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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Correlation of bow shock plasma wave turbulence with solar wind parameters

The rms field strengths of electrostatic and electromagnetic turbulence in the earth's bow shock, measured in the frequency range 20 Hz to 200 kHz with the Imp 6 satellite, are examined. The largest strengths of electrostatic turbulence occur when the upstream electron-to-proton temperature ratio is large and the proton temperature is small. No substantial correlation is found among the rms field strengths of electrostatic turbulence, the Alfven Mach number, the ratio of particle to magnetic-field pressure, and the shock normal angle. These results indicate that the strength of electrostatic turbulence in the bow shock is determined by the kinetic properties of the solar-wind plasma. The largest strengths for electromagnetic turbulence occur when the upstream particle density is large and when the shock normal angle is closer to 90 deg, supporting a previous conclusion that whistler waves comprise the electromagnetic turbulence in the bow shock.

Rodriguez, P.↗
NASA NTRS1975

Flux limit on cosmic ray acceleration by strong spherical pulsar waves

The study investigates the acceleration of cosmic rays by superrelativistic plasma waves. The pulsar wave field imposed upon the particles is that of a magnetic dipole wave including azimuthal dependence and near field terms. The refractive index of the plasma is assumed to be constant everywhere. Two distinct zones appear: in the near zone spherical effects dominate, particles may be decelerated; in the far zone the results for the motion differ noticeably from the vacuum case. From a WBK-like treatment for a spherical S wave, it is concluded that for a wave solution to be valid even near the light cylinder, the wave can carry a sufficiently small particle flux.

Asseo, E.↗
NASA NTRS1985

Wind Tunnel Seeding Systems for Laser Velocimeters

The principal motivating factor for convening the Workshop on the Development and Application of Wind Tunnel Seeding Systems for Laser Velocimeters is the necessity to achieve efficient operation and, most importantly, to insure accurate measurements with velocimeter techniques. The ultimate accuracy of particle scattering based laser velocimeter measurements of wind tunnel flow fields depends on the ability of the scattering particle to faithfully track the local flow field in which it is embedded. A complex relationship exists between the particle motion and the local flow field. This relationship is dependent on particle size, size distribution, shape, and density. To quantify the accuracy of the velocimeter measurements of the flow field, the researcher has to know the scattering particle characteristics. In order to obtain optimum velocimeter measurements, the researcher is striving to achieve control of the particle characteristics and to verify those characteristics at the measurement point. Additionally, the researcher is attempting to achieve maximum measurement efficiency through control of particle concentration and location in the flow field.

Hunter, W. W., Jr.↗
NASA NTRS1974

Cosmic ray scintillations. II - General theory of interplanetary scintillations

The motion of charged particles in a stochastic magnetic field with nonzero mean is considered via a generalized quasi-linear expansion of Liouville's equation. The general result is an equation relating cosmic ray scintillations to magnetic fluctuations and to cosmic ray gradients. The resonant interaction between particles and the random magnetic field is considered in detail, and the effect of nonlinear terms in the equations is considered. The nonlinear terms are important in damping out initial conditions and in determining conditions near cyclotron resonances. The application of the theory to the propagation of cosmic rays during quiet times in interplanetary space is considered. It is concluded that cosmic ray scintillations in interplanetary space may provide useful information about interplanetary particles and fields and also about nonlinear plasma interactions.

Owens, A. J.↗
NASA NTRS1972

The OPGT/MJS plasma wave science team

Some properties of a model magnetosphere for Saturn were studied in order to determine the bounds that can be set on surface field strength and trapped particle population. The primary observational constraint was that nonthermal radiation similar to the Jovian radio emissions must be undetectable from Earth. It is argued that for a Saturn surface field of approximately one gauss, particles that are energized as they diffuse in from the magnetopause with conservation of magnetic moment will produce synchrotron radiation levels that are undetectable at a range of 9.5 AU. The plasma instabilities that heat the oncoming wind particles at the bow shock and others that can limit the stably-trapped flux levels are also discussed.

Scarf, F. L.↗
NASA NTRS2015

Analytic Method to Estimate Particle Acceleration in Flux Ropes

The mechanism that accelerates particles to the energies required to produce the observed high-energy emission in solar flares is not well understood. Drake et al. (2006) proposed a kinetic mechanism for accelerating electrons in contracting magnetic islands formed by reconnection. In this model, particles that gyrate around magnetic field lines transit from island to island, increasing their energy by Fermi acceleration in those islands that are contracting. Based on these ideas, we present an analytic model to estimate the energy gain of particles orbiting around field lines inside a flux rope (2.5D magnetic island). We calculate the change in the velocity of the particles as the flux rope evolves in time. The method assumes a simple profile for the magnetic field of the evolving island; it can be applied to any case where flux ropes are formed. In our case, the flux-rope evolution is obtained from our recent high-resolution, compressible 2.5D MHD simulations of breakout eruptive flares. The simulations allow us to resolve in detail the generation and evolution of large-scale flux ropes as a result of sporadic and patchy reconnection in the flare current sheet. Our results show that the initial energy of particles can be increased by 2-5 times in a typical contracting island, before the island reconnects with the underlying arcade. Therefore, particles need to transit only from 3-7 islands to increase their energies by two orders of magnitude. These macroscopic regions, filled with a large number of particles, may explain the large observed rates of energetic electron production in flares. We conclude that this mechanism is a promising candidate for electron acceleration in flares, but further research is needed to extend our results to 3D flare conditions.

Energetic particle acceleration↗
NASA NTRS1965

Research within the ionosphere.

Satellite and rocket studies of neutral atmosphere and ionosphere with emphasis on charged particle motion in gravitational and electromagnetic fields

PARTICLE MOTION↗
NASA NTRS1967

Geomagnetic Euler potentials

Geomagnetic Euler potentials applied to conjugate points on earth surface and magnetosphere, and equations for drift shells traced by trapped particles

GEOMAGNETIC FIELD↗
NASA NTRS1969

Charged particles in the magnetosphere.

Charged particle population dynamics in outer radiation zone of magnetosphere, discussing ring current particles, protons, electrons, alpha particles and electric field

Van Allen, J. A.↗