neither force-free nor axisymmetric and have complex dynamics that are difficult to characterize. Here we simulate the topological evolution of solar coronal magnetic field lines (MFLs) using a magnetohydrodynamic model. The simulation is initialized with a non-axisymmetric non-force-free magnetic field that best correlates with the observed vector magnetograms of solar active regions (ARs). To focus on these ideas, simulations are performed for the flaring AR 11283 noted for its complexity and well-documented dynamics. The simulated dynamics develops as the initial Lorentz force pushes the plasma and facilitates successive magnetic reconnections at the two X-type null lines present in the initial field. Importantly, the simulation allows for the spontaneous development of mass flow, unique among contemporary works, that preferentially reconnects field lines at one of the X-type null lines. Consequently, a flux rope consisting of low-lying twisted MFLs, which approximately traces the major polarity inversion line, undergoes an asymmetric monotonic rise. The rise is attributed to a reduction in the magnetic tension force at the region overlying the rope, resulting from the reconnection. A monotonic rise of the rope is in conformity with the standard scenario of flares. Importantly, the simulated dynamics leads to bifurcations of the flux rope, which, being akin to the observed filament bifurcation in AR 11283, establishes the appropriateness of the initial field in describing ARs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Growth and nonlinear saturation of electromagnetic ion cyclotron waves in multi-ion species magnetospheric plasma

Here, the growth and saturation of electromagnetic ion cyclotron (EMIC) waves is essential to the magnetospheric dynamics. Determining and isolating the effects of multiple ion parameters such as temperatures, anisotropies, and relative abundances is important for quantifying these processes in the magnetospheric plasma. In order to study these process, we utilize a 2.5–D hybrid model (where ions are modeled with the particle–in–cell (PIC) method, and electrons are modeled as background neutralizing fluid) to study the nonlinear electromagnetic wave–particle interactions of hot H + , cold H + , cold He + , and cold or hot O + ions for a broad range of typical magnetospheric parameters. The excitation of EMIC waves is driven by the temperature anisotropy of hot H + in our model. As a result, we quantify the parametric dependence of the linear growth, the nonlinear saturation level of perpendicular magnetic fluctuations, and the temporal evolution of the ion temperature anisotropies. We establish the relation between key plasma parameters and the saturated EMIC wave power, using either power law fits or a nonlinear regression method. We construct the dispersion relation of the waves using the results of the model and investigate the energy content in the various branches of the dispersion ( k ∥ –ω space), showing that the different modes can generate wave power in different regions of k space. We find that large O + concentration reduces the growth and saturated amplitude of the waves; but the waves are less sensitive to the temperature of the O + in the temperature range relevant to the magnetosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Formation of edge pressure pedestal and reversed magnetic shear due to toroidal rotation in a tokamak equilibrium

Toroidal rotation is well known to play significant roles in the edge transport and L-H transition dynamics of tokamaks. Our recent calculation finds that a sufficiently strong localized toroidal rotation can directly bring out the formation of edge pressure pedestal with reversed magnetic shear that is reminiscent of an H-mode plasma, purely through the effects of toroidal rotation on the tokamak MHD equilibrium itself. In particular, the enhanced edge toroidal rotation enables a substantial peaking of the parallel current profile near edge in higher β regimes, which leads to the flattening or reversal of the local q (safety factor) profile. Here the formation of pressure pedestal along with the reversed magnetic shear region is shown to be the natural outcome of the MHD tokamak equilibrium in a self-consistent response to the presence of a localized toroidal rotation typically observed in H-mode or QH-mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Surface deformation coupled with self-organized pattern on a liquid anode of 1 atm DC glow discharge

Intricate, self-organized plasma structures observed above the surface of a liquid anode of atmospheric DC glow discharge were found to give rise to coherent, organized surface deformation and mechanical wave formation at the plasma–liquid interface. This new phenomenon indicates that the liquid is closely coupled to the plasma by the anode sheath’s electrohydrodynamic (EHD) force. A scientific question then arises: Do surface perturbations, coupled with the nonuniform surface charge distribution, enhance the electric field and induce self-organization? Using the reflective background-oriented schlieren technique, the liquid surface profile under the plasma pattern was measured for the first time. The results show that surface distortions are driven by the repulsive Coulomb force of nonuniform net-negative surface charge acted by the anode sheath field. The impacts of various operating parameters on the patterns and surface waves were examined, revealing the significance of gas heating and liquid charge relaxation time in the pattern formation mechanism. Time-resolved dynamics of a pulsed DC discharge indicated that the surface deformation only appeared after the establishment of plasma patterns. Statistically, the surface wave under the plasma has high wave numbers (8000–16000 m −1 ) and small amplitudes ($<$ 10 µm), generally found in the capillary wave regime. Yet the motion of surface deformations is in tandem with the plasma pattern and exhibits a nondispersive nature of constant phase velocity (0.1–0.4 m s −1 ), suggesting the dominant role of EHD force over the surface tension in the observed surface wave. These results indicate that the deformed liquid surface is driven by the EHD force of the plasma sheath. Although they share a similar geometry, the deformation and wave dynamics of the liquid surface do not stimulate a plasma pattern. Importantly, the complex EHD coupling in the plasma–liquid system raises awareness and new challenges for plasma control engineering, and the quantitative characteristics of the nondispersive surface wave are informative for advancing relevant theory and modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Surface conversion techniques for low energy neutral atom imagers

This investigation has focused on development of key technology elements for low energy neutral atom imaging. More specifically, we have investigated the conversion of low energy neutral atoms to negatively charged ions upon reflection from specially prepared surfaces. This 'surface conversion' technique appears to offer a unique capability of detecting, and thus imaging, neutral atoms at energies of 0.01 - 1 keV with high enough efficiencies to make practical its application to low energy neutral atom imaging in space. Such imaging offers the opportunity to obtain the first instantaneous global maps of macroscopic plasma features and their temporal variation. Through previous in situ plasma measurements, we have a statistical picture of large scale morphology and local measurements of dynamic processes. However, with in situ techniques it is impossible to characterize or understand many of the global plasma transport and energization processes. A series of global plasma images would greatly advance our understanding of these processes and would provide the context for interpreting previous and future in situ measurements. Fast neutral atoms, created from ions that are neutralized in collisions with exospheric neutrals, offer the means for remotely imaging plasma populations. Energy and mass analysis of these neutrals provides critical information about the source plasma distribution. The flux of neutral atoms available for imaging depends upon a convolution of the ambient plasma distribution with the charge exchange cross section for the background neutral population. Some of the highest signals are at relatively low energies (well below 1 keV). This energy range also includes some of the most important plasma populations to be imaged, for example the base of the cleft ion fountain.

Quinn, J. M.↗
NASA NTRS2019

Recent Advances in Our Understanding of the Earth's Radiation Belts

The Earth's radiation belts were discovered by James van Allen more than fifty years ago and are a home to a plethora of fascinating processes ranging from low energy cold plasma to relativistic and ultra-relativistic particle populations. The traditional morphological picture of the radiation belts is that of an outer belt comprising mostly of electrons and an inner belt comprising mostly of protons with a so-called slot region separating the two. The inner belt is somewhat stable, while the outer radiation belt is very dynamical and shows variability in energetic electron populations over a wide range of energies, intensities, and time scales ranging from minutes, days and even years. This variability is due to dynamical processes of energization and loss with a variety of plasma waves playing an important and crucial role. The traditional picture has recently been challenged with new observations coming from the twin spacecraft mission, Van Allen Probes launched in the fall of 2012, which carries a comprehensive suite of instruments that measure particles and plasma waves. In more than 5 years of observations Van Allen Probes has advanced our understanding of fundamental questions regarding the acceleration and loss of outer Van Allen belt electron population. Van Allen Probes observations have also revealed new phenomena such as the "electron Storage ring", and the "impenetrable barrier". This article reviews electron dynamics in the Van Allen belts focusing on van Allen Probes observations and discuss exciting new ways of advancing radiation belt science with CubeSats and CubeSat constellations.

Relativistic electrons↗
DOE OSTI2019

Three-dimensional plasmoid-mediated reconnection and the effect of toroidal guide field in simulations of coaxial helicity injection

Physics of three-dimensional plasmoid-mediated magnetic reconnection during transient Coaxial Helicity Injection (CHI) plasma start-up is explored using nonlinear MHD simulations in a spherical tokamak. We numerically examine (i) the role of three-dimensional magnetic fluctuations arising from current-sheet instabilities on the formation of plasmoid-mediated closed flux surfaces, and (ii) the effect of toroidal guide field on the MHD stability during transient CHI. Here, we find that even in the presence of nonaxisymmetric edge magnetic fluctuations, current-carrying axisymmetric (n = 0) plasmoids are rapidly formed while twisted open field lines are being injected and are merged to form a large current-carrying magnetic bubble for plasma startup in a tokamak. Additionally, it is discovered that the 3-D physics response is drastically different for simulations at a higher toroidal field, and complete stabilization of nonaxisymmetric fluctuations was achieved at a higher toroidal flux.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Amplification of turbulence through multiple planar shocks

We study the amplification of isotropic, incompressible turbulence through multiple planar, collisional shocks, using analytical linear theory. There are two limiting cases we explore. The first assumes shocks occur rapidly in time such that the turbulence does not evolve between shocks. Whereas the second case allows enough time for turbulence to isotropize between each shock. For the latter case, through a quasi-equation-of-state, we show that the weak multishock limit is agnostic to the distinction between thermal and vortical turbulent pressures, like an isotropic volumetric compression. When turbulence does not return to isotropy between shocks, the generated anisotropy—itself a function of shock strength—can feedback on amplification by further shocks, altering choices for maximal or minimal amplification. In addition for this case, we find that amplification is sensitive to the shock ordering. As a result, we map how choices of shock strength can impact these amplification differences due to ordering, finding, for example, shock pairs which lead to identical mean postshock fields (density, temperature, pressure) but maximally distinct turbulent amplification.

Astrophysical fluid dynamics↗
NASA NTRS1974

The design and development of a space laboratory to conduct magnetospheric and plasma research

A design study was conducted concerning a proposed shuttle-borne space laboratory for research on magnetospheric and plasma physics. A worldwide survey found two broad research disciplines of interest: geophysical studies of the dynamics and structure of the magnetosphere (including wave characteristics, wave-particle interactions, magnetospheric modifications, beam-plasma interactions, and energetic particles and tracers) and plasma physics studies (plasma physics in space, wake and sheath studies, and propulsion and devices). The Plasma Physics and Environmental Perturbation Laboratory (PPEPL) designed to perform experiments in these areas will include two 50-m booms and two maneuverable subsatellites, a photometer array, standardized proton, electron, and plasma accelerators, a high-powered transmitter for frequencies above 100 kHz, a low-power transmitter for VLF and below, and complete diagnostic packages. Problem areas in the design of a space plasma physics laboratory are indicated.

Rosen, A.↗
DOE OSTI2017

Study of the prebreakdown stage of a gas discharge in a diode with point cathode by laser probing

The prebreakdown stage of a gas discharge in a diode with strongly overloaded cathode is studied by laser methods (by simultaneous use of multiframe interferometry and shadow and schlieren photographing) at atmospheric pressure. The spatial resolution of the methods is about 20 μm. A probing pulse of a laser (LS-2151 Nd: YAG laser with a half amplitude duration of 70 ps and a pulse energy of up to 40 mJ) is synchronized with a voltage pulse with accuracy of about 1 ns. High field strength at the cathode is achieved due to the use of thin individual metal tips on the electrodes. It is shown that the initial stage of breakdown of a discharge gap is accompanied by the emergence of a dense plasma cloud at the end of a tip with electron density of about 5 × 10{sup 19} cm{sup –3} with a size of tens of microns, as well as by a sharp increase in the total current through the diode. After the emergence of a dense plasma cloud at the end of a cathode tip, a similar cloud is formed on the surface of the anode; sometime later, these clouds join together and form a tubular current channel. The dynamics of the breakdown, as well as the parameters of the plasma are studied by the abovementioned techniques in three independent optical channels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

He bubble-induced phase transformation of W grain boundaries revealed by accelerated molecular dynamics

The growth of He bubbles and the resulting impact on the microstructural evolution of W are of paramount importance to the plasma-facing materials community due to the application of W in Tokamak fusion reactors. Using accelerated molecular dynamics (AMD) techniques, we outline the structural evolution of grain boundaries (GBs) caused by growing He bubbles. It is discovered that when an alternative, low energy, high density GB structure or phase is available, He bubbles can induce a progressive phase transformation of the GB to the higher density phase by the continual nucleation of W Frenkel pairs. Here, we find that the resulting W self-interstitials migrate to sites at the GB which are structurally related to the higher density phase, leading to the transformation. We discuss the implications of this progressive microstructural evolution on the growing He bubble and consider in general how He bubbles will impact the structural evolution of an arbitrary W GB. These findings of GB phase transformation are predicted to impact other damage events in W such as recrystallization, GB migration and defect segregation which must take these findings into account in order to accurately simulate a realistic W microstructure and hence extract experimentally meaningful data.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Center for Tokamak Transient Simulations (RPI Unstructured Mesh Developments for FES SciDAC4 Partnerships) (Final Report)

The goal of this project was the development of unstructured mesh technologies for fusion simulation codes” for FES SciDAC partnerships and to integrate those technologies into the simulation workflows of those partnerships. Specific developments were executed in support of the following FES SciDAC4 partnerships: Partnership Center for High‐fidelity Boundary Plasma Simulation (HBPS), Center for Integrated Simulation of Fusion Relevant RF (RF‐SciDAC), Center for Plasma Surface Interactions: Predicting the Performance and Impact of Dynamic PFC Surfaces (PSI2), and Center for Tokamak Transient Simulations (CTTS). The key unstructured mesh development areas addressed in this project include (i) methods to most effectively perform PIC calculations on unstructured meshes; (ii) creating meshes for fusion systems accounting for any desired level of geometric complexity and providing physics aware mesh configurations, (iii) adapting unstructured meshes to control the discretization errors, (iv) executing unstructured mesh calculations on GPU accelerated systems, (v) supporting physics/application‐specific PIC operations including surface/wall interactions of particles, (vi) providing infrastructure tools to support the interactions of solvers with unstructured meshes, and (vii) providing advanced methods for coupling plasma physics codes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Simulation of edge localized mode heat pulse using drift-kinetic ions and Boltzmann electrons

This article reports on 1D+2V heat pulse propagation studies using the COGENT guiding center kinetic code. The model uses magnetized kinetic ions and a simple Boltzmann electron model. Results agree with previous kinetic and fluid modeling benchmark studies that correspond to the parameters of edge localized modes (ELMs) observed on the JET tokamak. The plasma parameters for the edge pedestal and ensuing ELM dynamics are in the low collisionality regime. Hence, the dominant balance between the assumed Maxwellian ELM source and collisionless parallel advection causes the ion PDF to develop a significantly anisotropic velocity distribution. Adding nonlinear Coulomb ion-ion collisions to the model acts to smooth the sharp features of the ion distribution function, but the anisotropy remains robust due to the low collisionality.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Nonlinear Interactions of Alfven Waves in Multi-ion Plasmas (Final Report)

Alfven waves are of fundamental importance in magnetized plasmas, such as the solar wind and Earth’s magnetosphere. When the wave amplitude is large, nonlinear interactions among waves, such as three wave resonance, dominate the dynamics. The nonlinear process can be used as a diagnosis of the plasma composition because the composition affects the dispersion relation of Alfven waves, especially when the wave frequency is close to ion cyclotron frequencies. Previous experiments on the Large Plasma Device (LAPD) had demonstrated that the relative density of two ion species can be determined by examining nonlinear interaction of two counter-propagating Alfven waves. In this project we extended the study to a plasma with three ion species, where multiple wave bands exist, and more nonlinear interactions are possible. We also investigated the feasibility of launching two co-propagating waves to measure the ion composition. The findings of this study have implication in developing new technology to measure cold ion populations in space plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

The Plasma Wake Downstream of Lunar Topographic Obstacles: Preliminary Results from 2D Particle Simulations

Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).

Zimmerman, Michael I.↗
DOE OSTI2017

Observations of Reconnection Flows in a Flare on the Solar Disk

Magnetic reconnection is a well-accepted part of the theory of solar eruptive events, though the evidence is still circumstantial. Intrinsic to the reconnection picture of a solar eruptive event, particularly in the standard model for two-ribbon flares (CSHKP model), are an advective flow of magnetized plasma into the reconnection region, expansion of field above the reconnection region as a flux rope erupts, retraction of heated post-reconnection loops, and downflows of cooling plasma along those loops. We report on a unique set of Solar Dynamics Observatory /Atmospheric Imaging Assembly imaging and Hinode /EUV Imaging Spectrometer spectroscopic observations of the disk flare SOL2016-03-23T03:54 in which all four flows are present simultaneously. This includes spectroscopic evidence for a plasma upflow in association with large-scale expanding closed inflow field. The reconnection inflows are symmetric, and consistent with fast reconnection, and the post-reconnection loops show a clear cooling and deceleration as they retract. Observations of coronal reconnection flows are still rare, and most events are observed at the solar limb, obscured by complex foregrounds, making their relationship to the flare ribbons, cusp field, and arcades formed in the lower atmosphere difficult to interpret. The disk location and favorable perspective of this event have removed these ambiguities giving a clear picture of the reconnection dynamics.

79 ASTRONOMY AND ASTROPHYSICS↗