Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “COSMIC”

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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Particle acceleration in cosmic plasmas; Proceedings of the Workshop, Bartol Research Inst., Newark, DE, Dec. 4-6, 1991

The present volume on particle acceleration in cosmic plasmas discusses transport theory, particle acceleration in the sun, heliosphere, and galaxy, particle acceleration at nonrelativistic shocks, and stochastic particle acceleration. Attention is given to particle acceleration in relativistic flows and shocks, simulations, composition and sources of high-energy cosmic rays, electron acceleration, and observation priorities and perspectives. Topics addressed include particle acceleration in the magnetosphere, particle transport from a turbulence perspective, numerical simulations of time-dependent cosmic ray mediated shocks, and solar flare plasma. Also discussed are relativistic shock waves and the excitation of plerions, ion acceleration at collisionless shock interactions, ultrahigh-energy cosmic rays from Fanaroff Riley, and constraints on electron acceleration in the Crab Nebula.

Zank, G. P.↗
NASA NTRS1993

Anuradha and low-energy cosmic rays

After critically reviewing observational results obtained by astronomical spacecraft in the interplanetary medium for several aspects of galactic cosmic rays (GCRs) and anomalous cosmic rays (ACRs), attention is given to spacecraft data gathered in the magnetosphere and a detailed description is given of the Anuradha cosmic-ray experiment carried by Spacelab-3. The Anuradha results discussed concern the orbit average flux and ionization state of ACRs, the origins of partially ionized galactic cosmic-ray sub-Fe and Fe ions, and the significance of enhanced abundance ratios of sub-Fe and Fe ions in GCRs inside the magnetosphere.

Biswas, S.↗
NASA NTRS1993

Alfven wave transport effects in the time evolution of parallel cosmic-ray-modified shocks

This paper presents a numerical study of the time evolution of plane, cosmic-ray modified shocks with magnetic field parallel to the shock normal, based on the diffusive shock acceleration formalism and including the effects from the finite propagation speed and energy of Alfven waves responsible for controlling the transport of the cosmic rays. The simulations discussed are based on a three-fluid model for the dynamics, but a more complete formalism is laid out for future work. The results of the simulations confirm earlier steady state analyses that found these Alfven transport effects to be potentially important when the upstream Alfven speed and the gas sound speed are comparable, i.e., when the plasma and magnetic pressures are similar. It is also clear, however, that the impact of Alfven transport effects, which tend to slow shock evolution and reduce the time asymptotic cosmic-ray pressure in the shock, is strongly dependent upon uncertain details in the transport models. Both cosmic-ray advection tied to streaming Alfven waves and dissipation of wave energy are important to include in the models. Further, Alfven transport properties on both sides of the shock are also influential.

Jones, T. W.↗
NASA NTRS1993

Cosmic ray decreases and particle acceleration in 1978-1982 and the associated solar wind structures

Results of a study of the time histories of particles in the energy range 1 MeV to 1 GeV at the times of greater than 3-percent cosmic ray decreases in the years 1978-1982 are presented. The intensity-time profiles of the particles are used to separate the cosmic ray decreases into four classes which are subsequently associated with three types of solar wind structures. Decreases in class 1 (15 events) and class 2 (26 events) are associated with shocks driven by energetic coronal mass ejections. For class 1 events, the ejecta are detected at 1 AU, whereas this is not usually the case for class 2 events. The shock must therefore play a dominant role in producing the cosmic ray depression in class 2 events. It is argued that since energetic particles (from MEV to GeV energies) seen at earth may respond to solar wind structures which are not detected at earth, consideration of particle observations over a wide range of energies is necessary for a full understanding of cosmic ray decreases.

Cane, H. V.↗
NASA NTRS1994

Cosmic ray models for early galactic lithium, beryllium, and boron production

To better understand the early galactic production of Li, Be, and B by cosmic ray spallation and fusion reactions, the dependence of these production rates on cosmic ray models and model parameters is examined. The sensitivity of elemental and isotropic production to the cosmic ray pathlength magnitude and energy dependence, source spectrum spallation kinematics, and cross section uncertainties is studied. Changes in these model features, particularly those features related to confinement, are shown to alter the Be- and B-versus-Fe slopes from a naive quadratic relation. The implications of our results for the diffuse gamma-ray background are examined, and the role of chemical evolution and its relation to our results is noted. It is also noted that the unmeasured high energy behavior of alpha + alpha fusion can lead to effects as large as a factor of 2 in the resultant yields. Future data should enable Population II Li, Be, and B abundances to constrain cosmic ray models for the early Galaxy.

Fields, Brian D.↗
NASA NTRS1994

Mass and radius of cosmic balloons

Cosmic balloons are spherical domain walls with relativistic particles trapped inside. We derive the exact mass and radius relations for a static cosmic balloon using Gauss-Codazzi equations. The cosmic balloon mass as a function of its radius, M(R), is found to have a functional form similar to that of fermion soliton stars, with a fixed point at 2GM(R)/R approximately or equal to 0.486 which corresponds to the limit of infinite central density. We derive a simple analytical approximation for the mass density of a spherically symmetric relativistic gas star. When applied to the computation of the mass and radius of a cosmic balloon, the analytical approximation yields fairly good agreement with the exact numerical solutions.

Wang, Yun↗
NASA NTRS1994

Stochastic reacceleration of cosmic rays in the interstellar medium

The effects of reacceleration on cosmic rays have been studied over a wide charge and energy range using a model of reacceleration by the interstellar turbulence. We take into account only inevitable stochastic reacceleration of cosmic rays by the random hydrodynamic waves, which supposedly exist in the interstellar medium and provide a means for cosmic-ray scattering and spatial diffusion in the Galaxy. Our calculations reproduce not only the B/C ratio but also the H and He data over the entire energy range where the measurements are available. However, the sub-Fe to Fe ratio is not fitted as well as the B/C ratio, and the reacceleration effect does not seem to remove the need for truncation of short path lengths, which is apparently required by the standard leaky box model. This work demonstrates that the cosmic-ray data can be represented at least as well by a reacceleration model with a simple rigidity power-law escape length, which agrees with the Kolmogorov-type spectrum of hydromagnetic turbulence, as they can by the standard leaky box model with its ad hoc escape lengths.

Seo, E. S.↗
NASA NTRS1994

The evolution of cosmic-ray-mediated magnetohydrodynamic shocks: A two-fluid approach

We study the shock structure and acceleration efficiency of cosmic-ray mediated Magnetohydrodynamic (MHD) shocks both analytically and numerically by using a two-fluid model. Our model includes the dynamical effect of magnetic fields and cosmic rays on a background thermal fluid. The steady state solution is derived by following the technique of Drury & Voelk (1981) and compared to numerical results. We explore the time evolution of plane-perpendicular, piston-driven shocks. From the results of analytical and numerical studies, we conclude that the mean magnetic field plays an important role in the structure and acceleration efficiency of cosmic-ray mediated MHD shocks. The acceleration of cosmic-ray particles becomes less efficient in the presence of strong magnetic pressure since the field makes the shock less compressive. This feature is more prominent at low Mach numbers than at high Mach numbers.

Jun, Byung-Il↗
NASA NTRS1994

Are cosmic rays effective for ionization of protoplanetary disks?

The principal uncertainty in studying the magnetic properties of protoplanetary disks concerns the ionization levels of the disk's gas. The low gas temperature precludes thermal ionization, leaving cosmic rays as the dominant source of ionization. It has been shown that the resulting electrical conductivity is just high enough for a MHD dynamo to produce contemporaneously a magnetic field in most of the extended parts of a turbulent protoplanetary disk. Here we argue that the effectiveness of cosmic rays to ionize the bulk of the gas is impaired by the influence of the generated magnetic field on the propagation of cosmic rays within a disk. Cosmic rays scatter on magnetic inhomogeneities, and, as a result, their penetration depth decreases to only a fraction of the disk half-thickness, resulting in a severe depletion of free charge from the midplane regions of a disk. That, in turn, undercuts the dynamo mechanism, so extended parts of the disk are free from a dynamically significant magnetic field. We also point out that any additional, even small, in situ source of ionization, such as radioactive Al-26, may again make a dynamo a viable regeneration process capable of producing a dynamically important magnetic field.

Dolginov, Arkady Z.↗
NASA NTRS1994

Time-dependent simulation of cosmic-ray shocks, including Alfven transport

Time evolution of plane, cosmic-ray modified shocks has been simulated numerically for the case with parallel magnetic fields. Computations were done in a 'three-fluid' dynamical model incorporating cosmic-ray and Alfven-wave energy transport equations. Nonlinear feedback from the cosmic rays and Alfven waves is included in the equation of motion for the underlying plasma, as is the finite propagation speed and energy dissipation of the Alfven waves. Exploratory results confirm earlier, steady state analyses that found these Alfven transport effects to be potentially important when the upstream Alfven speed and gas sound speeds are comparable. As noted earlier, Alfven transport effects tend to reduce the transfer of energy through a shock from gas to energetic particles. These studies show as well that the timescale for modification of the shock is altered in nonlinear ways. It is clear, however, that the consequences of Alfven transport are strongly model dependent and that both advection of cosmic rays by the waves and dissipation of wave energy in the plasma will be important to model correctly when quantitative results are needed. Comparison is made between simulations based on a constant diffusion coefficient and more realistic diffusion models allowing the diffusion coefficient to vary in response to changes in Alfven wave intensity. No really substantive differences were found between them.

Jones, T. W.↗
NASA NTRS1994

The cosmic-ray oxygen and helium spectra measured at Pioneer 10 over the time of the 1987 modulation minimum, and implications for the He/O source ratio

At the time of the recent sunspot minimum in 1987 when the cosmic-ray intensity within the heliosphere was a maximum, Pioneer 10(P10) was at a radial distance of approximately 42 AU. The solar modulation parameter Phi is estimated to have reached a minimum value of approximately 150 MV at P10 at that time, as compared with a minimum value of approximately 500 MV at the Earth. Thus P10 is in a sense effectively approximately 0.7 of the way to the heliospheric modulation boundary whatever its physical distance in astronomical units. Accordingly, the spectra of the various cosmic-ray species are much nearer to the interstellar spectra than any spectra ever before measured. We have therefore examined the penetrating high energy telescope (HET) data from P10 for a 2.5 yr period around 1987 to obtain a statistically accurate spectrum of oxygen nuclei over the energy range from 90 to 450 MeV/nucleon for comparison with a 'reference' interstellar spectrum. A similar spectrum is derived for helium nuclei. These two spectra and their ratios constitute important 'reference' spectra for all of the heavier cosmic-ray nuclei. The cosmic-ray source ratio required to explain the observed He/O ratio, when a full Galactic propagation calculation is carried out including secondary He-4 and He-3 production, is 15.9. The implications of this very low ratio and a comparison with the He/O ratio measured at high energies are discussed.

Webber, W. R.↗
NASA NTRS1994

Cosmic bullets as particle accelerators and radio sources

We have simulated in two dimensions the dynamical evolution of dense gas clouds(`cosmic bullets') moving supersonically through a uniform low-density medium. The diffusive shock acceleration of relativistic protons (cosmic rays) and their dynamical feedback on the background flow are included by the two-fluid model for this process. The acceleration of relativistic electrons is approximated by a test-particle model, and a passive magnetic field is followed by a simple advection scheme. Strong bow shocks, with Mach numbers similar to that of a bullet's motion, are the most important particle accelerators in the flow, while tail shocks and shocks inside the bullets do not play generally significant roles in this regard. For our simulation parameters, approximately greater than 10% of the initial bullet kinetic energy is converted to a combination of internal energy of gas and cosmic-ray protons by the time the bullets begin to be disrupted. Characteristically, the cosmic rays gain several percent of the available kinetic energy. Bullet destruction on timescales only a little larger than the ram pressure bullet crushing time begins in response to Kelvin-Helmholtz and especially to Rayleigh-Taylor instabilities along the forward bullet surface. For dense bullets this happens before the bullet is stopped by ram pressure. According to our simple model for synchrotron emission from relativistic electrons accelerated and transported within the flows, that emission increases rapidly as the bullet begins to fragment, when it is strongly dominated by field enhancement in sheared flows. Synchrotron emission from the acceleration region within the bow shock is, by contrast, much weaker.

Jones, T. W.↗
NASA NTRS1993

Large cosmic ray transient decreases observed in the heliosphere at the Earth, Voyagers 1 and 2 and Pioneer 10 from 1987 to 1991

Using the greater than 70-MeV cosmic ray rate data from the Interplanetary Monitoring Platform (IMP), Voyager, and Pioneer spacecraft, we have examined the role of large transient decreases in the overall cosmic ray decrease from 1987 to 1990. At least 12 separate transient decreases with magnitudes greater than 5% were observed at Voyager 2, which moved from a heliocentric radius of approximately 23 to 35 AU during the time period. Many, but not all, of these decreases were observed at IMP 8 near the Earth and at the Pioneer 10 between 42 and 54 AU near the ecliptic plane. However, only five of these decreases were observed at Voyager 1 at north heliographic latitude approximately 30 deg and radial distance between 32 and 46 AU. The period of decreasing cosmic ray intensity from 1987 to 1990 can be divided into two phases. During phase 1, between mid-1987 and early 1989, the average heliospheric current sheet tilt rapidly increased from approximately 8 deg to 65 deg as the solar activity was also increasing rapidly and the intensity at the Earth decreased by about 35%. Four large transient decreases were observed at the Earth during this time; however, transient decreases beyond the Earth were observed only near the ecliptic plane. In phase 2, from early 1989 to mid-1990 when the intensity at the Earth decreased by an additional approximately 60%, five large transient decreases were observed at all latitudes. During this time the current sheet tilt was always greater than 60 deg. Using a procedure to separate these large transient decreases from any possible slower long-term variations, we argue that these decreases appear to be responsible for much of the overall intensity decrease of 20 - 35% observed at all spacecraft near the equatorial plane in phase 1 as well as most of the larger intensity decrease of about 45 - 60% observed at all spacecraft during phase 2. The recovery of the cosmic ray intensity that started at the Earth in early 1990 moved outward in the heliosphere reaching the Voyager and Pioneer spacecraft about 6 months later. This is in contrast to what happened as the intensity began to recover was observed to begin almost simultaneously at all radii less than 25 AU. This difference suggests that during the current cycle, the mechanism responsible for the recovery must have propagated outward from the Sun. This could have been related to the reversal of the solar polar magnetic field which occurred in early 1990. The effects of large transients propagating outward in the heliosphere and becoming ineffective when they reach the heliospheric boundary could not have played a major role in the onset of the recovery in 1990, since in this case the recovery should have been observed first in the outer heliosphere.

Webber, W. R.↗
NASA NTRS1995

The faint limit of the Hubble Space Telescope faint object spectrograph and rejection of the cosmic-ray background

The faintest object which can be observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) is set by the detector cosmic-ray background and not by object flux. We use data from Beaver and Lyons to show that 48% of the background counts are from cosmic rays which each generate a near instantaneous burst of two or more counts. Setting the FOS threshold parameter REJLIM = 1, which rejects all frames with more than one count increases the ratio of signal-to-dark counts (S/D) by a factor of 1.94, regardless of the frame time or the object signal, because half of the dark counts which arrive in single counts (from either cosmic-ray bursts or thermal dark current photoemission) are rejected at the same rate as the object signal. But the signal-to-noise ratio (SNR proportional to S/square root of S + D) increases by at most a factor of 1.35, and for realistic parameters and taking into account dead time, we expect a gain in SNR of only 1.18. If a diode has failed and now emits noise, no data at all will be recorded. The chance of this occurring is approximately = 10% , and for this reason we do not recommend the use of REJLIM. The two-point correlation function of dark counts per pixel has strong peaks every four pixels, caused by the action of quarter-stepping on the counts from large bursts. The counts from such bursts spread over at least 80-100 diodes, and we show that such bursts can be rejected during data reduction if the data are recorded in RAPID mode with individual exposures of about 35 seconds. The SNR of the spectrum can also be improved by weighting each exposure by its SNR (a function ofthe mean dark count rate at that time), since dark varies by a factor of 2 around an orbit. These two procedures together increase the SNR by a factor of 1.1.3 (a 28% gain in exposure time) in regions of a spectrum where the object is much fainter than the background. We find that the Ly-alpha and O I sky emission lines give at most 4 (counts/array/s/sq arcsec), and typically half this number. With a small frame time and a small entrance aperture, these counts cause REJLIM = 1 to reject only a few percent of the data. We discuss only the HST FOS blue side detector, but the same ideas apply to any photon counter which records bursts of noise, and the calculations resemble those for the loss of signal due to coincidences in photon counters. In the ideal photon counter the dark counts are readily distinguished from photons. One way to do this is to add detectors which records only dark current, so that every cosmic ray produces more than one count and the instrument can be operated in an anti-coincidence mode.

Tytler, David↗
NASA NTRS1995

The influence of intermediate-scale variations in the heliospheric magnetic field on the transport of galactic cosmic rays

Variations in the heliospheric magnetic field occur on most scales including those lying intermediate between the gyro-radii of galactic cosmic rays and heliocentric radial distance. It is demonstrated that a correlation exists between these intermediate-scale variations in the magnetic field and the variations in the cosmic ray distribution function that result from the field variations. This correlation will affect the average transport of galactic cosmic rays by significantly altering the patterns of gradient and curvature drifts in the heliosphere. During the current solar cycle, the altered drift patterns can lead to larger radial gradients of the galactic cosmic rays and significantly smaller latitude gradients than is expected only from drifts in the mean magnetic field.

Fisk, L. A.↗
NASA NTRS1995

Cosmic-Ray Detectors With Interdigitated Electrodes

Detectors measure both positions of incidence and energies of incident charged particles. Stack of detector wafers intercept cosmic ray. Measure positions of incidence to determine cosmic-ray trajectory and charge generated within them (proportional to cosmic-ray energy dissipated within them). Interdigital electrode pattern repeated over many rows and columns on tops of detector wafers in stack. Electrode pattern defines pixels within which points of incidence of incident cosmic rays located.

Cunningham, Thomas J.↗
NASA NTRS1998

Cosmic Ray Energy Determination by the Reduced-Opening Angle Method

Accurate measurement of the primary galactic cosmic ray species energy dependence in the regime beyond approx. 500 GeV/a is difficult due to the low flux and the limitations of energy measurement techniques. However, such observations are essential to resolve several questions of current interest such as: Is the enrichment of heavy species (Z greater that or equal to 6) cosmic rays first reported at higher energies by the proton satellite' and then later at lower energies real? The results from a previous deployment of the reduced opening angle technique are inconclusive but the authors do point to limitations in the previous techniques. Another intriguing puzzle is the energy dependence of silicon cosmic rays. Two independent experiments using different experimental techniques indicate that silicon is under-abundant. At present the observation is limited by statistics; it could still be a three sigma fluctuation. However, if confirmed the current models of acceleration and propagation which are species independent are seriously inadequate. To progress further the species and energy dependence must be accurately measured in a manner that is free from systematic uncertainty. In this report we show that the reduced opening angle method offers a simple and relatively inexpensive method to answer these questions. First we present the physics of the reduced opening angle and indicate the expected energy and charge resolution. The proposed detector design is then presented followed by the expected performance. Where ever possible simple phenomenological expressions that allow 'back of the envelope' estimates are given. More details are presented in the appendices. The limit of the energy resolution and the expected event rates for iron cosmic rays are calculated. Salient points are summarized in the conclusions.

Smith, Arthur E.↗
NASA NTRS1997

A SPDS Node to Support the Systematic Interpretation of Cosmic Ray Data

The purpose of this project was to establish and maintain a Space Physics Data System (SPDS) node that supports the analysis and interpretation of current and future galactic cosmic ray (GCR) measurements by (1) providing on-line databases relevant to GCR propagation studies; (2) providing other on-line services, such as anonymous FTP access, mail list service and pointers to e-mail address books, to support the cosmic ray community; (3) providing a mechanism for those in the community who might wish to submit similar contributions for public access; (4) maintaining the node to assure that the databases remain current; and (5) investigating other possibilities, such as CD-ROM, for public dissemination of the data products. Shortly after the original grant to support these activities was established at Louisiana State University a detailed study of alternate choices for the node hardware was initiated. The chosen hardware was an Apple Workgroup Server 9150/120 consisting of a 120 MHz PowerPC 601 processor, 32 MB of memory, two I GB disks and one 2 GB disk. This hardware was ordered and installed and has been operating reliably ever since. A preliminary version of the database server was available during the first year effort and was used as part of the very successful SPDS demonstration during the Rome, Italy International Cosmic Ray Conference. For this server version we were able to establish the html and anonymous FTP server software, develop a Web page structure which can be easily modified to include new items, provide an on-line database of charge changing total cross sections, include the cross section prediction software of Silberberg & Tsao as well as Webber, Kish and Schrier for download access, and provide an on-line bibliography of the cross section measurement references by the Transport Collaboration. The preliminary version of this SPDS Cosmic Ray node was examined by members of the C&H SPDS committee and returned comments were used to refine the implementation.

Source record↗