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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Electron acceleration by Alfven waves in the magnetosphere

The self-consistent electron kinetics of Alfven waves on the electron inertial scale is studied using a 2D hybrid-kinetic description. The ions follow a fluid description for Alfven waves at frequencies below the ion cyclotron frequency. The parallel electron dynamics is treated kinetically using particle-in-cell techniques. In this model, the electron plasma mode is eliminated, and only the physics of the Alfven waves is retained. At sufficiently large amplitudes, it is found that oblique Alfven waves break due to finite electron inertia in a cold plasma. The consequence of wave breaking is the formation of an electron beam which can be unstable to the beam-plasma instability. The electrons supporting the parallel current thermalize into a non-Maxwellian distribution with an energetic tail up to several keV, assuming a reasonable magnetospheric Alfven speed. In hot plasma simulations, electron trapping is the principal mechanism of electron acceleration. It is proposed that wave breaking or electron trapping of oblique Alfven waves at 1 R(E) can result in electron acceleration and may explain some observed auroral phenomena.

Hui, C.-H.↗
NASA NTRS1989

Beam instability of the z mode in the solar wind

The instability of the slow extraordinary wave (z mode) caused by a tenuous population of energetic electrons, n(e), in the presence of a weak magnetic field and a cold plasma background, n(0), is investigated. The growth rate of the z mode was calculated within linear Vlasov theory and assuming that, for a weak magnetic field, the growth rate coincides with that of the electrostatic Langmuir wave, i.e., when the magnetic field is neglected for the cold background but retained for the energetic electrons. The analytical expression for the case of a thermal beam is deduced and numerically evaluated for some typical solar wind plasma conditions. The effects of the beam density, direction of propagation, and magnetic field on the observable polarization is discussed.

Krauss-Varban, D.↗
NASA NTRS1985

Variable frequency VLF signals in the magnetosphere Associated phenomena and plasma diagnostics

Coherent variable-frequency signals (ramps) extending from 1 to 8 kHz, injected into the magnetosphere from Siple Station, Antarctica (L=4.3), exhibit upper and lower cutoffs when received at the conjugate station, Roberval, Quebec. Ramp group delay measurements and ionospheric sounding data are used to determine the cold plasma density and L shell of the propagation path. Relationships among f, df/dt, and the 'phase equator' for gyroresonance are calculated using second-order resonance equations generalized to relativistic electrons. The concept thereby introduced is used to develop a diagnostic technique which, for an assumed g(alpha)(v exp -n) electron distribution, provides an estimate of the energy dependence n. Additional aspects of the magnetospheric response to ramp injection, such as emission triggering, curvature due to dispersion, and amplitude saturation, are discussed.

Carlson, C. R.↗
NASA NTRS2012

Radiation from Shock-Accelerated Particles

Plasma instabilities excited in collisionless shocks are responsible for particle acceleration, generation of magnetic fields , and associated radiation. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. The shock structure depends on the composition of the jet and ambient plasma (electron-positron or electron-ions). Strong electromagnetic fields are generated in the reverse , jet shock and provide an emission site. These magnetic fields contribute to the electron's transverse deflection behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. The detailed properties of the radiation are important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jet shocks, and supernova remnants

Nishikawa, Ken-ichi↗
NASA NTRS2000

Mini Magnetospheric Plasma Propulsion (M2P2)

The M2P2 concept is based on the transfer of momentum from the solar wind to an artificial magnetic field structure like that naturally occurs at all magnetized planets in the Solar System, called the magnetosphere. The objectives of this program include the following: (1) Demonstrate artificial magnetospheric inflation through cold plasma filling in vacuum; (2) Demonstrate deflection of a surrogate solar wind by an artificial magnetosphere in the laboratory vacuum chamber; (3) Compare theoretical calculations for thrust forces with laboratory measurements; (4) Develop flight control algorithms for planning mission specific trajectories; and (5) Develop M2P2 system concept.

Gallagher, Dennis↗
NASA NTRS1982

Magnetic field and plasma wave observations in a plasma cloud at Venus

Pioneer Venus magnetic field and plasma wave data are examined in a particularly clear example of a plasma cloud above the Venus ionosphere. The magnetic configuration is suggestive of acceleration of the plasma cloud by magnetic tension. If the plasma is at rest at the subsolar point, it could be accelerated to approximately 90 km/sec by the observed stress at the location of the measurement. This far exceeds the escape velocity and suggests that plasma clouds do form a significant loss mechanism for the Venus ionosphere but does not necessarily indicate that the plasma cloud is detached from the ionosphere proper. The plasma cloud is accompanied by strong plasma wave activity and is significantly hotter than the ionospheric plasma encountered later on the same pass. A loss rate of the order of 2 x 10 to the 25th ions/sec is estimated during this event. The geometry suggested by these observations is one of a ridge of dense cold plasma starting in the subsolar regions and flowing over the poles of the planet. Thus, these plasma clouds may be the planetary analog of cometary tail rays.

Russell, C. T.↗
NASA NTRS1988

Simulations of active ion injection experiments on ARCS 3

The ARCS 3 sounding rocket experiment used two argon guns oriented parallel and perpendicular to the geomagnetic field. The parameters of this experiment have been used in a series of particle simulations in order to interpret ion beam interaction with the multispecies ionospheric plasma. Along with the lower hybrid mode between the electron and the hydrogen gyrofrequencies, ion-ion hybrid modes between the hydrogen and helium gyrofrequencies and between the helium and oxygen gyrofrequencies are identified in the simulations. Besides these cold plasma modes, warm Bernstein modes of the respective ion species are identified. The parallel argon beam injections excite lower hybrid waves perpendicular to the magnetic field because of the finite thermal spread of the parallel beam. Perpendicular ion heating of background hydrogen, helium, and oxygen is comparable in the simulations. Comparisons are made with the wave and particle data from the ARCS 3 rocket experiment.

Hudson, M. K.↗
NASA NTRS1987

Nonlinear, relativistic Langmuir waves in astrophysical magnetospheres

Large amplitude, electrostatic plasma waves are relevant to physical processes occurring in the astrophysical magnetospheres wherein charged particles are accelerated to relativistic energies by strong waves emitted by pulsars, quasars, or radio galaxies. The nonlinear, relativistic theory of traveling Langmuir waves in a cold plasma is reviewed. The cases of streaming electron plasma, electronic plasma, and two-streams are discussed.

Chian, Abraham C.-L.↗
NASA NTRS2021

Core-Plasma Refilling and Erosion: Science Justification

Global magnetospheric models do not currently couple dynamic plasmaspheric plasma due to computational limitations that will be overcome by 2050. A true GGCM will need to include a dynamic plasmasphere for both physics and space weather prediction. Such inclusion requires that we answer longstanding, fundamental questions about the life cycle of core (<10 eV, plasmaspheric) plasma: how it gets into the inner magnetosphere, and how it is eroded. Erosion and refilling are processes controlling a fundamental space plasma population. During every geomagnetic disturbance, tens of metric tons of plasma are rapidly eroded away, then slowly and unevenly replenished. After several decades we still do not understand the cross-scale mechanisms proposed to be responsible for these 2 processes. Removal and replacement of this enormous plasma mass is as important to the dynamics of the magnetosphere as solar-wind driving. Our community must dedicate the resources and effort needed to solve this enduring puzzle. Other white papers submitted in response to the HP2050 call are discussing cold plasma and ionospheric outflow in more general contexts. This white paper deals specifically with the science justification for studying refilling and erosion.

Plasmasphere, core-plasma, erosion, refilling↗
NASA NTRS1984

Correlation of auroral hiss and upward electron beams near the polar cusp

Data were obtained from the DE-1 high-altitude plasma instrument (HAPI) and plasma wave instrument (PWI) during outbound passes through the polar cusp near local noon. The observed distribution functions of electron beams are fitted by drifting Maxwellian functions and the observed distribution functions of hot background electrons by isotropic Maxwellian functions. In addition, the cold plasma density is inferred from knowledge of the electron plasma frequency and the measured density of the warm plasma, including the electron beam distribution. The empirically fitted plasma parameters, including density, temperature and drifting energy, are used to solve the linear dispersion equation for the resulting whistler mode emissions. Because the whistler mode becomes quasi-electrostatic for wave-normal angles near the resonance cone, the electrostatic approximation is used for the whistler mode dispersion relation. The results of wave instability analyses are then compared with the wave observations. A ray tracing of cusp hiss emission is conducted to locate the wave source region (at about one earth-radius).

Lin, C. S.↗
NASA NTRS2005

Interstellar PAH in the Laboratory and in Space. What have we Learned from the New Generation of Laboratory and Observational Studies?

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-UV and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20 cm(sup -1)) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10 cm(sup -1)). The laboratory data are discussed and compared with recent astronomical spectra of large and narrow DIBs and with the spectra of circumstellar environments of selected carbon stars and the implications for the interstellar PAH population are derived. Preliminary results also show that carbon nanoparticles are formed during the short residence time of the precursors in the plasma.

Salama, Farid↗
NASA NTRS1987

Polarization of low-frequency electromagnetic radiation in the lobes of Jupiter's magnetotail

The plasma wave instruments on the Voyager spacecraft have detected intense electromagnetic radiation within the lobes of Jupiter's magnetic tail down to the lowest frequency of the detector (10 Hz). During a yaw maneuver performed by Voyager 1 in the lobe of the Jovian magnetotail, a modulation appeared in the amplitudes of waves detected in the 10-, 17.8- and 31.1-Hz channels of the plasma wave analyzer, well below the local electron cyclotron frequency of 260 Hz. The lowest amplitudes occurred when the antenna axis was most nearly parallel to the magnetic field. Wave amplitudes in the 56.2-Hz and higher frequency channels remained nearly constant during the maneuver. From the cold-plasma theory of electromagnetic waves, it is concluded that the plasma frequency was between the 56.2- and 31.1-Hz channels where the parallel-polarized component of the spectrum cuts off. This implies a tail-lobe density between 0.000032 and 0.000015/cu cm. The left-hand cutoff frequency would then be below 10 Hz, consistent with either the Z-mode (L, X) or whistlers (R-mode) in the modulated channels.

Moses, S. L.↗
NASA NTRS1986

Electron-cyclotron maser instability in relativistic plasmas

The electron-cyclotron maser instability is studied for the case of an anisotropic electron velocity distribution in the regime where the relativistic corrections to the wave dispersion are significant. Solution of the linear dispersion relation reveals that when the plasma frequency-gyrofrequency ratio is less than v(te)/c, the instability is localized just below k(perpendicular)c/Omega(e) = 1. The growth rate is then strongly peaked for emission at 90 deg to the magnetic field and is considerably larger than would be the case if the cold-plasma dispersion theory were valid. These features are confirmed by EM particle simulations.

Pritchett, P. L.↗
NASA NTRS2005

Spectroscopy of Jet-Cooled Neutral and Ionized PAHs: Implications for Interstellar Dust

We present the gas-phase spectroscopy of neutral and ionized polycyclic aromatic hydrocarbons (PAHs) measured in the W-Visible-NIR range in an astrophysically relevant environment. These measurements provide data on PAHs and nanometer sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laborat'ory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature ($\sim lOO$-K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS) and multiplex integrated cavity output spectroscopy (MICOS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. The electronic bands measured for ionized PAH are found to be intrinsically broad ($\geq$20 cm$^{-l}$) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10 cm$^{-l}$). The laboratory data are discussed and compared with recent astronomical spectra of large and narrow DIBs and with the spectra of circumstellar environments of selected carbon stars (see contribution of Cami et al.) and the implications for the interstellar PAH population are derived. Preliminary results also show that carbon nanoparticles are formed during the short residence time of the precursors in the plasma. This finding holds great potential for understanding the formation process of interstellar grains.

Salama, F.↗
NASA NTRS2005

PAHs and the Diffuse Interstellar Bands. What have we Learned from the New Generation of Laboratory and Observational Studies?

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones, An extensive laboratory program has been developed at NASA Ames to characterize the physical and chemical properties of PAHs in astrophysical environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-W and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong V W radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high- sensitivity spectroscopy and directly compared to the astronomical data. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20/cm) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10/cm).

Salama, Farid↗
NASA NTRS2006

Astrochemistry: Recent Advances in the Study of Carbon Molecules in Space

Carbon molecules and ions play an important role in space. Polycyclic Aromatic Hydrocarbons (PAHs) are the best-known candidates to account for the infrared emission bands (UIR bands) and PAH spectral features are now being used as probes of the interstellar medium in Galactic and extra-galactic environments. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory Astrochemistry is to reproduce (in a realistic way) the physical conditions that exist in the emission and absorption interstellar zones. An extensive laboratory program has been developed in various laboratories to characterize the physical and chemical properties of PAHs in astrophysical environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. The harsh physical conditions of the interstellar medium - characterized by a low temperature, an absence of collisions and strong ultraviolet radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase.

Salama, Farid↗
NASA NTRS1989

Space plasma contractor research, 1988

Results of experiments conducted on hollow cathode-based plasma contractors are reported. Specific tests in which attempts were made to vary plasma conditions in the simulated ionospheric plasma are described. Experimental results showing the effects of contractor flowrate and ion collecting surface size on contactor performance and contactor plasma plume geometry are presented. In addition to this work, one-dimensional solutions to spherical and cylindircal space-charge limited double-sheath problems are developed. A technique is proposed that can be used to apply these solutions to the problem of current flow through elongated double-sheaths that separate two cold plasmas. Two conference papers which describe the essential features of the plasma contacting process and present data that should facilitate calibration of comprehensive numerical models of the plasma contacting process are also included.

Williams, John D.↗
NASA NTRS1978

A multiple-scattering approach to transient electromagnetic interaction with plasmas

A multiple-scattering method is described which is applicable to the transient plasma problem concerning the interaction between transient electromagnetic waves and plasmas. The method starts with the time-dependent wave fields scattered by a linear electric dipole when illuminated by a transient plane wave. It avoids the use of Fourier transform methods and provides additional physical insight into the origin of the frequency-dispersive properties of material media. The results are applicable only to cold plasmas since spatial dispersion is neglected, implying that effects due to thermal velocities of electrons - such as incoherent scatter - are not covered by the theory. The advantages of the method for initiation of the student into transient electromagnetics in dispersive media are identified as conceptual simplicity and computational simplicity. The entire analysis is in the time domain.

Bowhill, S. A.↗