Search NASA⌕ Search

SEARCH · Search NASA

Results for “PLASMA LAYER”

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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Thermomechanical Relaxation of Vibrationally Excited NO in a Hypersonic Turbulent Boundary Layer

The effects of thermal nonequilibrium are studied using a DC glow discharge plasma to selectively modify the vibrational temperature of an otherwise cold flow. These experiments were performed at 𝑴=5.7and 𝑹𝒆=6×10 6 /m in the Actively Controlled Expansion tunnel at Texas A&M University on a canonical 2.75° half-angle wedge test article. A∼47 W plasma was generated across spanwise electrodes, and removable trips produced either a laminar or turbulent boundary layer. NO planar laser-induced fluorescence (PLIF) quantified the extent of the NO 𝑿 2 𝚷 (𝒗=1) vibrational perturbation due to the plasma and its subsequent interplay with the boundary layer, the first such data of which the authors are aware. NOPLIF measurements were taken at three locations along the test article, and quasi-temperature measurements are reported at each. Despite not quantifiably perturbing the boundary layer, the plasma was shown to alter the NO vibrational temperature profile therein. Independent analysis of the thermodynamics and fluid mechanics of the system suggests each set of physics could explain the results observed near and far from the wall, respectively.

Casey J. Broslawski↗
NASA NTRS2007

Recent Plasma Observations Related to Magnetic Merging and the Low-Latitude Boundary Layer. Case Study by Polar, March 18, 2006

We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. Magnetosheath-like plasma is frequently observed deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a long period of northward interplanetary magnetic field (IMP) on March 18, 2006, shows injected magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. Our results support the idea of double reconnection under northward IMP on the same group of field lines can provide a source for the LLBL. However, the flow direction of the accelerated magnetosheath ions antiparallel to the local magnetic field and given location of the spacecraft suggest that these two injection sites are located northward of the spacecraft position. Observed convection velocities of the magnetic field lines are inconsistent with those expected for double post-cusp reconnection in both hemispheres. These observations favor a scenario in which a group of newly closed field lines was created by a combination of high shear merging at high latitudes in the northern hemisphere and low shear merging at lower latitudes at the dayside magnetopause.

Chandler, M.↗
NASA NTRS1994

Guest investigator program study: Physics of equatorial plasma bubbles

Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. Our research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz, 1976; Ott, 1978; Kelley and Ott, 1978). Our results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study and modeling of SM-D electric field instrument (EFI) measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge-shaped plasma bubbles. The second topic was pursued because the inability to predict the day-to-day occurrence of plasma bubbles indicated inadequate knowledge of the physics of plasma bubbles. An understanding of bubble formation requires an understanding of the roles of the various terms in the linearized growth rate of the collisional Rayleigh-Taylor instability. In our study, we examined electric-field perturbations found in SM-D EFI data and found that the seeding is more likely to be produced in the E region rather than the F region. The results of this investigation are presented in the Appendix of this report and will be submitted for publication in the Journal of Geophysical Research.

Tsunoda, Roland T.↗
NASA NTRS1987

Weak double layers in the auroral ionosphere

Previous work on the evolution of weak double layers in a hydrogen plasma was extended to include H(+) and O(+) with relative drift. The relative drift between hydrogen and oxygen ions due to a quasi-static parallel electric field gives rise to a strong linear fluid instability which dominates the ion-acoustic mode at the bottom of the auroral acceleration region. This ion-ion instability can modify ion distributions at lower altitudes and the subsequent nonlinear evolution of weak double layers at higher altitudes in the ion-acoustic regime. Ion hole formation can occur for smaller relative electron-ion drifts than seen in previous simulations, due to the hydrogen-oxygen two-stream instability. This results in local modification of the ion distributions in phase space, and a partial filling of the valley between the hydrogen and oxygen peaks, which would be expected at higher altitudes on auroral field lines. The observed velocity diffusion does not necessarily preclude ion hole and double layer formation in hydrogen in the ion-acoustic regime. These simulation results are consistent with the experimentally measured persistence of separate hydrogen and oxygen peaks, and the observation of weak double layers above an altitude of 3000 km on auroral field lines.

Hudson, M. K.↗
NASA NTRS1989

MHD surface waves in high- and low-beta plasmas. I - Normal-mode solutions

Since the first paper by Barston (1964) on electrostatic oscillations in inhomogeneous cold plasmas, it has been commonly accepted that all finite layers with a continuous profile in pressure, density and magnetic field cannot support normal surface waves but instead the waves always decay through phase mixing (also called resonant absorption). The problem is reanalyzed by studying a compressible current sheet of a general structure with rotation of the magnetic field included. All inhomogeneous layers considered in the high-beta plasma limit do not support normal modes. However, in the limit of a low-beta plasma there are some cases when normal-mode solutions are recovered. The latter means that the process of resonant absorption is not common for all inhomogeneous layers.

Musielak, Z. E.↗
NASA NTRS2012

Comparison of Observations of Sporadic-E Layers in the Nighttime and Daytime Mid-Latitude Ionosphere

A comparison of numerous rocket experiments to investigate mid-latitude sporadic-E layers is presented. Electric field and plasma density data gathered on sounding rockets launched in the presence of sporadic-E layers and QP radar echoes reveal a complex electrodynamics including both DC parameters and plasma waves detected over a large range of scales. We show both DC and wave electric fields and discuss their relationship to intense sporadic-E layers in both nighttime and daytime conditions. Where available, neutral wind observations provide the complete electrodynamic picture revealing an essential source of free energy that both sets up the layers and drives them unstable. Electric field data from the nighttime experiments reveal the presence of km-scale waves as well as well-defined packets of broadband (10's of meters to meters) irregularities. What is surprising is that in both the nighttime and daytime experiments, neither the large scale nor short scale waves appear to be distinctly organized by the sporadic-E density layer itself. The observations are discussed in the context of current theories regarding sporadic-E layer generation and quasi-periodic echoes.

Pfaff, R.↗
NASA NTRS1985

Circulation of energetic ions of terrestrial origin in the magnetosphere

Shelley et al. (1972) have first reported that ions of terrestrial origin might represent a nonnegligible component of the hot magnetospheric plasmas. The present paper is concerned with those observational results which provide keys to the circulation of energetic magnetospheric ions of terrestrial origin, taking into account ions having energies greater than approximately 10-100 eV. It is pointed out that these are the ions which might be expected to circulate through the plasma sheet. On the basis of the observed ion composition of plasma storage regions (the plasma sheet and ring current) and the source and transport regions (auroral zone acceleration region, polar cap, boundary layers and magnetotail lobes), it is concluded that during magnetically active periods the primary circulation of energetic terrestrial ions is directly from the auroral acceleraton region into the plasma sheet boundary layer and central plasma sheet.

Shelley, E. G.↗
NASA NTRS1998

Residual Stresses Modeled in Thermal Barrier Coatings

Thermal barrier coating (TBC) applications continue to increase as the need for greater engine efficiency in aircraft and land-based gas turbines increases. However, durability and reliability issues limit the benefits that can be derived from TBC's. A thorough understanding of the mechanisms that cause TBC failure is a key to increasing, as well as predicting, TBC durability. Oxidation of the bond coat has been repeatedly identified as one of the major factors affecting the durability of the ceramic top coat during service. However, the mechanisms by which oxidation facilitates TBC failure are poorly understood and require further characterization. In addition, researchers have suspected that other bond coat and top coat factors might influence TBC thermal fatigue life, both separately and through interactions with the mechanism of oxidation. These other factors include the bond coat coefficient of thermal expansion, the bond coat roughness, and the creep behavior of both the ceramic and bond coat layers. Although it is difficult to design an experiment to examine these factors unambiguously, it is possible to design a computer modeling "experiment" to examine the action and interaction of these factors, as well as to determine failure drivers for TBC's. Previous computer models have examined some of these factors separately to determine their effect on coating residual stresses, but none have examined all the factors concurrently. The purpose of this research, which was performed at DCT, Inc., in contract with the NASA Lewis Research Center, was to develop an inclusive finite element model to characterize the effects of oxidation on the residual stresses within the TBC system during thermal cycling as well as to examine the interaction of oxidation with the other factors affecting TBC life. The plasma sprayed, two-layer thermal barrier coating that was modeled incorporated a superalloy substrate, a NiCrAlY bond coat, and a ZrO2-8 wt % Y2O3 ceramic top coat. We examined the effect on stress during burner rig thermal cycling of the following independent variables: creep in the bond coat and top coat, oxidation, bond coat coefficient of thermal expansion, number of thermal cycles, and interfacial roughness. All these factors were suspected of influencing TBC failure. The model showed that all the material properties studied had a significant effect on the coating's residual stresses if the interface of the bond coat was rough. Bond coat expansion, bond coat oxidation, and bond coat creep had the highest effect on coating stresses, and these were highly interactive. The model also showed that the mechanism of stress generation during thermal cycling changed with the number of thermal cycles. Bond coat and top coat creep dominated stress generation during early thermal cycles, greatly increasing delamination stresses at the peaks of the bond coat. Therefore, creep is the prime driver for delamination cracking early in life, but cracking is limited to the bond coat peak region. Oxidation of the bond coat, on the other hand, tended to dominate stress generation during later cycles by greatly increasing delamination stresses over bond coat valleys. These results indicate that oxidation is the driver for the continued cracking necessary to cause ceramic layer spallation.

Freborg, A. M.↗
NASA NTRS1991

Plasma waves at Venus

Many significant wave phenomena have been discovered at Venus with the plasma wave instrument on the Pioneer Venus Orbiter. It has been shown that whistler-mode waves in the magnetosheath of the planet may be an important source of energy for the topside ionosphere. Plasma waves are also associated with thickening of the ionopause current layer. Current-generated waves in plasma clouds may also provide anomalous resistance resulting in electron acceleration, possibly producing aurora. Ion-acoustic waves are observed in the bow shock, and appear to be a feature of the magnetotail boundary. Lastly, plasma waves have been cited as evidence for lightning on Venus.

Strangeway, R. J.↗
NASA NTRS1983

Magnetic field line reconnection experiments. V - Current disruptions and double layers

An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

Stenzel, R. L.↗
NASA NTRS1990

Plasma contactor research, 1989

The characteristics of double layers observed by researchers investigating magnetospheric phenomena are contrasted to those observed in plasma contacting experiments. Experiments in the electron collection mode of the plasma contacting process were performed and the results confirm a simple model of this process for current levels ranging to 3 A. Experimental results were also obtained in a study of the process of electron emission from a hollow cathode plasma contactor. High energy ions are observed coming from the cathode in addition to the electrons and a phenomenological model that suggests a mechanism by which this could occur is presented. Experimental results showing the effects of the design parameters of the ambient plasma simulator on the plasma potential, electron temperature, electron density and plasma noise levels induced in plasma contacting experiments are presented. A preferred simulator design is selected on the basis of these results.

Williams, John D.↗
NASA NTRS2002

Observations of Closed Structures at the Magnetopause: A Case for Multiple Reconnections

We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that most of LLBL is located on closed magnetic field lines. These observations strongly favor multiple reconnections between magnetosheath and magnetosphereric flux tubes, creating long spiral flux tube islands at the magnetopause. We report evidence for the simultaneous occurrence of magnetic reconnection at multiple points across the magnetopause, as has been proposed and found to occur in magnetopause simulations. The evidence is in the form of highly structured distributions of ions in velocity parallel to the local magnetic field direction, within the magnetopause and low latitude boundary layer region, from the Interball-Tall spacecraft. We interpret these distributions as a natural consequence of the formation of spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath or interplanetary plasma and from the low latitude boundary layer or magnetospheric plasma. We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that most of LLBL is located on closed magnetic field lines. These observations strongly favor multiple reconnection between magnetosheath and magnetospheric flux tubes, creating long spiral flux tube islands at the magnetopause. We report evidence for the simultaneous occurrence of magnetic reconnection at multiple points across the magnetopause, as has been proposed and found to occur in magnetopause simulations. The evidence is in the form of highly structured distributions of ions in velocity parallel to the local magnetic field direction, within the magnetopause and low latitude boundary layer region, from the Interball-Tail spacecraft. We interpret these distributions as a natural consequence of the formation of spiral. We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar.

Vaisberg, O. L.↗
NASA NTRS1979

ISEE 1 and 2 particle observations of outer plasma sheet boundary

Observations of particle structures by a medium-energy particle experiment on the ISEE 1 and 2 spacecraft at a distance of about 20 earth radii in the geomagnetic tail are presented. Comparison of these data with plasma data indicates the existence of a layer of energetic electrons and ions just outside the plasma sheet. The region outside the plasma sheet in the high-latitude lobe is permeated with low-intensity low-energy (about 1.5 KeV) ions. These particle structures have velocities of a few kilometers per second to at least about 60 km/s. Large-scale motions are observed with onset and recovery of substorms. The dimensions of the particle structures are estimated to range from about 200 to 10,000 km at 20 earth radii. The particle structures are dependent upon the energy as well as the species of the particles.

Parks, G. K.↗
NASA NTRS1991

An experimental investigation of hollow cathode-based plasma contactors

Experimental results are presented which describe operation of the plasma environment associated with a hollow cathod-based plasma contactor collecting electrons from or emitting them to an ambient, low density Maxwellian plasma. A one-dimensional, phenomenological model of the near-field electron collection process, which was formulated from experimental observations, is presented. It considers three regions, namely, a plasma cloud adjacent to the contactor, an ambient plasma from which electrons are collected, and a double layer region that develops between the contactor plasma cloud and the ambient plasma regions. Results of the electron emission experiments are also presented. An important observation is made using a retarding potential analyzer (RPA) which shows that high energy ions generally stream from a contactor along with the electrons being emitted. A mechanism for this phenomenon is presented and it involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice. This can result in the development of a region of high positive potential. Langmuir and RPA probe data suggest that both electrons and ions expand spherically from this hill region. In addition to experimental observations, a one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and shown to agree qualitatively with these observations.

Williams, John D.↗
NASA NTRS2000

Observations of an Intermediate Layer During the Coqui II Campaign

NASA sounding rocket 21.114, launched March 7, 1998, during the Coqui II campaign, provided neutral wind and plasma density measurements of a weak intermediate layer. The layer was centered near 140 km and had an approximate peak plasma density of 2200 cc. The measured winds were typically less than 40 m/s, in agreement with wind shear formation theory and coincident density observations. The data obtained during the flight allow us to explore the plasma density structure and wind field morphology of the intermediate layer. Coupled with simultaneous data from Arecibo Observatory, the upleg and downleg density profiles provide three spatially separated measurements that enable the first detailed investigation of the horizontal extent and variation of an intermediate layer.

Bishop, R. L.↗
NASA NTRS1982

Diffusion processes in the magnetopause boundary layer

A quantitative estimate is calculated for the effect of wave-particle scattering on the structure of the magnetopause boundary layer. It is assumed that large cross-B electric fields are absent in the observed penetration of magnetosheath plasma into the magnetopause boundary layer, thus allowing for cross-field transport comparable to 10% of the Bohm diffusion. It is shown that magnetosheath ions, resonant with low frequency electrostatic waves, can account for the typical boundary layer thickness when transported at 10% of the diffusion rate 1000 sq km/sec. The conditions are required to occur at all local times and under all interplanetary conditions. Significant mass and momentum transfer are then possible across the magnetopause when field merging is not occurring.

Tsurutani, B. T.↗
NASA NTRS2001

Plasma and Field Observations at the Day-Side, Equatorial Magnetopause, Boundary Layers and Magnetosphere

The Polar spacecraft's orbit has precessed in latitude to an orientation that places it at the dayside magnetopause every 18 hours. In this configuration the various regions near the magnetopause(LLBL, turbulent boundary layer, magnetosphere, and magnetosheath) are sampled with high temporal and spatial resolution. These observational periods-ranging from several minutes to more than two hours-provide an unprecedented look at plasma conditions in these regions. Initial analysis of the low-energy ion data from TIDE reveal plasmaspheric-like ions within the turbulent boundary layer. Within this layer, circularly polarized waves accelerate these ions to 30-40 kilometers per second perpendicular to the local magnetic field. These relatively high velocities allow the H(+) to be observed above the -2V spacecraft potential. They also put the low-density O(+) in the higher-energy, higher sensitivity channels such that densities of order 10e-2 can be observed.

Chandler, M. O.↗