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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
NASA NTRS1995

Magnetic reconnection in the presence of sheared flow and density asymmetry: Applications to the Earth's magnetopause

Classical models of magnetic reconnection consist of a small diffusion region bounded by two symmetric slow shocks, across which the plasma is accelerated. Asymmetries often present in space plasmas are sheared plasma flow and dissimilar plasma densities on the two sides of current sheets. In this paper, we investigate magnetic reconnection in the presence of a shear flow and an asymmetric density across the current sheet using two-dimensional magnetohydrodynamic (MHD) simulations. The results demonstrate that magnetic reconnection can occur only for a plasma flow velocity (in the frame of the X line) which is below the Alfven speed in each inflow region. This limits the velocity of the X line to a certain range for a given flow shear and provides an upper limit to the total velocity shear at which reconnection ceases to operate. Depending on the direction of the flow in the adjacent inflow region, the effects from the sheared flow and from the density asymmetry will compete with or enhance each other in respect to the magnitude and location of the currents which bound the outflow regions. The results are applied to the dayside and flank regions of the magnetosphere. For the dayside region where the magnetosheath flow is slow, the magnetic field transition region is thin and the accelerated flow is earthward of the sharp current layer (magnetopause). At the flanks tailward of the X line, shear flow and density asymmetry effects compete making the magnetic field transition layer broad with the high-speed flow contained within the transition region which explains corresponding observations. At the flanks sunward of the X line, shear flow and density asymmetry effects enhance each other and lead to a strong current sheet on the magnetosheath side of the accelerated flow. The total volume affected by magnetic reconnection is much larger than the steady state region. A large bulge region precedes the steady state region. Qualitatively, the bulge and the steady state region have similar signatures and both can explain observations. We provide criteria in order to distinguish between the bulge and the steady state region in observations.

La Belle-Hamer, A. L.↗
DOE OSTI2025

Theory and simulations of cross-beam energy transfer between speckled laser beams

In this paper, we introduce a realistic modeling of laser beams smoothed by random phase plates to investigate cross-beam energy transfer (CBET). We compute the total field of the smoothed laser beams, which allows us to perform accurate simulations and to build a model accounting for the realistic structure of the speckles. This lets us confirm the results already discussed in a previous work given by Oudin et al. [Phys. Plasmas 29, 112112 (2022)]. When CBET is induced by a plasma flow, plane wave models can predict the exchange between smoothed laser beams. By contrast, when the exchange is caused by a wavelength shift between the laser fields of each beam, plane wave models overestimate the energy transfer, even for strongly Landau-damped ion acoustic waves. We also show that the laser angular spread, which results from its focusing, affects the resonance between the ponderomotive force induced by the laser fields and the ion acoustic wave. It increases the resonance width, which weakly depends on the Landau damping rate when there is a wavelength shift and no flow. In addition, the power transfer obtained with or without a phase plate is essentially the same in the perturbative regime and for small crossing angles.

Laser plasma interactions↗
DOE OSTI2020

Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D

Impurity seeding studies in the slot divertor (SAS) at DIII-D have revealed a strong relationship between the detachment onset and pedestal characteristics with both target geometry and impurity species. N 2 seeding in the slot has led to the first simultaneous observation of detachment on the entire suite of boundary diagnostics viewing the SAS without degradation of core confinement. SOLPS-ITER simulations with D+C+N, full cross-field drifts and n-n collisions activated are performed for the first time in DIII-D to interpret the behavior. This illustrates a strong effect of divertor configuration and plasma drifts on the recycling source distribution with significant consequences on plasma flows. Flow reversal is found for both main ions and impurities affecting strongly the impurity transport and providing an explanation for the observed dependence on strike point location of the detachment onset and impurity leakage found in the experiments. Matched discharges with either nitrogen or neon injection show that while nitrogen does not significantly affect the pedestal, neon leads to increased pedestal pressure gradient and improved pedestal stability. Little nitrogen penetrates in the core, but a great amount of neon is found in the pedestal consistent with the different ionization potentials of the two impurities. This research demonstrates that neutral and impurity distributions in the divertor can be controlled through variations in strike point locations in a fixed baffle structure. Divertor geometry combined with impurity seeding enables mitigated divertor heat flux balancing core contamination and thus leading to enhanced divertor dissipation and improved core-edge compatibility which are essential for ITER and for future fusion reactors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Quadrupolar density structures in driven magnetic reconnection experiments with a guide field

Magnetic reconnection is a ubiquitous process in plasma physics, driving rapid and energetic events such as coronal mass ejections. Reconnection between magnetic fields with arbitrary shear can be decomposed into an anti-parallel reconnecting component and a non-reconnecting guide-field component, which is parallel to the reconnecting electric field. This guide field modifies the structure of the reconnection layer and the reconnection rate. We present results from experiments on the MAIZE pulsed-power generator (500 kA peak current, 200 ns rise time), which use two exploding wire arrays, tilted in opposite directions, to embed a guide field in the plasma flows with a relative strength b≡B g /B rec =0, 0.4, or 1. The reconnection layers in these experiments have widths that are less than the ion skin depth, d i =c/ω pi , indicating the importance of the Hall term, which generates a distinctive quadrupolar magnetic field structure along the separatrices of the reconnection layer. Using laser imaging interferometry, we observe quadrupolar structures in the line-integrated electron density, consistent with the interaction of the embedded guide field with the quadrupolar Hall field. Our measurements extend over much larger length scales (40d i ) at higher β (∼1) than previous experiments, providing an insight into the global structure of the reconnection layer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Particle dynamics in the spatial afterglow of flowing dusty plasmas

Final technical report for project Department of Energy - DE-SC0022242. The overarching hypothesis of this project was that the particle dynamics in the afterglow of dusty plasmas are determined by the interplay of the transient plasma properties and the material properties of dust particles. By combining experiments and modeling in an approach fundamentally different from prior research, this project investigated correlations between material properties and basic dust charging and decharging mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1973

Effects of interhemisphere transport on plasma temperatures at low latitudes.

The thermal balance of the equatorial plasma between 300 and 800 km is examined. Steady state nighttime calculations are made for O+, H+, and electrons. The following features are included: collisional heat transfer between ions, electrons, and neutrals; ion and electron thermal conduction along the field lines; curvature of the field lines; nonlinear advection due to field-aligned ion and electron motions; and convective compression or expansion due to field-aligned and E x B motions. The ion velocities necessary to calculate the effects of convection are obtained from the work of Moffett and Hanson, who include a meridional wind across the magnetic equator in their calculations. It is shown that field-aligned interhemisphere plasma flows appreciably affect the plasma temperatures.

Bailey, G. J.↗
NASA NTRS1976

Evidence of outward flow of plasma in a coronal hole

The solar spectrum was photographed in the range 200-700 A with a grazing-incidence stigmatic rocket spectrograph. Doppler shifts of the three coronal lines Si XI (303 A), Mg X (610 A), and Mg IX (368 A) were measured for various regions of the solar disk, including a coronal hole. From the relative shifts in the latter region, an average outward velocity of 16 km/s was computed for the plasma in the coronal hole. The full widths at half-maximum for the above lines were appreciably less in the coronal-hole region than in a quiet region, indicating a lower temperature in the hole. Both the measured velocity and the temperature results are consistent with solar-wind data and with current theories of coronal holes.

Cushman, G. W.↗
NASA NTRS1981

Applications of the concept of generalized vorticity to space plasmas

A reformulation of the momentum equation for electrons or ions in a collisionless plasma leads to an equation which describes the behavior of the plasma in terms of a generalized vorticity. This vorticity is both divergence-free and conserved along plasma flow streamlines. When the plasma has zero vorticity, a special relation is established which appears to have application to small scale magnetic features within both conventional space plasmas and superconductors.

Banks, P. M.↗
NASA NTRS1981

Multiple crossings of a very thin plasma sheet in the earth's magnetotail

High resolution magnetic field, thermal plasma, and energetic particle data measured on the IMP 8 spacecraft are used to demonstrate that a thin plasma sheet with rapidly flowing plasma undergoes violent oscillatory motion that causes the entire thickness of the plasma sheet to pass over the spacecraft in times which are sometimes as short as 10 s. Ions with 50 and 290 keV energy are investigated since their gyroradii are comparable to the plasma sheet thickness. As the spacecraft moves from the plasma sheet into the lobe, the energetic particle intensities decrease, but the 290 keV ions are relatively more numerous than 50 keV ions on field lines located deeper in the lobe.

Fairfield, D. H.↗
NASA NTRS1984

The flow of plasma in the solar terrestrial environment

The development of electric fields in an expanding plasma was studied. With regard to the polar wind, it was found that hot magnetospheric electrons have a pronounced effect on the polar wind. In addition, there is no O(+) charge exchange barrier and substantial fluxes of O(+) ions can escape with the polar wind. In the auroral plasma physics area, the excitation of electrostatic waves by field aligned auroral electron beams was examined. It was demonstrated that the auroral field aligned current density can be large enough to excite Buneman double layers. For situations that lead to strong double layers, it was shown that the temporal evolution of the potential profile is controlled by current fluctuations. Two dimensional particle in cell simulations were conducted, and the high frequency wave turbulence excited by an auroral electron beam of finite width perpendicular to an ambient magnetic field was investigated. The formation of V shaped auroral potential structures was studied, and numerical simulations of double layers and auroral electric fields were reviewed.

Schunk, R. W.↗
NASA NTRS1989

Analysis of an extended period of earthward plasma sheet flow at about 220 R(E) - CDAW 8

The interpretation of the ISEE 3 earthward flow events observed during an extended period on January 29, 1983 is addressed in terms of a neutral line moving beyond roughly 220 earth radii. This concept was tested for consistency with current magnetospheric and solar wind observations. A broad range of additional data including Dynamics Explorer auroral imaging and a wide variety of ground-based measurements from the eighth Coordinated Data Analysis Workshop (CDAW 8) was available. The distant neutral line location within the context of the distant tail, geostationary orbit, auroral zone, and associated solar wind data is analyzed, based on an extended version of the Coraniti and Kennel (1972) flaring tail theory. It is concluded, from known solar wind conditions that, for a typical neutral line location at about 135 earth radii, an increase of about 30 percent of the near-earth lobe field strength would be required to cause the distant neutral line to move tailward beyond 220 earth radii. The question of why substorms did not terminate the growth phase earlier is also addressed.

Schindler, K.↗
NASA NTRS1990

The average tangential electric field at the noon magnetopause

Two hundred and five magnetopause passes of the ISEE 1 satellite through the magnetopause within 2 hrs of local noon during the time period 1977-1981 were examined in order to determine the relationship between the dawn-dusk tangential electric field at the magnetopause and the northward component of the magnetosheath magnetic field; the ratio of these quantities yields the speed of the plasma flow toward the magnetopause (i.e., the reconnection flow speed). The results indicate that, on the average, reconnection occurs at the subsolar magnetopause, and that the average reconnection flow speed of magnetosheath plasma toward the magnetopause is about 15 percent of the local Alfven speed.

Lindqvist, P.-A.↗
NASA NTRS1990

Cosmic-ray gradient measurements and modulation beyond the inner solar wind termination shock

Data provided by the IMP, Voyager, and Pioneer spacecraft for the cosmic-ray particles with E greater than 60 MeV show the existence of integral radial cosmic-ray-density gradients which were nearly constant from 1977 to 1982. In this paper, these measurements are explained using a model in which significant modulation occurs in the turbulent shocked plasma flow between the inner solar wind termination and the outer contact discontinuity separating the interstellar medium flow from the heliospheric plasma.

Quenby, J. J.↗
NASA NTRS1990

Effects of plasma mass flow on Alfven wave phase mixing in coronal loops

Ground-based and space observations suggest that flow phenomena are intrinsic to the solar corona loops. The present analysis addresses flow effects on Alfven wave behavior in coronal loops. The effect of flow on the shear Alfven wave continuum and the associated damping process resulting from phase-mixing is investigated. Flow Doppler-shifts the Alfven wave continuum, thus displacing the range of frequencies for optimum heating. The present study explores Alfven resonance effects on surface waves propagating along coronal loops that are under the influence of flow. Coupling to the Alfven resonance leads to damping of the surface waves. The damping rate in the presence of sub-Alfvenic flows is computed. Flow increases the damping rate of certain modes, thus enhancing the heating effectiveness of those modes. Therefore, these calculations suggest that flow is potentially an important ingredient for an accurate evaluation of heating the solar corona by dissipation of Alfven waves via phase-mixing.

Peredo, M.↗