Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETIC DISPERSION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Wave excitation by inhomogeneous suprathermal electron beams

Wave excitation by an inhomogeneous suprathermal electron beam in a homogeneous magnetized plasma is studied. Not only is the beam density nonuniform, but the beam electrons possess a sheared bulk velocity. The general dispersion equation encompassing both electrostatic and electromagnetic effects is derived. Particular attention is given to the whistler mode. It is established that the density-gradient and velocity-shear effects are important for waves with frequencies close to the lower-hybrid resonance frequency.

Freund, H. P.↗
NASA NTRS1983

Density drift instabilities and weak collisions

A model is developed which describes the effects of weak collisions on the linear kinetic theory of electrostatic density drift instabilities. A dispersion equation valid at all frequencies and wave numbers is derived using the assumptions of a weak, uniform density gradient; a uniform magnetic field; and the BGK collision operator with a modification of the local approximation. The properties of the universal and collisional density drift instabilities at maximum growth rates are examined in detail. The thresholds of the instabilities are examined for an ionospheric model which includes ion-neutral, electron-neutral, and electron-ion collisions, and are compared with the threshold of the lower hybrid density drift instability. It is concluded that the k to the -5th short wavelength density power spectra observed above 280 km in the PLUMEX experiment are due to the effects of the universal density drift instability.

Gary, S. P.↗
NASA NTRS1992

Parametric instabilities of large amplitude Alfven waves with obliquely propagating sidebands

This paper presents a brief report on properties of the parametric decay and modulational, filamentation, and magnetoacoustic instabilities of a large amplitude, circularly polarized Alfven wave. We allow the daughter and sideband waves to propagate at an arbitrary angle to the background magnetic field so that the electrostatic and electromagnetic characteristics of these waves are coupled. We investigate the dependance of these instabilities on dispersion, plasma/beta, pump wave amplitude, and propagation angle. Analytical and numerical results are compared with numerical simulations to investigate the full nonlinear evolution of these instabilities.

Vinas, A. F.↗
NASA NTRS1993

Casting of superconducting composite materials (M-4)

An aluminum-lead-bismuth alloy is a flexible alloy and is promising for easily workable embedded-type, filament-dispersed superconducting wire material. It is difficult to produce homogeneous ingots of this material because it is easily separated into elements when melted on Earth due to the large specific gravity differences. In this experiment, a homogeneous alloy will first be produced in molten state in microgravity. It will then be returned to Earth and processed into a wire or tape form. It will then be dispersed as the second phase in micro texture form into the primary phase of aluminum. Superconducting wire material with high-critical-magnetic-field characteristics will be produced. The texture of the material will be observed, and its performance will be evaluated. In addition to the above alloy, a four-element alloy will be produced from silver, a rare Earth element, barium, and copper. The alloys will be oxidized and drawn into wire after being returned to Earth. The materials are expected to be forerunners in obtaining superconducting wire materials from oxide superconductors.

Togano, Kazumasa↗
NASA NTRS1995

Penetration of the interplanetary magnetic field B(sub y) magnetosheath plasma into the magnetosphere: Implications for the predominant magnetopause merging site

Magnetosheath plasma peertated into the magnetospere creating the particle cusp, and similarly the interplanetary magnetic field (IMF) B(sub y) component penetrates the magnetopause. We reexamine the phenomenology of such penetration to investigate implications for the magnetopause merging site. Three models are popular: (1) the 'antiparallel' model, in which merging occurs where the local magnetic shear is largest (usually high magnetic latitude); (2) a tilted merging line passing through the subsolar point but extending to very high latitudes; or (3) a tilted merging line passing through the subsolar point in which most merging occurs within a few Earth radii of the equatorial plane and local noon (subsolar merging). It is difficult to distinguish between the first two models, but the third implies some very different predictions. We show that properties of the particle cusp imply that plasma injection into the magnetosphere occurs most often at high magnetic latitudes. In particular, we note the following: (1) The altitude of the merging site inferred from midaltitude cusp ion pitch angle dispersion is typically 8-12 R(sub E). (2) The highest ion energy observable when moving poleward through the cusp drops long before the bulk of the cusp plasma is reached, implying that ions are swimming upstream against the sheath flow shortly after merging. (3) Low-energy ions are less able to enter the winter cusp than the summer cusp. (4) The local time behavior of the cusp as a function of B(sub y) and B(sub z) corroborates predictions of the high-latitude merging models. We also reconsider the penetration of the IMF B(sub y) component onto closed dayside field lines. Our approach, in which closed field lines ove to fill in flux voids created by asymmetric magnetopause flux erosion, shows that strich subsolar merging cannot account for the observations.

Newell, Patrick T.↗
NASA NTRS1993

Aerospace devices for magnetic replicas

Retained persistent magnetic field has been studied and improved in the superconductor YBa2Cu3O7 (Y123). During the study, trapped magnetic field, B(t), has been increased by over a factor of 10(exp 5). Methods used to improve magnetic field trapping were principally: (1) the adoption of the Melt Texturing process to increase grain size; (2) the addition of excess Y to disperse deposits of Y2BaCuO5 (Y211) and again increase grain size; (3) irradiation with high energy particles including 1H+, 3He++, 4He++, and fission fragments; and (4) utilizing temperatures below 77 K has also been quantified as a way to increase trapped field. In addition, in our study of B(t), we have found laws governing creep, activation, temperature dependence, creep vs. current flow, etc. In the range 20 K less than or equal to T less than or equal to 65 K, and for B less than 10 Tesla, a simple empirical relationship was found: B(trap) (T2) = B(trap) (T1) ((Tc - T2)/(Tc - T1))squared where Tc is the critical temperature. The highest experimental trapped field was B(trap) = 3.96 Tesla, at 65 K. We believe this to be the highest persistent field ever produced, by any method. A two component model of the persistent currents has been developed. This accurately reproduces the data, using as parameters only the magnitude of a constant surface current, J(s), and a constant volume current J(v). The model successfully predicts B(t) (xyz) for the case of maximum trapped field, for all samples observed. It has also been extended to describe the unsaturated case either zero field cooled, or field cooled. Loss of strap with time has been studied for the critical state (Bt,max), and non critical state (Bt less than Bt,max), for times from a few minutes to a few months, for unirradiated material, for irradiation by 1H+, 3He++, 4He++, high z projectiles, and neutrons, and for all materials used in the overall study. We conclude that: (1) multi Tesla trapped fields are attained; (2) fields over 10 T are achievable; (3) creep is not a large problem; (4) application is feasible to motors, generators, magnets for particle beam optics, separators, levitating bearings, energy storage, shielding, and transportation.

Weinstein, Roy↗
NASA NTRS1981

A spectroscopic, photometric, and magnetic study of the starspot on II Pegasi

A description is presented of extensive observations of II Peg during 1977 and 1978, taking into account multicolor broad-band photometry, high-dispersion spectroscopy, low-dispersion spectrophotometry, and Zeeman analysis. During this time the star showed periodic light variations in excess of a 0.4 mag range attributable to the presence of a large starspot or an equivalent nonuniform surface brightness distribution. The high-precision multicolor photometry, which differed greatly from previous photometric results, illustrates that the starspots on II Peg are continually evolving on time scales of approximately 1 year or less. A low-dispersion spectrum of the large spot showed pronounced VO and TiO molecular adsorption features. A high-resolution, high signal-to-noise Reticon spectrum at lambda 6707 does not show any compelling evidence of previously reported lithium in this star.

Vogt, S. S.↗
DOE OSTI2026

Dynamical moment fragmentation in the all-in all-out pyrochlore Nd 2 ⁢Sn 2⁢ O 7

We report single crystal neutron spectroscopy and bulk characterization on hydrothermally grown Nd 2 Sn 2 O 7 , revealing magnetic moment fragmentation embedded within the all-in–all-out ordered state. The spectra reveal a nearly flat band with pinch-point momentum dependence accompanied by dispersive branches that produce half-moon features across multiple Brillouin zones. These defining signatures are captured quantitatively by a minimal dipolar-octupolar spin Hamiltonian, demonstrating excellent agreement between experiment and theory. The higher flat-mode energy helps account for the absence of dynamical interference in prior μSR studies, while the lack of any photon-like excitation imposes strict constraints on the proposed Coulombic antiferromagnet scenario. Furthermore, our results extend moment fragmentation to Nd 2 Sn 2 O 7 and identify it as a clean, tractable platform for quantitative exploration of emergent gauge field physics in frustrated magnets.

DC susceptibility measurements↗
NASA NTRS1997

Sounding of the Cleft Ion Fountain Energization Region

The objectives of the ground-based observations in support of the SCIFER are: Acquire and display ionospheric conditions prior to launch to aid in the establishment of launch criteria in real time. Observers at both stations participated in real-time visual interpretation. Solar wind data from IMP-8 and WIND were acquired and interpreted in real time. Telephonic and data links were established at the observatory for the launch window period. Ground-based observatory countdown and launch criteria were developed. 2) Relate optical and magnetic ionospheric signatures observed from the ground to magnetospheric boundaries in the energetic particle flux measured at the payload. The energetic electron trapping boundary was found to correspond to the equatorward edge of the discrete auroral arcs forming the dayside aurora. The energetic electron trapping boundary was found to correspond to the poleward edge of pulsating aurora. The pulsating aurora was found to correspond to one second bursts of energy-dispersed electrons originating in the equatorial plane. Pulsations at larger intervals corresponded to travel times to the conjugate region and return. The pulsating aurora was also directly linked to the geomagnetic pulsations and traveling magnetic vortices, all occurring equatorward of the trapping boundary. 630 nm emission corresponding to less than 10 eV electron precipitation was observed equatorward of the trapping boundary (L=15) and ascribed to photoelectrons from the sunlit conjugate region. 3) Aid in the interpretation of time/space incongruities in the rocket data. The motion of the payload conjugate across the aurora showed that the payload passed over three distinct arc systems on the poleward side of the trapping boundary. These results were reported in a series of articles to be printed in Geophysical Research Letters on June 15, l996.

Kintner, P.↗
NASA NTRS1976

Field-aligned fluxes in the geomagnetic equator

During 12 electron injection events observed by Explorer 45 during the December, 1971, and February, 1972, in magnetic storms it was found that the lowest observable pitch angle particles (down to 7 degrees in one case) arrived first. Pitch angle dispersion and shell-splitting effects are shown to be inadequate explanations for most of these pitch angle distributions. It is suggested that parallel electric fields may be supplying 1- to 5-keV electrons to the magnetosphere from the ionosphere. Various models of parallel electric fields are discussed.

Semar, C. L.↗
NASA NTRS1986

Fragmented molecular complexes: The role of the magnetic field in feeding internal supersonic motions

A hierarchical structure for molecular complexes in their cold phase i.e., preceeding the formation of massive stars, was derived from extensive large scale CO(13)(J=1=0) observations: the mass is found to be distributed into virialized clouds which fill only a very low fraction approx. 01 of the volume of the complex and are supported against gravity by internal supersonic motions. An efficient mechanism was found to transfer kinetic energy from the orbital motions of the clouds to their internal random motions. The large perturbations of the magnetic field induced at the cloud boundaries by their interactions with their neighbors generate systems of hydromagnetic waves trapped inside the clouds. The magnetic field lines being closely coupled to the gas at the densities which prevail in the bulk of the clouds volume, internal velocity dispersion is thus generated. Some conclusions derived from this data are given.

Falgarone, E.↗
NASA NTRS1992

The dynamic cusp

Results of a study of satellite and ground-based data acquired near the dayside cusp during a period when the IMF was inferred to have a strong northward component are presented. The presence of Pc 1 bursts, Pc 4-5 pulsations, and a tailward traveling twin vortex pattern of ionospheric convection suggests that the magnetosphere may have been temporarily compressed. Magnetic field data acquired at a synchronous altitude from GOES 5 and on the ground from Huanacayo support this suggestion. Plasma with ion dispersion characteristics associated with a cusp during southward IMF was detected by Viking over a 3.5-deg range of latitude. The presence of standing Alfven waves and ring current ions suggests that this 'cusplike' plasma was observed on closed geomagnetic field lines. It is suggested that the magnetosphere, during a northward IMF, is temporarily compressed by a solar wind pressure enhancement that produces the Pc 1 bursts, Pc 4-5 pulsations, and ionospheric vortices.

Potemra, T. A.↗
NASA NTRS1992

Comparison of weakly and strongly nonlinear wave evolution in a dispersive plasma

An investigation of the evolution of strongly nonlinear, low frequency (ion gyrofrequency), parallel propagating wave packets in a dispersive, collisionless, and low beta(= 8piP/B-squared = 0.3) plasma is undertaken using a hybrid numerical code. These strongly nonlinear wave packets have a transverse magnetic field strength, or wave amplitude, which is of order or greater the field strength along the direction of propagation, and their evolution can differ qualitatively from that of weakly nonlinear packets. The development of spreading fast wave (right helicity) and rarefraction regions competes strongly with steepening, and leads to a long time waveform which differs greatly from that for weak nonlinearity. Results are used to suggest that strongly nonlinear wave evolution occurs frequently in the earth's foreshock.

Vasquez, Bernard J.↗
NASA NTRS1995

Non-gyrotropic proton and alpha-particle velocity distributions in the solar wind: TAUS observations and stability analysis

Ion velocity distribution functions have been measured with high time resolution by the TAUS plasma instrument on the PHOBOS mission to Mars in 1989. The unambiguous separation of protons and alpha-particles by TAUS enabled us to study the nonthermal features of their distributions separately and to analyze the stability of the distributions against excitation of waves in the cyclotron-frequency domain. Typical nonthermal features include temperature anisotropies, with T(sub perpendicular) larger than T(sub parallel), and ion beam populations drifting along the local magnetic field direction. Also, distinctly non-gyrotropic alpha-particle velocity distributions were sometimes found. Non-gyrotropy strongly changes the wave dispersion and gives rise to new growing modes, related to the coupling of the standard wave modes existing in gyrotropic plasma. It is found that for the measured non-gyrotropic ion distributions the right-hand polarized wave can also be excited by a temperature anistropy instead of the usual beam drift.

Astudillo, H. F.↗
NASA NTRS1997

Alfvenic Solitons in Ultrarelativistic Electron-Position Plasmas

In electron-positron plasmas some of the plasma modes are decoupled due to the equal charge-to-mass ratio of both species. We derive the dispersion law for a low-frequency, generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field.

Electron-positron plasmas Pulsars Nonlinear Modes↗
NASA NTRS2021

The First Widespread Solar Energetic Particle Event Observed By Solar Orbiter on 2020 November 29

Context. On 2020 November 29, the first widespread solar energetic particle (SEP) event of solar cycle 25 was observed at four widely separated locations in the inner (. 1AU) heliosphere. Relativistic electrons as well as protons with energies > 50MeV were observed by Solar Orbiter (SolO), Parker Solar Probe (PSP), the Solar Terrestrial Relations Observatory (STEREO)-A and multiple near-Earth spacecraft. The SEP event was associated with an M4.4 class X-ray flare and accompanied by a coronal mass ejection (CME) and an extreme ultraviolet (EUV) wave as well as a type II radio burst and multiple type III radio bursts. Aims. We present multi-spacecraft particle observations and place them in context with source observations from remote sensing instruments and discuss how such observations may further our understanding of particle acceleration and transport in this widespread event. Methods. Velocity dispersion analysis (VDA) and time shift analysis (TSA) were used to infer the particle release times at the Sun. Solar wind plasma and magnetic field measurements were examined to identify structures that influence the properties of the energetic particles such as their intensity. Pitch angle distributions and first-order anisotropies were analyzed in order to characterize the particle propagation in the interplanetary medium. Results. We find that during the 2020 November 29 SEP event, particles spread over more than 230° in longitude close to 1AU. The particle onset delays observed at the different spacecraft are larger as the flare–footpoint angle increases and are consistent with those from previous STEREO observations. Comparing the timing when the EUV wave intersects the estimated magnetic footpoints of each spacecraft with particle release times from TSA and VDA, we conclude that a simple scenario where the particle release is only determined by the EUV wave propagation is unlikely for this event. Observations of anisotropic particle distributions at SolO, Wind, and STEREO-A do not rule out that particles are injected over a wide longitudinal range close to the Sun. However, the low values of the first-order anisotropy observed by near-Earth spacecraft suggest that diffusive propagation processes are likely involved.

A Kollhoff↗
NASA NTRS2018

Violation of Field Line Conservation and Associated Spatial Scales in Particle-In-Cell Simulations and MMS Data

For the first time, space flight technology exists to detect, in situ, violation of magnetic field line conservation. The violation of magnetic line conservation on scales smaller than the system size is a necessary and sufficient condition for finite magnetic field reconnection. We demonstrate that violation of line conservation produces a detectable, structured signature both in particle-in-cell simulations of reconnection and in data from the Magnetospheric Multi-Scale mission. In particle-in-cell simulations of asymmetric reconnection, the quantity-which we call M-that identifies this violation achieves significant values in electron skin depth-scale layers that extend away from the separator, with higher values emerging on the low-density, high-magnetic-field side of the current sheet. At the separator, M owes largely to perpendicular gradients in the parallel electric field, while it attains its highest values away from the separator in dispersed, layered structures associated with gradients in the perpendicular nonideal electric field and electron transport. Sub-ion scale bipolar forms of the quantity also appear further from the separator. In two MMS burst data intervals detecting the electron diffusion region, we find that M exceeds measurement uncertainties both at the separator and near the separatrices. One interval has highly sheared reconnecting fields and the other a stronger guide field. For one event, we determine the location and scale of M and the inner electron diffusion region relative to electron outflows and the magnetic separatrices. The measure can therefore serve as a potent diagnostic for magnetic reconnection in space measurements.

Wendel, Deirdre E.↗
NASA NTRS1981

Discrete breakup arcs and kinetic Alfven waves

Attention is confined to the extremely narrow auroral structures whose characteristic dimensions perpendicular to the magnetic fields are of the order of several hundred meters or even less. The starting point of the model used here is the assumption that discrete breakup arcs are caused by a change in the magnetosphere convection pattern that is localized in space. Particular attention is given to the shear Alfven mode. It is proposed that discrete breakup arcs are a direct manifestation of kinetic interaction between charged particles and an 'mhd' perturbation. It is stressed that the model applies only to narrow structures (thickness of the order of the plasma skin depth) and to short-lived phenomena (time scales shorter than a dispersion time). It is shown that a change of convection pattern in a spatially limited region leads to the emission of a shear-Alfven wave packet which propagates along the magnetic field line with a characteristic velocity.

Goertz, C. K.↗