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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Physics Criteria for a Subscale Plasma Liner Experiment

Spherically imploding plasma liners, formed by merging hypersonic plasma jets, are a proposed standoff driver to compress magnetized target plasmas to fusion conditions. Here, in this paper, the parameter space and physics criteria are identified for a subscale, plasma-liner-formation experiment to provide data, e.g., on liner ram-pressure scaling and uniformity, that are relevant for addressing scientific issues of full-scale plasma liners required to achieve fusion conditions. Lastly, based on these criteria, we quantitatively estimate the minimum liner kinetic energy and mass needed, which informed the design of a subscale plasma liner experiment now under development.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Anisotropic Electron Fluid Closure Validated by in Situ Spacecraft Observations in the far Exhaust of Guide-field Reconnection

Anisotropic electron heating predictions of the equations of state of Le et al. (2009); https://doi.org/10.1103/PhysRevLett.102.085001 (“the EoS”) are applied to reconnection in the Earth's magnetosheath. The model is applicable to open systems where electrons are streaming along magnetic field lines into the reconnection region, sourced by fixed external reservoirs of plasma ambient to the reconnection region. While spacecraft observations have previously shown the EoS to hold in the region near the X-line, we find that for an event observed far downstream (~100 d i ) from the X-line both inflows and the exhaust follow the predictions of the EoS. Furthermore, the model underlying the EoS is extended to include additional perpendicular heating terms relevant to the considered event undergoing active magnetic compression with local electron trapping. Finally, the agreement between the spacecraft observations and the EoS emphasizes the roles of the ambient plasma sources and the dynamics of trapped and passing electrons in setting and controlling the anisotropic electron heating at large scale in naturally occurring plasma configurations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Strong collisionless coupling between an unmagnetized driver plasma and a magnetized background plasma

Fast-exploding plasmas traveling though magnetized, collisionless plasmas can occur in a variety of physical systems, such as supernova remnants, coronal mass ejections, and laser-driven laboratory experiments. To study these systems, it is important to understand the coupling process between the plasmas. Here, in this work, we develop a semi-analytical model of the parameters that characterize the strong collisionless coupling between an unmagnetized driver plasma and a uniformly and perpendicularly magnetized background plasma. In particular, we derive analytical expressions that describe the characteristic diamagnetic cavity and magnetic compression of these systems, such as their corresponding velocities, the compression ratio, and the maximum size of the cavity. The semi-analytical model is compared with collisionless 1D particle-in-cell simulations and experimental results with laser-driven plasmas. The model allows us to provide bounds for parameters that are otherwise difficult to diagnose in experiments with similar setups.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Kinetic simulations of collision-less plasmas in open magnetic geometries

Laboratory plasmas in open magnetic geometries can be found in many different applications such as (a) scrape-of-layer (SOL) and divertor regions in toroidal confinement fusion devices, (b) linear divertor simulators, (c) plasma-based thrusters and (d) magnetic mirrors etc. A common feature of these plasma systems is the need to resolve, in addition to velocity space, at least one physical dimension (e.g. along flux lines) to capture the relevant physics. In general, this requires a kinetic treatment. Fully kinetic particle-in-cell (PIC) simulations can be applied but at the expense of large computational effort. A common way to resolve this is to use a hybrid approach: kinetic ions and fluid electrons. In the present work, the development of a hybrid PIC computational tool suitable for open magnetic geometries is described which includes (a) the effect of non-uniform magnetic fields, (b) finite fully-absorbing boundaries for the particles and (c) volumetric particle sources. Analytical expressions for the momentum transport in the paraxial limit are presented with their underlying assumptions and are used to validate the results from the PIC simulations. A general method is described to construct discrete particle distribution functions in a state of mirror-equilibrium. This method is used to obtain the initial state for the PIC simulation. Collisionless simulations in a mirror geometry are performed. The results show that the effect of magnetic compression is correctly described and momentum is conserved. The self-consistent electric field is calculated and is shown to modify the ion velocity distribution function in a manner consistent with analytic theory. Based on this analysis, the ion distribution function is understood in terms of a loss-cone distribution and an isotropic Maxwell-Boltzmann distribution driven by a volumetric plasma source. Finally, the inclusion of a Monte Carlo based Fokker-Planck collision operator is discussed in the context of future work.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Gyrokinetic simulation of low-frequency Alfvénic modes in DIII-D tokamak

Global gyrokinetic simulations find that a beta-induced Alfvén eigenmode (BAE) and a Low frequency mode (LFM) coexist in the DIII-D tokamak experiments. The LFM can be excited without fast ions and has a frequency inside the gap of the beta-induced Alfvén-acoustic eigenmode (BAAE). The mode structure of the LFM from simulations and many of its parametric dependencies are consistent with experimental observations. For the BAE, the simulated mode structure is consistent with experiment but the frequency is lower than experiment. An antenna scan shows that the LFM is NOT the conventioanl BAAE; rather, it is an interchange-like electromagnetic mode excited by non-resonant drive of pressure gradients. The compressible magnetic perturbations significantly increase the growth rates of the BAE and LFM. On the other hand, effects of trapped electrons and equilibrium current have modest effects on the BAE and LFM. Finally, radial transfer of wave energy is different between the BAE and LFM, resulting in their respective triangular and elliptic mode shapes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Linear gyrokinetic simulations of reversed shear Alfvén eigenmodes and ion temperature gradient modes in DIII-D tokamak

Abstract Global linear gyrokinetic simulations using realistic DIII-D tokamak geometry and plasma profiles find co-existence of unstable reversed shear Alfvén eigenmodes (RSAE) with low toroidal mode number n and electromagnetic ion temperature gradient (ITG) instabilities with higher toroidal mode number n . For intermediate n = [10, 12], RSAE and ITG co-exist and overlap weakly in the radial domain with similar growth rates but different real frequencies. Both RSAE and ITG growth rates decrease less than 5% when compressible magnetic perturbations are neglected in the simulations. The ITG growth rates increase less than 7% when fast ions are not included in the simulations. Finally, the effects of trapped electrons on the RSAE are negligible.

Physics↗
DOE OSTI2017

Experiment to Form and Characterize a Section of a Spherically Imploding Plasma Liner

Here, we describe an experiment to form and characterize a section of a spherically imploding plasma liner by merging six supersonic plasma jets that are launched by newly designed contoured-gap coaxial plasma guns. This experiment is a prelude to forming a fully spherical imploding plasma liner using many dozens of plasma guns, as a standoff driver for plasma-jet-driven magneto-inertial fusion. The objectives of the six-jet experiments are to assess the evolution and scalings of liner Mach number and uniformity, which are important metrics for spherically imploding plasma liners to compress magnetized target plasmas to fusion conditions. Lastly, this article describes the design of the coaxial plasma guns, experimental characterization of the plasma jets, six-jet experimental setup and diagnostics, initial diagnostic data from three- and six-jet experiments, and the high-level objectives of associated numerical modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Data for "Propagation of EMIC Waves from Shabansky Orbits in the Dayside Magnetosphere"

Full-wave simulations of electromagnetic ion cyclotron waves in a non-dipole compressed magnetic field have been conducted using the Petra-M simulation code. The manuscript investigates the effect of misalignment of the Faraday screen and electron density in the scrape-off layer on the excitation and propagation of fast helicon and slow mode waves.

Magnetosphere: outer↗
DOE OSTI2022

Turbulence and Particle Acceleration in a Relativistic Plasma

Abstract In a collisionless plasma, the energy distribution function of plasma particles can be strongly affected by turbulence. In particular, it can develop a nonthermal power-law tail at high energies. We argue that turbulence with initially relativistically strong magnetic perturbations (magnetization parameter σ ≫ 1) quickly evolves into a state with ultrarelativistic plasma temperature but mildly relativistic turbulent fluctuations. We present a phenomenological and numerical study suggesting that in this case, the exponent α in the power-law particle-energy distribution function, f ( γ ) d γ ∝ γ − α d γ , depends on magnetic compressibility of turbulence. Our analytic prediction for the scaling exponent α is in good agreement with the numerical results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Dual-band Ion-scale Waves in the Solar Wind: Statistical Properties and Comparison with Single-band Ion-scale Waves

We present a comprehensive statistical analysis of ion-scale waves including dual-band ion-scale waves (DBIWs) observed by the Parker Solar Probe in the solar wind. DBIWs are characterized by the simultaneous occurrence of distinct left- and right-handed polarized wave packets at higher and lower frequencies, respectively, in the spacecraft frame, implying the presence of bidirectionally propagating L-mode waves. We identify and compare DBIWs to single-band ion-scale waves (SBIWs) and investigate their spatial distributions, background magnetic field conditions, and associated inertial range turbulence characteristics. We find that DBIWs exhibit a strong preferential occurrence at heliocentric distances between 0.2 and 0.25 au (equivalently 43 and 54 R S ) in contrast to SBIWs, the occurrence rate of which peaks closer to the Sun and decreases with the heliocentric distance. DBIWs are also preferentially observed under conditions of strong Alfvénic turbulence, characterized by low magnetic compressibility and perpendicular-dominant fluctuations. These findings support a scenario in which stochastic ion heating via sufficiently large perpendicular Alfvénic fluctuation generates the ion temperature anisotropies required to excite bidirectional ion cyclotron waves. This work advances our understanding of kinetic wave generation in the solar wind and its connection to large-scale turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1960

PINCH BUCKLING

Plasma buckling by magnetic compression

MAGNETOHYDRODYNAMICS↗
NASA NTRS1973

Effects on the geomagnetic tail at 60 earth radii of the geomagnetic storm of April 9, 1971.

A geomagnetic storm beginning with an sc occurred on Apr. 9, 1971. During the storm the charged particle lunar environment experiment at the Apollo 14 site, the solar wind spectrometer experiment at the Apollo 12 site, and the Ames magnetometers on Explorer 35 took data in the magnetosheath, at the magnetopause, in the plasma sheet, and in the high-latitude geomagnetic tail. The MIT Faraday cup and Ames magnetometers on board Explorer 33 monitored the solar wind. The data show that the storm was caused by a corotating tangential discontinuity in the solar wind, the magnetopause position is strongly dependent on the attack angle of the solar wind, and the tail field strength was indirectly measured to increase from 10 to 14 gamma after the sc. During the main phase the field strength in the tail was observed to increase to between 28 and 34 gamma. This increase is consistent with a thermal and magnetic compression of the tail radius from about 26 to about 16 earth radii.

Burke, W. J.↗
NASA NTRS1984

MHD stability of compressible coronal loops with radiative energy loss

The effect of radiative energy loss on the stability of compressible plasma in coronal loops is studied. By taking the limit as poloidal wavenumber m approaches infinity, stability conditions for local modes are derived. It was found that the radiation effect can trigger MHD instabilities of coronal loops which are in ideally marginally stable states. Compressibility is a stabilizing effect for ideal MHD local modes because the compression of magnetic field lines exerts a restoring force by increasing magnetic pressure. Compression of plasma induces two modes in a radiatively unstable plasma, magnetosonic and condensation modes. Compressibility affects the stability of ideally stable (or unstable) coronal plasmas through magnetosonic modes, which are a stabilizing (destabilizing) effect for ideally stable (unstable) plasmas. For coronal plasmas in ideally marginally stable states, condensation as well as magnetosonic modes can trigger MHD instability. Because of these two modes, the effect of radiation on compressible coronal plasmas is more destabilizing than it is on incompressible plasmas when the plasmas are in ideal MHD unstable or marginally stable states.

An, C.-H.↗
NASA NTRS1984

The Solar Maximum observatory

The successful retrieval and repair of the Solar Maximum Mission (SMM) satellite by Shuttle astronauts in April 1984 permitted continuance of solar flare observations that began in 1980. The SMM carries a soft X ray polychromator, gamma ray, UV and hard X ray imaging spectrometers, a coronagraph/polarimeter and particle counters. The data gathered thus far indicated that electrical potentials of 25 MeV develop in flares within 2 sec of onset. X ray data show that flares are composed of compressed magnetic loops that have come too close together. Other data have been taken on mass ejection, impacts of electron beams and conduction fronts with the chromosphere and changes in the solar radiant flux due to sunspots.

Rust, D. M.↗
NASA NTRS1984

Large-scale flow in the dayside magnetosheath

The degree of control over plasma flow direction exerted by the compressed magnetic field in the dayside magnetosheath is examined by comparing ISEE 1 LEPEDEA data with hydrodynamic and MHD predictions. In 11 of 20 observed cases, the flow pattern followed the predictions of simple hydrodynamic theory; in the nine other cases, the flow deviated from this pattern. One case with large deflection was persistent over 1.5 hr, and its direction was consistent with a stagnation point displacement resulting from increased, asymmetric magnetic field pressure contributions during periods of low Alfven Mach number. The eight other cases of observed large deflection are consistent with either the subsolar merging line or the antiparallel merging hypothesis, but not exclusively with one or the other.

Crooker, N. U.↗
NASA NTRS1987

On magnetohydrodynamic solitons in jets

Nonlinear solitary wave propagation in a compressible magnetic beam model of an extragalactic radio jet is examined and shown to lead to solitons of the Benjamin-Ono type. A number of similarities between such magnetic beam models of jets and models of solar photospheric flux tubes are pointed out and exploited. A single soliton has the appearance of a symmetric bulge on the jet which propagates faster than the jet's flow.

Roberts, B.↗
NASA NTRS1989

The oblique behavior of low-frequency electromagnetic waves excited by newborn cometary ions

The free energy in oxygen or hydrogen ions freshly created in the solar wind stimulates low-frequency electromagnetic waves whose growth does not always maximize at parallel propagation. Exploration of the wave vector plane discloses the frequent occurrence of islets of oblique growth unconnected to the unstable parallel modes. Contour plots of the growth rate, real frequency, polarization, and magnetic compression characterize the oblique wave behavior for large values of the initial pitch angle of the cometary particles. Although wave-particle (Landau and cyclotron) resonances feed most of the surveyed oblique instabilities, some are seemingly fluidlike. The results, obtained from the numerical solution of the kinetic dispersion and wave equations, imply that newborn ions can easily excite significant oblique hydromagnetic wave activity. Cometary environments provide the adopted plasma model, but the study is helpful in the interpretation of other low-frequency wave observations in space.

Brinca, Armando L.↗