SEARCH · Search NASA

Results for “Accelerators”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Current and future uses of accelerators in particle astrophysics

Beams of artificially accelerated heavy ions, protons, antiprotons, electrons, and positrons currently available at (and planned for) numerous facilities around the world are a valuable resource to the Cosmic Ray community. Such beams have been used to test detector concepts, calibrate balloon-borne and space flight experiments and to measure fundamental nuclear physics parameter necessary for the interpretation of Cosmic Ray data. As new experiments are flown the quality and extent of Cosmic Ray measurements will continue to improve. It will be necessary to increase activity at ground based accelerators in order to test/calibrate these new instruments and to maintain (or possibly improve) the ability to interpret these data. In this area, the newly formed Transport Collaboration, supported by NASA, will be providing new nuclear interaction cross section measurements for beams with Z less than or = 58 and supporting new instrument calibrations at the Lawrence Berkeley Laboratory Bevalac accelerator.

Guzik, T. G.↗

NASA NTRS1991

Investigation of hypersonic ramjet propulsion cycles using a ram accelerator test facility

Experimental research on hypersonic propulsion using a ram accelerator test facility is presented. The gasdynamics of the ram accelerator has been studied experimentally in a 38-mm bore facility over the Mach number range of 2.5 to 8.5, using methane- and ethylene-based propellant mixtures. Three different propulsive modes, centered on the Chapman-Jouguet (C-J) detonation speed of the combustible gas, have been experimentally observed. Projectiles have been accelerated smoothly from velocities below to above the C-J speed within a single propellant mixture.

Bruckner, A. P.↗

NASA NTRS1992

Bursts of transverse ion acceleration at rocket altitudes

High-time-resolution ion mass spectrometer distribution function measurements and wave data from a sounding rocket flight over an aurora have revealed the fine structure of the transverse ion acceleration mechanism in the upper ionosphere. The transversely accelerated ion (TAI) events can occur in a volume with a cross-field dimension as small as several tens of meters and thus appear as 50-100 ms ion bursts due to the rocket payload motion. Bulk heating to a characteristic energy of several eV and tail heating in the direction perpendicular to B of a few percent of ambient ions to a characteristic energy the order of 10 eV occur for both hydrogen and oxygen ions. The TAI at 90 deg pitch angle occur in localized regions of intense lower hybrid waves and in regions of density depletion. On close examination of the correlation between the wave bursts and the TAI it is believed that the waves produce the ion acceleration. The TAI occur during periods of field-aligned auroral electron bursts. Finally, near 1000 km altitude they occur about once every second. If the event presented here is considered average, the flux of TAI oxygen ions above 7 eV could account for the ion conic fluxes measured by the ISIS spacecraft.

Arnoldy, R. L.↗

NASA NTRS1992

Development of and flight results from the Space Acceleration Measurement System (SAMS)

This paper describes the development of and flight results from the Space Acceleration Measurement System (SAMS) flight units used in the Orbiter middeck, Spacelab module and the Orbiter cargo bay. The SAMS units are general purpose microgravity accelerometers designed to support a variety of science experiments with microgravity acceleration measurements. A total of six flight units have been fabricated; four for use in the Orbiter middeck and Spacelab module, and two for use in the Orbiter cargo bay. The design of the units is briefly described. The initial two flights of SAMS units on STS-40 (June 1991) and STS-43 (August 1991) resulted in 371 megabytes and 2.6 gigabytes of data, respectively. Analytical techniques developed to examine this quantity of acceleration data are described and sample plots of analyzed data are illustrated. Future missions for the SAMS units are listed.

Delombard, Richard↗

NASA NTRS1992

Proton acceleration in neutron star magnetospheres

To explain the emission of TeV and PeV gamma rays from accreting X-ray binary sources, protons must be accelerated to several times the gamma-ray energy. It is shown here that at certain times, the plasma in the accretion column of the neutron star may form a deep enough pool that the top portion becomes unstable to convective motions in spite of the strong magnetic field. The resulting turbulence produces fluctuations in the strength of the magnetic field that travel up the accretion column, taking energy out to the region of the energetic protons. The protons resonantly absorb this energy and are accelerated to high energies. Including the synchrotron radiation losses of the protons, it is shown that they can be accelerated to energies that are high enough to explain the gamma-ray observations.

Smith, I. A.↗

NASA NTRS1990

Acceleration, transport of and radiation by electrons in impulsive phase of flares

Recent work carried out in connection with various manifestations of the impulsive phase of solar flares is reviewed. Characteristics of accelerated electrons are determined, taking into account various possible interactions that electrons undergo as they traverse the flare plasma, and the expected radiation is evaluated via several mechanisms. Constraints are set on the characteristics of the accelerated electrons and on some properties of the flare plasma. Results obtained from comparisons with SMM and other observations of flares during the past solar cycle are described. It is shown that limits can be set on the range and distribution of the accelerated electron spectrum and pitch angle distribution, and on the column depth and field convergence rate of the flaring loop.

Petrosian, Vahe↗

NASA NTRS1992

Control of robot dynamics using acceleration control

Acceleration control of robotic devices can provide improvements to many space-based operations using flexible manipulators and to ground-based operations requiring better precision and efficiency than current industrial robots can provide. This paper reports on a preliminary study of acceleration measurement on robotic motion during parabolic flights on the NASA KC-135 and a parallel study of accelerations with and without gravity arising from computer simulated motions using TREETOPS software.

Workman, G. L.↗

NASA NTRS1991

Accelerated particles in solar flares

The variety of accelerated particle phenomena in solar flares is reviewed, including particle observation in interplanetary space and gamma-ray, neutron, hard X-ray, and radio emissions. It is emphasized that a significant or perhaps even large fraction of the total solar-flare energy is in accelerated particles. It is pointed out that the majority of the particles that produce impulsive flare phenomena remain trapped at the sun, probably due to confinement in the flaring magnetic loops. Gamma-ray observations are used to calculate the current rate of irradiation of the sun by MeV protons accelerated in solar flares. The current number of escaping protons is compared with irradiation rates of meteorites implied by observations of isotopic anomalies, and it is found that, except for the Ne-21 anomaly, enhanced proton irradiations from the ancient sun could not have been responsible for the observed isotopic anomalies.

Ramaty, R.↗

NASA NTRS1992

STS-40 orbital acceleration research experiment flight results during a typical sleep period

The Orbital Acceleration Research Experiment (OARE), an electrostatic accelerometer package with complete on-orbit calibration capabilities was flown aboard Shuttle on STS-40. The instrument is designed to measure and record the Shuttle aerodynamic acceleration environment from the free molecule flow regime through the rarefied flow transition into the hypersonic continuum regime. Because of its sensitivity, the OARE instrument detects aerodynamic behavior of the Shuttle while in low-earth orbit. A 2-h orbital time period on day seven of the mission, when the crew was asleep and other spacecraft activities were at a minimum, was examined. Examination of the model with the flight data shows the instrument to be sensitive to all major expected low-frequency acceleration phenomena; however, some erratic instrument bias behavior persists in two axes. In these axes, the OARE data can be made to match a comprehensive atmospheric-aerodynamic model by making bias adjustments and slight liner corrections for drift.

Blanchard, Robert C.↗

NASA NTRS1992

High spatial resolution measurements in a single stage ram accelerator

High spatial resolution experimental tube wall pressure measurements of ram accelerator gas dynamic phenomena are presented in this paper. The ram accelerator is a ramjet-in-tube device which operates in a manner similar to that of a conventional ramjet. The projectile resembles the centerbody of a ramjet and travels supersonically through a tube filled with a combustible gaseous mixture, with the tube acting as the outer cowling. Pressure data are recorded as the projectile passes by sensors mounted in the tube wall at various locations along the tube. Utilization of special highly instrumented sections of tube has allowed the recording of gas dynamic phenomena with high resolution. High spatial resolution tube wall pressure data from the three regimes of propulsion studied to date (subdetonative, transdetonative, and superdetonative) in a single stage gas mixture are presented and reveal the three-dimensional character of the flow field induced by projectile fins and the canting of the fins and the canting of the projectile body relative to the tube wall. Also presented for comparison to the experimental data are calculations made with an inviscid, three-dimensional CFD code. The knowledge gained from these experiments and simulations is useful in understanding the underlying nature of ram accelerator propulsive regimes, as well as assisting in the validation of three-dimensional CFD coded which model unsteady, chemically reactive flows.

Hinkey, J. B.↗

NASA NTRS1992

Issues on human acceleration tolerance after long-duration space flights

This report reviewed the literature on human tolerance to acceleration at 1 G and changes in tolerance after exposure to hypogravic fields. It was found that human tolerance decreased after exposure to hypokinetic and hypogravic fields, but the magnitude of such reduction ranged from 0 to 30 percent for plateau G forces and 30 to 70 percent for time tolerance on sustained G forces. A logistic regression model of the probability of individuals with 25 percent reduction in +Gz tolerance after 1 to 41 days of hypogravic exposures was constructed. The estimated values from the model showed a good correlation with the observed data. A brief review of the need for in-flight centrifuge during long-duration missions was also presented. Review of the available data showed that the use of countermeasures (such as anti-G suits, periodic acceleration, and exercise) reduced the decrement in acceleration tolerance after long-duration space flights. Areas of further research include quantification of the effect of countermeasures on tolerance, and methods to augment tolerance during and after exposures to hypogravic fields. Such data are essential for planning long-duration human missions.

Kumar, K. Vasantha↗

NASA NTRS1992

A redshift survey of IRAS galaxies. V - The acceleration on the Local Group

The acceleration on the Local Group is calculated based on a full-sky redshift survey of 5288 galaxies detected by IRAS. A formalism is developed to compute the distribution function of the IRAS acceleration for a given power spectrum of initial perturbations. The computed acceleration on the Local Group points 18-28 deg from the direction of the Local Group peculiar velocity vector. The data suggest that the CMB dipole is indeed due to the motion of the Local Group, that this motion is gravitationally induced, and that the distribution of IRAS galaxies on large scales is related to that of dark matter by a simple linear biasing model.

Strauss, Michael A.↗

NASA NTRS1992

Stochastic acceleration of electrons. I - Effects of collisions in solar flares

Stochastic acceleration of thermal electrons to nonrelativistic energies is studied under solar flare conditions. We show that, in turbulent regions, electron-whistler wave interactions can result in the acceleration of electrons in times comparable to or shorter than the Coulomb collision time. The kinetic equation describing the evolution of the electron energy distribution including stochastic acceleration by whistlers and energy loss via Coulomb interactions is solved for an initial thermal electron energy spectrum. In general, the shape of the resulting electron distributions are characterized by the energy E(c) where systematic energy gain by turbulence equals energy loss due to Coulomb collisions. For energies less than E(c), the spectra are steep (quasi-thermal) whereas above E(c), the spectra are power laws. We find that hard X-ray spectra computed using the electron distributions obtained from our numerical simulations are able to explain the complex spectral shapes and variations observed in impulsive hard X-ray bursts. In particular, we show that the gradual steepening observed by Lin et al. (1981) could be due to a systematic increase in the density of the plasma (due to evaporation) and the increasing importance of collisions instead of the appearance of a superhot thermal component.

Hamilton, Russell J.↗

NASA NTRS1992

The energy spectra of solar flare hydrogen, helium, oxygen, and iron - Evidence for stochastic acceleration

The time-integrated differential energy spectra of H, He, O, and Fe measured in 10 large flare events observed at 1 AU over the energy range of 0.3-80 MeV/nucleon showed consistent patterns in their spectral shapes: particles with larger mean mass-to-charge ratios were generally less abundant at higher energies. A steady state model of stochastic particle acceleration with rigidity-dependent diffusion coefficients fit the spectra best; spectra representative of diffusive shock acceleration also described the spectra of some events with the same number of free parameters, but often fell off faster in energy above 30 MeV per nucleon than the observations. The two model predictions differed most at energies near 0.1 MeV per nucleon, below the lowest energies observed in this study. The stochastic model quantitatively described the observed spectral ordering with less efficient acceleration of species with larger mean mass-to-charge ratios.

Mazur, J. E.↗

NASA NTRS1992

High-energy particle acceleration by explosive electromagnetic interaction in an accretion disk

By examining electromagnetic field evolution occurring in an accretion disk around a compact object, we arrive at an explosive mechanism of particle acceleration. Flux-freezing in the differentially rotating disk causes the seed and/or generated magnetic field to wrap up tightly, becoming highly sheared and locally predominantly azimuthal in orientation. We show how asymptotically nonlinear solutions for the electromagnetic fields may arise in isolated plasma blobs as a result of the driving of the fluid equations by the accretion flow. These fields are capable of rapidly accelerating charged particles from the disk. Acceleration through the present mechanism from AGN can give rise to energies beyond 10 exp 20 eV. Such a mechanism may present an explanation for the extragalactic origin of the most energetic observed cosmic rays.

Haswell, C. A.↗

NASA NTRS1993

Cosmic-ray acceleration during the impact of shocks on dense clouds

In order to elucidate the properties of diffusive shock acceleration in nonuniform environments, an extensive set of simulations of the dynamical interactions between plane nonradiative shocks and dense gas clouds was carried out initially in static equilibrium with their environments. These time-dependent calculations are based on the two-fluid model for diffusive cosmic ray transport, and include the dynamically active energetic proton component of the cosmic rays as well as passive electron and magnetic field components. Except when the incident shock is itself already dominated by cosmic ray pressure, it is found that the presence of the cloud adds little to the net acceleration efficiency of the original shock and can, in fact, reduce slightly the net amount of energy transferred to cosmic rays after a given time. It is found that, in 2D cloud simulations, the always-weak bow shock and the shock inside the cloud are less important to acceleration during the interaction than the tail shock.

Jones, T. W.↗

NASA NTRS1993

The role of magnetic loops in particle acceleration at nearly perpendicular shocks

The acceleration of superthermal ions is investigated when a planar shock that is on average nearly perpendicular propagates through a plasma in which the magnetic field is the superposition of a constant uniform component plus a random field of transverse hydromagnetic fluctuations. The importance of the broadband nature of the transverse magnetic fluctuations in mediating ion acceleration at nearly perpendicular shocks is pointed out. Specifically, the fluctuations are composed of short-wavelength components which scatter ions in pitch angle and long-wavelength components which are responsible for a spatial meandering of field lines about the mean field. At nearly perpendicular shocks the field line meandering produces a distribution of transient loops along the shock. As an application of this model, the acceleration of a superthermal monoenergetic population of seed protons at a perpendicular shock is investigated by integrating along the exact phase-space orbits.

Decker, R. B.↗

NASA NTRS1993

Ponderomotive effects on ion acceleration in the auroral zone

Low frequency, large amplitude Alfven waves occur in the auroral zone. Such waves have a ponderomotive effect on both ions and electrons. In the region between the large wave field and the ionosphere, the ponderomotive force accelerates electrons downward and ions upward, which produces an ambipolar electric field. The combined effect is to produce a differential acceleration between O(+) and H(+) with the O(+) accelerated more out of the ionosphere. The typical resulting energization for O(+) is tens of eV, which is sufficient for the ions to escape the ionosphere. We demonstrate this by means of analysis and test-particle calculation.

Li, Xinlin↗