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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 235 records · Page 13
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NASA NTRS1984

Observations of the dynamics of the cosmic ray modulation

New measurements of the outward propagation of the cosmic ray modulation and large transient decreases at a radial distance of 10-30 AU from the earth are reported. Also, new observations of the hysteresis effect in the 11-year modulation are presented for two solar cycles, and an attempt is made to reproduce the long-term modulation at earth from the observed transient or Forbush decreases. The results indicate that steady-state, spherically symmetric models of the heliosphere are not capable of explaining the 11-year variation. A time-dependent solution to the cosmic ray transport equation is required to describe the solar cosmic ray modulation.

Webber, W. R.↗
NASA NTRS2002

Propagation of Secondary Antiprotons and Cosmic Rays in the Galaxy

Recent more accurate antiproton data obtained by the BESS team during the last solar minimum pose a challenge to conventional propagation models of cosmic rays. In particular, the diffusive reacceleration model, which matches well key secondary/primary isotope ratios in cosmic rays, fails to reproduce the secondary antiproton spectrum. Tuning both secondary/primary isotope ratios and antiprotons is possible, but requires artificial breaks in the diffusion coefficient and the injection spectrum of primaries. We will discuss some possibilities to overcome these difficulties in the propagation models. We will present new results of our calculation of CR propagation in the Galaxy using the GALPROP code.

Moskalenko, I. V.↗
NASA NTRS1977

The age of the galactic cosmic rays derived from the abundance of Be-10

Satellite measurements of the abundance of the Be-10 isotope in galactic cosmic rays are used to determine the cosmic-ray lifetime for escape. The data are analyzed by employing a technique based on an extensive calibration of a cosmic-ray telescope with the aid of high-energy Be beams accelerated in a bevatron. It is found that the Be-10/Be abundance ratio at 80 MeV/nucleon is 0.028 + or - 0.104. A comparison of this result with calculations based on a homogeneous steady-state model of galactic cosmic-ray confinement and propagation yields an average interstellar density of 0.18 (+0.18, -0.11) atom/cu cm and a corresponding cosmic-ray lifetime of 17 (+24, -8) million years after solar modulation is taken into account. The low average density traversed by the cosmic rays is shown to suggest that the particles may be spending the major part of their existence in regions of very low matter density. The consequences of these results are discussed for models of cosmic-ray propagation in the Galaxy, including such alternatives as propagation in a galactic halo or in regions of interstellar space where the interstellar gas density is very low.

Garcia-Munoz, M.↗
NASA NTRS1972

The origin and propagation of VVH primary cosmic ray particles

Several source spectra were constructed from combinations of 4- and s-process nuclei to match the observed charge spectrum of VVH particles. Their propagation was then followed, allowing for interactions and decay, and comparisons were made between the calculated near-earth spectra and those observed during high altitude balloon flights. None of the models gave good agreement with observations.

Blanford, G. E., Jr.↗
NASA NTRS1985

Galactic propagation models consistent with the cosmic ray lifetime derived from Be-10 measurements

Using a propagation calculation with energy dependent parameters, including the depletion of short pathlengths, and incorporating experimental nuclear excitation functions, the variation of the Be-10/Be9 ratio with the matter densities in two nested confinement regions is investigated. It is shown that there is no unique correspondence between a Be-10/Be9 measurement at low energy and the density of matter in the galaxy. Be-10/Be9 measurements at both low and high energy are needed to fully specify the matter densities.

Guzik, T. G.↗
NASA NTRS1992

Cosmic ray albedo gamma rays from the quiet sun

We estimate the flux of gamma-rays that result from collisions of high energy galactic cosmic rays with the solar atmosphere. An important aspect of our model is the propagation of cosmic rays through the magnetic fields of the inner solar systems. We use diffusion to model propagation down to the bottom of the corona. Below the corona we trace particle orbits through the photospheric fields to determine the location of cosmic ray interactions in the solar atmosphere and evolve the resultant cascades. For our nominal choice of parameters, we predict an integrated flux of gamma rays (at 1 AU) of F(E(sub gamma) greater than 100 MeV) approximately = 5 x 10(exp -8)/sq cm sec. This can be an order of magnitude above the galactic background and should be observable by the Energetic Gamma Ray experiment telescope (EGRET).

Seckel, D.↗
NASA NTRS1974

The origin and propagation of VVH primary cosmic ray particles

In an attempt to match the observed charge spectrum of VVH particles, several source spectra have been constructed from combinations of r- and s-process nuclei. Their propagation has then been followed, allowing for interactions and decay, and comparisons have been made between the calculated near-earth spectra and those observed during high-altitude balloon flights. None of the models yet used leads to good agreement with observation, suggesting either that more complicated models need to be examined, or that different components (for instance the r- and s-process nuclei) have different histories.

Blanford, G. E., Jr.↗
NASA NTRS2012

Observation of an Anisotropy in the Galactic Cosmic Ray Arrival Direction at 400 TeV with IceCube

In this paper we report the first observation in the Southern hemisphere of an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This measurement was performed using cosmic ray induced muons recorded by the partially deployed IceCube observatory between May 2009 and May 2010. The data include a total of 33 x 10(exp 9) muon events with a median angular resolution of approx. 3 degrees. A sky map of the relative intensity in arrival direction over the Southern celestial sky is presented for cosmic ray median energies of 20 and 400 TeV. The same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV. Instead, the high energy skymap shows a different anisotropy structure including a deficit with a post-trial significance of -6.3 sigma. This anisotropy reveals a new feature of the Galactic cosmic ray distribution, which must be incorporated into theories of the origin and propagation of cosmic rays.

Abbasi, R.↗
NASA NTRS2011

Observation of Anisotropy in the Galactic Cosmic Ray Arrival Directions at 400 TEV With IceCube

In this paper we report the first observation in the Southern hemisphere of an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This measurement was performed using cosmic ray induced muons recorded by the partially deployed IceCube observatory between May 2009 and May 2010. The data include a total of 33x l0(epx 9) muon events with a median angular resolution of approx 3 degrees. A sky map of the relative intensity in arrival direction over the Southern celestial sky is presented for cosmic ray median energies of 20 and 400 Te V. The same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV. Instead, the high energy skymap shows a different anisotropy structure including a deficit with a post-trial significance of -6.30 sigma. This anisotropy reveals a new feature of the Galactic cosmic ray distribution, which must be incorporated into theories of the origin and propagation of cosmic rays.

Abbasi, R.↗
NASA NTRS1991

Viscosity and inertia in cosmic-ray transport - Effects of an average magnetic field

A generalized transport equation is introduced which describes the transport and propagation of cosmic rays in a magnetized, collisionless medium. The equation is valid if the cosmic-ray distribution function is nearly isotropic in momentum, if the ratio of fluid speed to fluid-flow particle speed is small, and if the ratio of collision time to time for change in the macroscopic flow is small. Five independent cosmic-ray viscosity coefficients are found, and the ralationship of this viscosity to particle orbits in a magnetic field is presented.

Williams, L. L.↗
NASA NTRS1986

Coronal and interplanetary propagation, interplanetary acceleration, cosmic-ray observations by deep space network and anomalous component

The purpose is to provide an overview of the contributions presented in sessions SH3, SH1.5, SH4.6 and SH4.7 of the 19th International Cosmic Ray Conference. These contributed papers indicate that steady progress continues to be made in both the observational and the theoretical aspects of the transport and acceleration of energetic charged particles in the heliosphere. Studies of solar and interplanetary particles have placed emphasis on particle directional distributions in relation to pitch-angle scattering and magnetic focusing, on the rigidity and spatial dependence of the mean free path, and on new propagation regimes in the inner and outer heliosphere. Coronal propagation appears in need of correlative multi-spacecraft studies in association with detailed observation of the flare process and coronal magnetic structures. Interplanetary acceleration has now gone into a consolidation phase, with theories being worked out in detail and checked against observation.

Ng, C. K.↗
NASA NTRS1995

Contact and pressure balance structures in two-fluid cosmic-ray hydrodynamics

The role of cosmic-ray-modified contact discontinuities and pressure balance structures in two-fluid cosmic-ray hydrodynamics in one Cartesian space dimension are investigated by means of analytic and numerical solution examples, as well as by weakly nonlinear asymptotics. The fundamental wave modes of the two-fluid cosmic-ray hydrodynamic equations in the long-wavelength limit consist of the backward and forward propagating cosmic-ray-modified sound waves, with sound speed dependent on both the cosmic-ray and thermal gas pressures; the contact discontinuity; and a pressure balance mode in which the sum ofthe cosmic ray and thermal gas pressure perturbations is zero. The pressure balance mode, like the contact discontinuity is advected with the background flow. The interaction of the pressure balance mode with the contact discontinuity is investigated by means of the method of multiple scales. The thermal gas and cosmic-ray pressure perturbations satisfy a linear diffusion equation, and entropy perturbations arising from nonisentropic initial conditions for the thermal gas are frozen into the fluid. The contact discontinuity and pressure balance eigenmodes both admit nonzero perturbations in the thermal gas, whereas the cosmic-ray-modified sound waves are isentropic. The total entropy perturbation is shared between the contact discontinuity and pressure balance eigenmodes, and examples are given in which there is a transfer of entropy between the two modes. In particular, N-wave type density disturbances are obtained which arise as a result of the entropy transfer between the two modes. A weakly nonlinear geometric optics perturbation expansion is used to study the long timescale evolution of the short-wavelength entropy wave and the thermal gas sound waves in a slowly varying, large-scale background flow. The weakly nonlinear geometric optics expansion is also used to generalize previous studies of squeezing instability for short-wavelength sound waves in the two fluid model, by including a weakly nonlinear wave steepening term that leads to shock formation, as well as the effect of long time and space dependence of the background flow. Implications of cosmic-ray-modified pressure balance structures and contact discontinuities in models of the interaction of traveling interplanetary shocks and compression and rarefraction waves with the solar wind termination shock are briefly discussed.

Webb, G. M.↗
NASA NTRS1971

Acceleration and propagation of high Z cosmic rays in a pulsar environment

The survival of high Z nuclei in the X-ray photon field of a pulsar is investigated. For heavy nuclei with energies greater than or equal to 100 GeV/nucleon, 100 keV X-ray photons have sufficient energy to cause photodisintegration with cross sections of approximately 10 to the minus 25th power sq cm. Using the observed properties of the Crab pulsar, extrapolation back to epochs when the pulsar was more active indicates that the photon field is sufficiently dense to prevent the acceleration of heavy nuclei within the velocity of light cylinder. On this model, the upper limit on the energy of the escaping nuclei varies with time. The models for cosmic ray acceleration in supernova explosions or by pulsars will be related to experimental observations.

Balasubrahmanyan, V. K.↗
NASA NTRS1971

The propagation of solar cosmic-ray bursts.

Description of a model showing analytically the three phases of anisotropy which occur during solar cosmic-ray events in the 7.5 to 21 MeV kinetic-energy interval and reported by McCracken et al. (1971): (1) a highly anisotropic, near field-aligned, initial phase, (2) a convective phase, and (3) a late-time phase in which the anisotropy is approximately perpendicular to the mean interplanetary magnetic field. The model is based on the cosmic-ray particles being convectively transported out from the sun, undergoing anisotropic diffusion along the interplanetary magnetic-field lines, and losing energy by adiabatic deceleration or by collision processes. The event is seen simply as a pulse moving outward from the sun after a cosmic-ray burst with a negative density-gradient in front of it and a positive gradient behind.

Ng, C. K.↗