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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Benchmarking semiclassical approaches to strong-field QED: Nonlinear Compton scattering in intense laser pulses

The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore, these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here, we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes a0 > 5. We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Characterization of high-frequency waves in the Martian magnetosphere

Context.Various high-frequency waves in the vicinity of upper-hybrid and Langmuir frequencies are commonly observed in different space plasma environments. Such waves and fluctuations have been reported in the magnetosphere of the Earth, a planet with an intrinsic strong magnetic field. Mars has no intrinsic magnetic field and, instead, it possesses a weak induced magnetosphere, which is highly dynamic due to direct exposure to the solar wind. In the present paper, we investigate the presence of high-frequency plasma waves in the Martian plasma environment by making use of the high-resolution electric field data from the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft. Aims.This study aims to provide conclusive observational evidence of the occurrence of high-frequency plasma waves around the electron plasma frequency in the Martian magnetosphere. We observe two distinct wave modes with frequency below and above the electron plasma frequency. The characteristics of these high-frequency waves are quantified and presented here. We discuss the generation of possible wave modes by taking into account the ambient plasma parameters in the region of observation. Methods.We have made use of the medium frequency (100 Hz–32 kHz) burst mode-calibrated electric field data from the Langmuir Probe and Waves instrument on board NASA’s MAVEN mission. Due to the weak magnetic field strength, the electron gyro-frequency is much lower than the electron plasma frequency, which implies that the upper-hybrid and Langmuir waves have comparable frequencies. A total of 19 wave events with wave activities around electron plasma frequency were identified by examining high-resolution spectrograms of the electric field. Results.These waves were observed around 5 LT when MAVEN crossed the magnetopause boundary and entered the magnetosheath region. These waves are either a broadband- or narrowband-type with distinguishable features in the frequency domain. The narrowband-type waves have spectral peak above the electron plasma frequency. However, in the case of broadband-type waves, the spectral peak always occurred below the electron plasma frequency. The broadband waves consistently show a periodic modulation of 8–14 ms. Conclusions.The high-frequency narrowband-type waves observed above the electron plasma frequency are believed to be associated with upper-hybrid or Langmuir waves. However, the physical mechanism responsible for the generation of broadband-type waves and the associated 8–14 ms modulation remain unexplained and further investigation is required.

Astronomy & Astrophysics↗
DOE OSTI2016

Effects of electron pressure anisotropy on current sheet configuration

Recent spacecraft observations in the Earth's magnetosphere have demonstrated that the magnetotail current sheet can be supported by currents of anisotropic electron population. Strong electron currents are responsible for the formation of very thin (intense) current sheets playing the crucial role in stability of the Earth's magnetotail. We explore the properties of such thin current sheets with hot isotropic ions and cold anisotropic electrons. Decoupling of the motions of ions and electrons results in the generation of a polarization electric field. The distribution of the corresponding scalar potential is derived from the electron pressure balance and the quasi-neutrality condition. We find that electron pressure anisotropy is partially balanced by a field-aligned component of this polarization electric field. We propose a 2D model that describes a thin current sheet supported by currents of anisotropic electrons embedded in an ion-dominated current sheet. Current density profiles in our model agree well with THEMIS observations in the Earth's magnetotail.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Collisional and collisionless shocks

Shock waves are one of the most common plasma phenomena. They play a significant role in astrophysical and magnetospheric environments, as well as in laboratory plasmas. The paper focuses on two issues that underline important similarities and dissimilarities between collisional and collisionless shocks. The two types of shocks are similar in that they can be formed by the overtaking mechanism. We demonstrate that geometrical structures appearing early in the process of shock formation from the generic smooth initial state are quite universal and similar in both cases. Characterization of these structures (dubbed here the “mussel-shell”) is presented. Alongside with these similarities, there exist also significant differences between the two types of shocks. The classical collisional shocks usually connect two well-defined equilibrium states (those before and after the shock transition). Each of these equilibrium states is characterized by the thermodynamic parameters of density, temperature, and pressure whose upstream and downstream values are related by the continuity of mass, momentum, and energy flux. In the collisionless plasmas, however, this description does not work: the final state can be any of the much broader class of states constrained only by the requirement of being stable with respect to collisionless plasma instabilities. To find a final state (which does not have to be Maxwellian) one now has to follow the evolution of the system through the whole transition, and a lot of universality is lost. In some situations even the separation of scales between the global flow and shock transition may be lost. Taken together, these phenomena reveal a fascinating interplay of hydrodynamics, statistical mechanics, and plasma physics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Electrostatic upper-hybrid mode instability driven by a ring electron distribution

Quasi electrostatic fluctuations in the upper-hybrid frequency range are commonly detected in the planetary magnetospheric environment. The origin of such phenomena may relate to the instability driven by a loss-cone feature associated with the electrons populating the dipole-like magnetic field. The present paper carries out a one-dimensional electrostatic particle-in-cell simulation accompanied by a reduced quasilinear kinetic theoretical analysis to investigate the dynamics of the upper-hybrid mode instability driven by an initial ring electron distribution function, which is a form of loss-cone distribution. A favorable comparison is found between the two approaches, which shows that the reduced quasilinear theory, which is grounded in the concept of a model of the particle distribution function that is assumed to maintain a fixed mathematical form except that the macroscopic parameters that define the distribution are allowed to evolve in time, can be an effective tool in the study of plasma instabilities, especially if it is guided by and validated against the more rigorous simulation result.

Physics↗
DOE OSTI2011

Formation of high-{beta} plasma and stable confinement of toroidal electron plasma in Ring Trap 1

Formation of high-{beta} electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local {beta} value has exceeded 70%. Hot electrons are major component of electron populations, and its particle confinement time is 0.5 s. Plasma has a peaked density profile in strong field region [H. Saitoh et al., 23rd IAEA Fusion Energy Conference EXC/9-4Rb (2010)]. In pure electron plasma experiment, inward particle diffusion is realized, and electrons are stably trapped for more than 300 s. When the plasma is in turbulent state during beam injection, plasma flow has a shear, which activates the diocotron (Kelvin-Helmholtz) instability. The canonical angular momentum of the particle is not conserved in this phase, realizing the radial diffusion of charged particles across closed magnetic surfaces. [Z. Yoshida et al., Phys Rev. Lett. 104, 235004 (2010); H. Saitoh et al., Phys. Plasmas 17, 112111 (2010).].

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Wave processes during the interaction of the Earth’s magnetotail with dusty plasma near the lunar surface

The wave processes that take place under the interaction of the Earth’s magnetosphere with dusty plasma near the lunar surface are considered. It is shown that the waves can be excited for the photoelectron parameters corresponding to the quantum yield of the lunar regolith reported by Willis et al. [Photon and Particle Interactions with Surfaces in Space, Ed. by R. J. L. Grard (Reidel, Dordrecht, 1973), p. 389]. Ion-acoustic waves are excited in the regions of the transient magnetic and/or boundary magnetospheric layers due to the onset of linear hydrodynamic instability, whereas dust-acoustic waves are generated due to the onset of linear kinetic instability in the entire region of magnetotail interaction with dusty plasma near the Moon. In both cases, instability is caused by the relative motion of the magnetospheric ions and charged dust grains. The dynamics of the development of ion-acoustic and dust-acoustic turbulence is investigated. Ion-acoustic turbulence is described in terms of strong turbulence theory, while dust-acoustic turbulence is described in terms of weak turbulence theory. The energy density of oscillations, the effective collision frequencies, and the electric fields arising in the system are determined for both ion-acoustic and dust-acoustic turbulences. It is shown that the development of ion-acoustic turbulence in the dusty plasma system near the Moon can lead to the generation of electric fields that are somewhat weaker than those arising near the lunar surface due to the charging of the Moon’s surface under the action of solar radiation, but still sufficiently strong to affect the electric field pattern above the Moon. The obtained effective collision frequencies should be taken into consideration when deriving hydrodynamic equations for dusty plasma ions with allowance for turbulent plasma heating.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Inferring Magnetospheric Heavy Ion Density using EMIC Waves

We present a method to infer heavy ion concentration ratios from EMIC wave observations that result from ion-ion hybrid (IIH) resonance. A key feature of the ion-ion hybrid resonance is the concentration of wave energy in a field-aligned resonant mode that exhibits linear polarization. This mode converted wave is localized at the location where the frequency of a compressional wave driver matches the IIH resonance condition, which depends sensitively on the heavy ion concentration. This dependence makes it possible to estimate the heavy ion concentration ratio. In this letter, we evaluate the absorption coefficients at the IIH resonance at Earth's geosynchronous orbit for variable concentrations of He + and field-aligned wave numbers using a dipole magnetic field. Although wave absorption occurs for a wide range of heavy ion concentrations, it only occurs for a limited range of field-aligned wave numbers such that the IIH resonance frequency is close to, but not exactly the same as the crossover frequency. Using the wave absorption and observed EMIC waves from GOES-12 satellite, we demonstrate how this technique can be used to estimate that the He + concentration is around 4% near L = 6.6.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Effects of ion abundances on electromagnetic ion cyclotron wave growth rate in the vicinity of the plasmapause

Electromagnetic ion cyclotron (EMIC) waves in multi-ion species plasmas propagate in branches. Except for the branch corresponding to the heaviest ion species, which has only a resonance at its gyrofrequency, these branches are bounded below by a cutoff frequency and above by a resonant gyrofrequency. The condition for wave growth is determined by the thermal anisotropies of each ion species, j, which sets an upper bound, ω{sub j}{sup ∗}, on the wave frequency below which that ion species contributes positively to the growth rate. It follows that the relative positions of the cutoffs and the critical frequencies ω{sub j}{sup ∗} play a crucial role in determining whether a particular wave branch will be unstable. The effect of the magnetospheric ion abundances on the growth rate of each branch of the EMIC instability in a model where all the ion species have kappa velocity distributions is investigated by appealing to the above ideas. Using the variation of the cutoff frequencies predicted by cold plasma theory as a guide, optimal ion abundances that maximise the EMIC instability growth rate are sought. When the ring current is comprised predominantly of H{sup +} ions, all branches of the EMIC wave are destabilised, with the proton branch having the maximum growth rate. When the O{sup +} ion abundance in the ring current is increased, a decrease in the growth rate of the proton branch and cyclotron damping of the helium branch are observed. The oxygen branch, on the other hand, experiences an increase in the maximum growth rate with an increase in the O{sup +} ion abundance. When the ring current is comprised predominantly of He{sup +} ions, only the helium and oxygen branches of the EMIC wave are destabilised, with the helium branch having the maximum growth rate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Effects of pressure anisotropy on magnetospheric magnetohydrodynamics equilibrium of an internal ring current system

Effects of pressure anisotropy on magnetospheric magnetohydrodynamics equilibrium are studied analytically and numerically, where the plasma is confined by only poloidal magnetic field generated by an internal ring current. The plasma current due to finite pressure can be divided into two components; one remains at isotropic pressure and the other arises from pressure anisotropy. When p{sub ⊥}, the pressure perpendicular to the magnetic field, is larger than p{sub ∥}, the pressure parallel to the magnetic field, those two components of plasma current tend to cancel each other to reduce the total amount of plasma current. Equilibrium beta limit is also examined, where the beta is a ratio of the plasma pressure to the magnetic pressure. The equilibrium beta limit decreases as the pressure anisotropy becomes strong. The beta value is strictly limited by ellipticity of the equilibrium equation when p{sub ∥}>p{sub ⊥}. On the other hand, when p{sub ⊥}>p{sub ∥}, although the tendency of the beta limit agrees with the ellipticity condition of the equilibrium equation, equilibria with a hyperbolic region can be obtained by iterative procedure with practically reasonable convergence criteria.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Postmidnight depletion of the high-energy tail of the quiet plasmasphere

The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a Kp index of less than 3. We investigate the high energy range of the plasmasphere, which consists of ions at energies between 1-10 eV and contains approximately 5% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H + is depleted the most in the post-midnight sector (1-4 MLT), followed by O + and then He + . The relative depletion of each species across the post-midnight sector is not ordered by mass, which reveals ionospheric influence. We compare our results with keV energy electron data from HOPE and the Van Allen Probes Electric Fields and Waves (EFW) instrument spacecraft potential to rule out spacecraft charging. Our conclusion is that the post-midnight ion disappearance is due to diurnal ionospheric temperature variation and charge exchange processes

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Parameter spaces for linear and nonlinear whistler-mode waves

We examine the growth of magnetospheric whistler-mode waves which comprises a linear growth phase followed by a nonlinear growth phase. We construct time-profiles for the wave amplitude that smoothly match at the transition between linear and nonlinear wave growth. This matching procedure can only take place over a limited “matching region” in (N{sub h}/N{sub 0},A{sub T})-space, where A{sub T} is the electron thermal anisotropy, N{sub h} is the hot (energetic) electron number density, and N{sub 0} is the cold (background) electron number density. We construct this matching region and determine how the matching wave amplitude varies throughout the region. Further, we specify a boundary in (N{sub h}/N{sub 0},A{sub T})-space that separates a region where only linear chorus wave growth can occur from the region in which fully nonlinear chorus growth is possible. We expect that this boundary should prove of practical use in performing computationally expensive full-scale particle simulations, and in interpreting experimental wave data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Tethered Capacitor Charge Mitigation in Electron Beam Experiments

Energetic electron beams have been proposed for tracing magnetic field lines from the magnetosphere down to the ionosphere, in active experiments aimed at diagnosing mechanisms at play in the coupling between magnetosphere and ionosphere. It is recognized however that in the absence of an efficient mitigation technique, this approach would lead to unacceptably large spacecraft charging and positive potential buildup, which would result in environmental hazard for the spacecraft. This problem would be particularly acute in low density regions of the magnetosphere of interest in the study of magnetic field reconnection and substorm dynamics. A solution to this predicament could consist of creating a plasma contactor whereby a gas puff would be ionized, leading to the evacuation of positive charges and collection of cold electrons, thus compensating for the charges lost in the electron beam. A possible alternative is presented here, which consists of attaching a large passive conducting surface to the spacecraft, a “tethered capacitor”, from which negative charges would be drawn to compensate for those lost from the beam. This capacitor would then charge to a large positive potential, leaving the spacecraft and electron gun at a lower, acceptable positive potential. The tethered capacitor could have a relatively small mass; consisting only of a thin conducting surface that would be “inflated” as a result of repulsive electrostatic forces. This charge mitigation concept, as applied to active electron beam experiments, is explored using three dimensional particle-in-cell (PIC) simulations from which scaling laws can be inferred for the spacecraft and tethered capacitor potentials under proposed electron beam operations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Excitation of Banded Whistler Waves in the Magnetosphere

Banded whistler waves can be generated by the whistler anisotropy instability driven by two bi-Maxwellian electron components with T{sub {perpendicular}}/T{sub {parallel}} > 1 at different T{sub {parallel}} For typical magnetospheric condition of 1 < {omega}{sub e}/{Omega}{sub e} < 5 in regions associated with strong chorus, upper-band waves can be excited by anisotropic electrons below {approx} 1 keV, while lower-band waves are excited by anisotropic electrons above {approx} 10 keV. Lower-band waves are generally field-aligned and substantially electromagnetic, while upper-band waves propagate obliquely and have quasi-electrostatic fluctuating electric fields. The quasi-electrostatic feature of upper-band waves suggests that they may be more easily identified in electric field observations than in magnetic field observations. Upper-band waves are liable to Landau damping and the saturation level of upperband waves is lower than lower-band waves, consistent with observations that lower-band waves are stronger than upper-band waves on average. The oblique propagation, the lower saturation level, and the more severe Landau damping together would make upper-band waves more tightly confined to the geomagnetic equator (|{lambda}{sub m}| < {approx}10{sup o}) than lower-band waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

THE COUPLED PHYSICAL STRUCTURE OF GAS AND DUST IN THE IM Lup PROTOPLANETARY DISK

The spatial distribution of gas and solids in protoplanetary disks determines the composition and formation efficiency of planetary systems. A number of disks show starkly different distributions for the gas and small grains compared to millimeter–centimeter-sized dust. We present new Atacama Large Millimeter/Submillimeter Array observations of the dust continuum, CO, {sup 13}CO, and C{sup 18}O in the IM Lup protoplanetary disk, one of the first systems where this dust–gas dichotomy was clearly seen. The {sup 12}CO is detected out to a radius of 970 au, while the millimeter continuum emission is truncated at just 313 au. Based upon these data, we have built a comprehensive physical and chemical model for the disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. We constrain the distributions of gas and dust, the gas temperatures, the CO abundances, the CO optical depths, and the incident external radiation field. We find that the reduction/removal of dust from the outer disk exposes this region to higher stellar and external radiation and decreases the rate of freeze-out, allowing CO to remain in the gas out to large radial distances. We estimate a gas-phase CO abundance of 5% of the interstellar medium value and a low external radiation field ( G {sub 0} ≲ 4). The latter is consistent with that expected from the local stellar population. We additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A statistical study of three-second foreshock ULF waves observed by the Magnetospheric Multiscale mission

We perform a statistical study of 3-s ultra-low frequency (ULF) waves using Magnetospheric Multiscale observations in the Earth's foreshock region. The average phase velocity in the plasma rest frame is determined to be anti-sunward, and the intrinsic polarization is right-handed. We further examine the linear instability conditions based on the drift-bi-Maxwellian distribution functions according to the observed plasma conditions. The resulting instability is a solution to the common dispersion equation of the ion/ion right-hand non-resonant and left-hand resonant instabilities. The predicted wave propagation is also predominantly anti-sunward. The cyclotron resonant conditions of the solar wind and backstreaming beam ions are evaluated, and we find that, in some cases, the anti-sunward propagating waves can be resonant with beam ions, which was overlooked in previous studies. The study suggests that the dispersion equation provides the 3-s ULF waves a fundamental explanation that unifies a rich variety of resonant conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

3D magnetospheric parallel hybrid multi-grid method applied to planet–plasma interactions

We present a new method to exploit multiple refinement levels within a 3D parallel hybrid model, developed to study planet–plasma interactions. This model is based on the hybrid formalism: ions are kinetically treated whereas electrons are considered as a inertia-less fluid. Generally, ions are represented by numerical particles whose size equals the volume of the cells. Particles that leave a coarse grid subsequently entering a refined region are split into particles whose volume corresponds to the volume of the refined cells. The number of refined particles created from a coarse particle depends on the grid refinement rate. In order to conserve velocity distribution functions and to avoid calculations of average velocities, particles are not coalesced. Moreover, to ensure the constancy of particles' shape function sizes, the hybrid method is adapted to allow refined particles to move within a coarse region. Another innovation of this approach is the method developed to compute grid moments at interfaces between two refinement levels. Indeed, the hybrid method is adapted to accurately account for the special grid structure at the interfaces, avoiding any overlapping grid considerations. Some fundamental test runs were performed to validate our approach (e.g. quiet plasma flow, Alfven wave propagation). Lastly, we also show a planetary application of the model, simulating the interaction between Jupiter's moon Ganymede and the Jovian plasma.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

THE MAGNETOSPHERE OF THE ULTRACOOL DWARF DENIS 1048-3956

Ultracool dwarfs, the least-massive contributors to the stellar mass function, exhibit striking magnetic properties that are inconsistent with trends for more massive stars. Here, we present the widest-band radio observations to date of an ultracool dwarf, DENIS-P J104814.9-395604, in four 2 GHz bandwidths between wavelengths of 1 cm and 10 cm. These data were obtained with the Australia Telescope Compact Array using the new Compact Array Broadband Backend instrument. We detected a stable negatively sloped power-law spectrum in total intensity, with spectral index {alpha} = 1.71 {+-} 0.09. Circular polarization fractions between 0.25 and 0.4 were found at the low-frequency end of our detection band. We interpret these results as indicative of gyrosynchrotron emission. We suggest that the radio emission originates from beyond the corotation radius, R{sub C} , of the star. Adopting this model, we find R{sub C} between 1.2 R{sub *} and 2.9 R{sub *}, and a non-thermal electron density and magnetic field strength between 10{sup 5} and 10{sup 7.2} cm{sup -3} and between 70 and 260 G, respectively, at R{sub C} . The model accounts for the violation of the Guedel-Benz relation between X-ray and radio luminosities of low-mass stars by DENIS-P J104814.9-395604.

79 ASTRONOMY AND ASTROPHYSICS↗