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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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NASA NTRS1985

Possible origin of the anomalous component of cosmic rays

The possible origin of the anomalous cosmic rays (ACR) are studied in terms of stellar wind injection from O type stars and their acceleration in shock fronts of SNR's. It is assumed that a fraction of heavy ions will encounter interstellar shock fronts of SNR's and these are accelerated to about 5 to 100 MeV/N and give rise to ACR's. Typically these ions would travel a distance of the order of a few 1000 pc. Therefore it is estimated that O type stars in a volume of radius of a few Kpc around the solar system are contributing to the intensity of ACR in the local ISM. From observational data, the intensity of ACR in the local ISM is estimated. It is suggested that these ACR ions enter the solar system along the solar dipole field lines connected to the interplanetary magnetic field lines.

Biswas, S.↗
NASA NTRS1984

Transient behavior of flare-associated solar wind. II - Gas dynamics in a nonradial open field region

Transient behavior of flare-associated solar wind in the nonradial open field region is numerically investigated, taking into account the thermal and dynamical coupling between the chromosphere and the corona. A realistic steady solar wind is constructed which passes through the inner X-type critical point in the rapidly diverging region. The wind speed shows a local maximum at the middle, O-type, critical point. The wind's density and pressure distributions decrease abruptly in the rapidly diverging region of the flow tube. The transient behavior of the wind following flare energy deposition includes ascending and descending conduction fronts. Thermal instability occurs in the lower corona, and ascending material flows out through the throat after the flare energy input ceases. A local density distribution peak is generated at the shock front due to the pressure deficit just behind the shock front.

Nagai, F.↗
NASA NTRS1994

Relativistic particle acceleration in plerions

We discuss recent research on the structure and particle acceleration properties of relativistic shock waves in which the magnetic field is transverse to the flow direction in the upstream medium, and whose composition is either pure electrons and positrons or primarily electrons and positrons with an admixture of heavy ions. Particle-in-cell simulation techniques as well as analytic theory have been used to show that such shocks in pure pair plasmas are fully thermalized -- the downstream particle spectra are relativistic Maxwellians at the temperature expected from the jump conditions. On the other hand, shocks containing heavy ions which are a minority constituent by number but which carry most of the energy density in the upstream medium do put approximately 20% of the flow energy into a nonthermal population of pairs downstream, whose distribution in energy space is N(E) varies as E(exp -2), where N(E)dE is the number of particles with energy between E and E+dE. The mechanism of thermalization and particle acceleration is found to be synchrotron maser activity in the shock front, stimulated by the quasi-coherent gyration of the whole particle population as the plasma flowing into the shock reflects from the magnetic field in the shock front. The synchrotron maser modes radiated by the heavy ions are absorbed by the pairs at their (relativistic) cyclotron frequencies, allowing the maximum energy achievable by the pairs to be gamma(sub +/-)m(sub +/-)c squared = m(sub i)c squared gamma(sub 1)/Z(sub i), where gamma(sub 1) is the Lorentz factor of the upstream flow and Z(sub i) is the atomic number of the ions. The shock's spatial structure is shown to contain a series of 'overshoots' in the magnetic field, regions where the gyrating heavy ions compress the magnetic field to levels in excess of the eventual downstream value. This shock model is applied to an interpretation of the structure of the inner regions of the Crab Nebula, in particular to the 'wisps,' surface brightness enhancements near the pulsar. We argue that these surface brightness enhancements are the regions of magnetic overshoot, which appear brighter because the small Larmor radius pairs are compressed and radiate more efficiently in the regions of more intense magnetic field. This interpretation suggests that the structure of the shock terminating the pulsar's wind in the Crab Nebula is spatially resolved, and allows one to measure gamma(sub 1) and a number of other properties of the pulsar's wind. We also discuss applications of the shock theory to the termination shocks of the winds from rotation-powered pulsars embedded in compact binaries. We show that this model adequately accounts for (and indeed predicted) the recently discovered X-ray flux from PSR 1957+20, and we discuss several other applications to other examples of these systems.

Arons, Jonathan↗
NASA NTRS1947

Analytical Treatment of Normal Condensation Shock

The condensation of water vapor in an air consequences: acquisition of heat (liberated heat vaporization; loss of mass on the part of the flowing gas (water vapor is converted to liquid); change in the specific gas constants and of the ratio k of the specific heats (caused by change of gas composition). A discontinuous change of state is therefore connected with the condensation; schlieren photographs of supersonic flows in two-dimensional Laval nozzles show two intersecting oblique shock fronts that in the case of high humidities may merge near the point of intersection into one normal shock front.

Heybey↗
NASA NTRS2019

Understanding the Role of 𝛼 Particles in Oblique Heliospheric Shock Oscillations

Recent observations by DSCOVR provide high temporal resolution (50 samples per second) magnetic vector field data that allows investigating the details of oblique heliospheric shock oscillations. It was found that some of these shocks exhibit magnetic oscillations, both downstream and upstream of the shock front. The DSCOVR/MAG magnetic field data are supplemented by an extensive database of low Mach number (M < 3) low‐β (<1) shock data observed by Wind albeit with lower temporal resolution. Motivated by the observations, we use the 2.5D hybrid model of the oblique shocks with α particles in addition to kinetic protons and electron fluid. We model the properties of the oblique shocks for a number of typical parameters found in observations and study the effects of the shock parameters and the relative α particle abundances on the properties of the shock magnetic field, density, and velocity oscillations. We find the α particles “surf” on the shock front and produce a wake of density oscillations. We examine the details of the phase space of the ions as well as the ion velocity distribution functions in various parts of the shock and study their nonthermal properties. We determine the effects of the α particle kinetic properties and abundances on the structure and dynamics of the shock downstream oscillations for a range of parameters relevant to low Mach number low‐β heliospheric shocks.

Ofman, L.↗
NASA NTRS1979

Acceleration of energetic protons by interplanetary shocks

The University of Iowa instrument aboard Pioneer 11 detected 69 energetic proton events (EPE) (in the 0.6-3.4 MeV energy range) during 1973-1974 in the heliocentric radial range 1-5 AU. Sixty percent of the EPE peak within plus or minus 5 hours of a corotating interaction region (CIR) boundary, while 19% peak inside and 21% peak outside the interaction regions. Of the CIR boundaries at which an EPE peaks with plus or minus 5 hours, 80% have associated shocks. The observed intensities and pitch angle distributions of protons near shock fronts are consistent with a theoretical simulation of the acceleration of protons by a drift in the electric field at the shock front.

Pesses, M. E.↗
NASA NTRS1973

Pioneer 8 observations and interpretations of sixteen interplanetary shock waves observed in 1968.

A study has been made of 16 interplanetary shock waves observed in 1968 by Pioneer 8 at large distances from earth. A comparison with the shapes of interplanetary shock fronts obtained by De Young and Hundhausen (1971) suggests that in general the ejection of flare gas occurs within a cone of half-angle between 30 and 60 deg. For near-earth events a deflection of the shock front has been observed, possibly owing to an interaction with the bow shock. The average duration of the postshock perturbation is about 20 hours. Strong magnetic fields and rapid fluctuations occur during the first 6 to 12 hours. Electric field perturbations in the VLF band are also noted during these periods. There is limited evidence for one corotating shock in these data.

Bavassano, B.↗
NASA NTRS1975

On the possibility of detecting solar flare effects in the zodiacal light

To evaluate possible effects of solar flares on the brightness of the inner zodiacal light, it is necessary to consider the brightness contribution along the line of sight and as a function of sun-particle distance. For this purpose, models of the brightness contribution along the line of sight are presented for both dielectric and metallic particles with a spatial distribution of the form 1, 1/r, and 1/r-squared. These models are discussed in terms of the geometry of shock front interaction. A reported zodiacal light enhancement following a solar flare (Blackwell and Ingham, 1961) is analyzed on the basis of the shock front geometry.

Misconi, N. Y.↗
NASA NTRS1982

Motions of the cloud medium behind large scale galactic shocks

Mechanisms of decelerating the cloud medium in the large-scale galactic shock are studied. It is shown that the process of cloud-cloud collisions, which results in diffusive momentum transport and hence gives rise to the turbulent viscosity, is very effective in slowing down the cloud medium so that the postshock velocity of the intercloud medium can be matched within a short distance behind the shock front. The drag force exerted by the slow-moving intercloud medium alone is simply not enough to effectively decelerate the cloud medium in the shock. By the use of the results of Shu et al (1972), the internal structure of the shock of the cloud medium is analyzed by including turbulent viscous effects. The thickness of the shock is found to be on the order of 100 pc if the turbulent viscosity is taken proportional to the mean free path of the cloud-cloud collisions. The phase transition takes place in an even thinner layer on the order of 10 pc immediately after the viscous shock front of the intercloud medium.

Yuan, C.↗
NASA NTRS1974

Post-shock spikes: A new feature of proton and alpha enhancements associated with an interplanetary shock wave

Abrupt and prolonged enhancements in the intensities of 100 to approximately 2000 keV nucleon protons and alpha particles observed in interplanetary space are interpreted as particle populations confined between an interplanetary shock front and a magnetic field discontinuity. Prominent intensity spikes observed only below approximately 400 keV per charge for both protons and alpha particles several hours behind the shock front suggest that some fraction of the confined particles is accelerated by an energy per charge dependent process.

Gloeckler, G.↗
NASA NTRS1990

Supernovae and supernova remnants at low frequencies

The importance of low-frequency observations of the intrinsic radio emission from supernovae and their remnants is discussed, with special attention given to an example of a peculiarity at low frequencies of the 38-MHz 'flare' observed from Cas A in the mid-1970s. It is suggested that, for explosions from supernovae in a low-density wind, it may be possible to follow the absorption over a large range of shock front radii. Absorption local to the remnants can occur in H II regions created by the supernovae or their progenitors and in the cooling layers of radiative shock fronts, or in the ionized interstellar medium. Observations of emission as well as of absorption are necessary to determine the location of the ionized gas.

Chevalier, Roger A.↗
NASA NTRSDate not supplied

MARS 2020 Backshell Radiative Heating Measurement and Shock Tube Verification

In February 2021, the Perseverance rover was brought to the surface of Mars by the Mars 2020 mission. A feature of the Mars 2020 capsule was instrumentation to measure its entry, descent and landing (EDL) with the so-called Mars EDL Instrumentation 2 (MEDLI2) [1]. The MEDLI2 introduced, among other things, backshell instrumentation, including a broadband radiometer. The radiometer was mounted on the leeside of the vehicle next to thermocouple plugs and a heat flux gauge. The data returned by the leeside MEDLI2 heat flux gauge is largely analogous to that measured by the COMARS gauge flown on the ExoMars Schiaparelli [2] entry in that it is measuring heat flux in an area that is entirely dominated by radiative heating. The COMARS measurement provided excellent validation of backshell radiative heating models for Mars entry, albeit at a limited number of points [3]. The MEDLI2 heat flux gauge measurement effectively confirmed the quality of the prediction, extended over the full trajectory, as will be presented in this paper. The MEDLI2 radiometer,however, was blocked by ablation products and suffered a loss of half of its signal. The second backshell heat flux gauge installed on the windside of the vehicle was also well predicted, although the heating had both radiative and convective contributions. It was desired to reproduce the conditions of the Mars 2020 entry via ground testing in the Electric Arc Shock Tube (EAST) at NASA Ames. Tests to verify stagnation line heating were previously reported in EAST, confirming the presence of shock layer radiation as the major discrepancy in heatshield temperature modelling [4]. Therefore, tests for stagnation line heating were not repeated. Instead, the shock tube informed bias method [5, 6] was used to identify test conditions that may produce similarity to streamlines that pass around the backside of the vehicle and are responsible for the radiation observed at the two heat flux gauge locations. This method was used to identify a range of velocities and densities in the shock tube that are relevant for confirming the radiative environment encountered. This paper reports the results obtained in the 10 cm diameter EAST shock tube, corresponding to later trajectory points at ambient pressures of 1.1-2.0 Torr and velocities from 1.2-3.5 km/s. The test series employed two primary diagnostics: emission spectroscopy and tunable diode laser absorption spectroscopy (TDLAS). The emission spectroscopy performed broadband measurements of the radiative emission of the 4.3 and 2.7 m bands of CO2 at flight similar conditions, obtaining both spectral and spatial data corresponding to the relaxation behind the shock front. The TDLAS measured the absorption of several lines of CO and CO2 and obtains species number densities and temperatures as a function of time behind the shock front. This paper will review highlights of this test series and analyses of the emission and absorption data. While the datasets generally show good agreement with predictions, a few discrepancies and items for additional investigation are identified and will be discussed

Brett A Cruden↗
NASA NTRS1993

Near-specular reflection of ions at quasi-parallel shocks

One-dimensional hybrid simulations and a semianalytical model of the shock front are employed to investigate the source regions in the incident ion phase space of reflected and transmitted ions, the relative importance of the electric and magnetic forces in the reflection of incident ions, and how these characteristics change in time. The phase space origin of reflected particles and the fraction of incident ions that reflect are found to depend on the electromagnetic field structure of the shock front at the time the ions encounter it. The reflection fraction is maximized when the electric field along the shock normal (Ex) and the noncoplanar magnetic field (By) are at their maximum values. When Ex and By are large, the reflection process produces a beam that is cooler, more dense, and closer to specular than when they are small.

Mckean, M. E.↗
NASA NTRS1978

The structure and spectrum of a colliding-cloud system and its possible relationship to QSOs

A collision between two gas clouds with initial densities of approximately 10 million per cu cm, velocities of about 1000 km/s, and radii of approximately 1 pc is investigated quantitatively by coupling a calculation of the radiation spectrum resulting from the anticipated shock fronts with a computation for the conversion of this high-energy radiation into optical emission in adjacent photoionized regions. The detailed structure of the colliding clouds is discussed, and the effects of an ambient magnetic field are considered. The combined emission-line spectrum is presented along with continuum emission estimates for thermal, synchrotron, and very-high-energy bremsstrahlung mechanisms. It is shown that significant continua can be produced over the range from 300 microns to 3 keV, including a blackbody contribution from a high-density neutral region between the shock fronts, free-free and free-bound radiation from the cooling zones directly behind the shocks, and free-free, free-bound, and two-photon radiation from the photoionized regions immediately ahead of and behind the cooling zones. The theoretical spectrum of the structure resulting from the collision is found to be similar in general and in some details to those observed for typical quasars.

Daltabuit, E.↗
NASA NTRS2014

MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows

Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.

Sun: chromosphere↗
NASA NTRS1987

A sheet description of the emission from middle-aged supernova remnants

The hypothesis that sheetlike shock fronts propagating into large clouds immersed in a fairly uniform intercloud medium can provide a consistent picture accounting for essentially all the observational data for the Cygnus Loop SNR is considered. Filaments are interpreted as line-of-sight projections of portions of the sheet. Variations in the projection of the shock velocity along the line of sight lead naturally to 'turbulent' velocities consistent with observation. An analog model of a large, distorted, bumpy shock front is presented and shown to produce the observed morphology of the remnant's prominent optical filaments. Comparison with the observed morphology supports the idea that regions of optical emission lie on the local outer boundary of the shell and have not been engulfed by the blast wave. Bright X-ray emission arises when the blast wave encounters a preshock medium with an intermediate density higher than average for the adiabatic portion of the remnant, but still lower than that required for the shock to become radiative.

Hester, J. Jeff↗
NASA NTRS1979

Some recent coronal line observations of supernova remnants

Observations of optical coronal lines from the supernova remnants Puppis A and N 49 in the Large Magellanic Cloud carried out at Cerro Tololo and the Anglo-Australian Observatory are reported. The eastern section of Puppis A was searched for forbidden Fe X and Fe XIV emissions in order to confirm the previous detection of a lower temperature component of the X-ray source. Strong forbidden Fe XIV emission was detected in one region consistent with the position of the previously observed soft X-ray component, implying a cool localized component, possibly a relatively dense interstellar cloud interacting with the expanding shock front, superimposed on a more extended hotter region. The spectrum of N 49 showed a broad feature at 5303 A, identified with the forbidden Fe XIV line. Predictions of X-ray fluxes assuming a temperature of 2 x 10 to the 6th K and a density behind the shock front of 4/cu cm for hydrogen densities of zero and 10 to the 21st/sq cm lead to the suggestion that X-ray observations of N 49 may prove worthwhile.

Zarnecki, J. C.↗
NASA NTRS1991

Ionization fronts and shocked flows - The structure of the Orion Nebula at 0.1 arcsec

Initial results are presented from images of the Orion Nebula obtained with the HST Wide-Field Camera with a resolution of better than about 10 to the 15th cm. The morphology of the forbidden S II emission is markedly different from that seen in H-beta and forbidden O II. The forbidden S II is dominated by filamentary features with widths between 0.1 and 1 arcsesc which sharply highlight ionization fronts moving into dense neutral material. While the surfaces into which these fronts are moving are textured, subarcsec clumps with high density contrast are uncommon. The fields contains a number of HH objects whose structure is revealed by the HST, and which are described.

Hester, J. Jeff↗