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At least 1,027 records · Page 57
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NASA NTRS1989

Correlation between X-ray flux and rotational acceleration in Vela X-1

The results of a search for correlations between X-ray flux and angular acceleration for the accreting binary pulsar Vela X-1 are presented. Results are based on data obtained with the Hakucho satellite during the interval 1982 to 1984. In undertaking this correlation analysis, it was necessary to modify the usual statistical method to deal with conditions imposed by generally unavoidable satellite observing constraints, most notably a mismatch in sampling between the two variables. The results are suggestive of a correlation between flux and the absolute value of the angular acceleration, at a significance level of 96 percent. The implications of the methods and results for future observations and analysis are discussed.

Deeter, J. E.↗
NASA NTRS1988

Space Experiments with Particle Accelerators (SEPAC)

The purpose of Space Experiments with Particle Accelerators (SEPAC) on the Atmospheric Laboratory for Applications and Science (ATLAS 1) mission, is to carry out active and interactive experiments on and in the earth's ionosphere, atmosphere, and magnetosphere. The instruments to be used are an electron beam accelerator (EBA), plasma contactor, and associated instruments the purpose of which is to perform diagnostic, monitoring, and general data taking functions. Four major classes of investigations are to be performed by SEPAC. They are: beam plasma physics, beam-atmosphere interactions, the use of modulated electron beams as transmitting antennas, and the use of electron beams for remote sensing of electric and magnetic fields. The first class consists mainly of onboard plasma physics experiments to measure the effects of phenomena in the vicinity of the shuttle. The last three are concerned with remote effects and are supported by other ATLAS 1 investigations as well as by ground-based observations.

Obayashi, Tatsuzo↗
NASA NTRS1988

Particle acceleration in impulsive solar flares

A model for second-step electron acceleration in impulsive solar flares is presented. The theory of stochastic particle acceleration is extended to include Coulomb energy losses which become important at low coronal heights. This inclusion successfully explains the observed steepening of interplanetary electron spectra below about 3 MeV following impulsive solar flares taking place at low coronal heights. It also explains the observed spectral differences of relativistic electrons in long-duration and impulsive flares.

Steinacker, J.↗
NASA NTRS1988

Charging and the cross-field discharge during electron accelerator operation on a rocket

Preliminary results are presented from experiments to study the neutralization processes around an electron beam emitting rocket. The rocket, SCEX II, was flown on January 31, 1987 from Alaska, with a payload consisting of two independent electron accelerators and two arms with conducting elements to act as Langmuir probes and to measure floating potentials. It was expected that electrons in the strong electric fields around the charged rocket would gain sufficient energy to ionize neutrals, producing ions which would be hurled outward at energies up to the rocket potential. Three hemispherical retarding potential analyzers were ejected from the main payload to measure these ions. The measurements show that fields sufficient to accelerate electrons to ionizing energies were present around the rocket.

Kellogg, Paul J.↗
NASA NTRS1988

Particle acceleration and wave emissions associated with the formation of auroral cavities and enhancements

A unified model is presented which interrelates the various processes involved in auroral particle acceleration and the associated wave emissions, and it is shown how energy is coupled from the magnetosphere into the ionosphere. The phenomena in the magnetotail which can provide the source of free energy for the perpendicular electrostatic shocks are identified along with the associated potential structures in the nightside auroral region. The characteristics of the particle acceleration produced by the shock are described, including efficiency and energy transport between magnetospheric and ionospheric plasmas, the properties of the particle distributions throughout the shock region and return current regions, and the associated wave emissions. The source of free energy for the generation of ion conics is identified, as are the signatures for the formation of plasma cavities and/or enhancements.

Winglee, R. M.↗
NASA NTRS1989

Magnetohydrodynamic waves and particle acceleration in a coronal loop

A model is presented for the acceleration of electrons in a flaring solar coronal loop. It is suggested that the primary energy release event in the flare establishes a spectrum of MHD waves within the loop which accelerate electrons by wave-particle resonant interactions. The nature of the MHD oscillations are described and numerical and analytic solution of the dispersion relation are examined. It is found that the behavior of a particle depends on whether or not it is in resonance with the wave spectrum. Resonant particles follow chaotic trajectories and can diffuse in velocity space between wave effective potentials, thereby gaining energy.

De La Beaujardiere, Jean-Francois↗
NASA NTRS1989

Electron acceleration by an obliquely propagating electromagnetic wave in the regime of validity of the Fokker-Planck-Kolmogorov approach

The relativistic motion of an ensemble of electrons in an intense monochromatic electromagnetic wave propagating obliquely in a uniform external magnetic field is studied. The problem is formulated from the viewpoint of Hamiltonian theory and the Fokker-Planck-Kolmogorov approach analyzed by Hizanidis (1989), leading to a one-dimensional diffusive acceleration along paths of constant zeroth-order generalized Hamiltonian. For values of the wave amplitude and the propagating angle inside the analytically predicted stochastic region, the numerical results suggest that the diffusion probes proceeds in stages. In the first stage, the electrons are accelerated to relatively high energies by sampling the first few overlapping resonances one by one. During that stage, the ensemble-average square deviation of the variable involved scales quadratically with time. During the second stage, they scale linearly with time. For much longer times, deviation from linear scaling slowly sets in.

Hizanidis, Kyriakos↗
NASA NTRS1988

Simulation of launch and re-entry acceleration profiles for testing of Shuttle and unmanned microgravity research payloads

A procedure was developed for the simulation of the launch and reentry acceleration profiles of the Space Shuttle (3.3 and 1.7 g maximum, respectively) and of two versions of NASA's proposed materials research Reusable Reentry Satellite (RRS) (8 and 4 g maximum, respectively). With a 7-m centrifuge, the time dependence of five different acceleration episodes was simulated for payload masses up to 59 kg. Test results obtained for the Materials Dispersion Apparatus, a commercial low-cost payload device, are presented.

Cassanto, J. M.↗
NASA NTRS1989

Anisotropy of shock-accelerated ion distributions in interplanetary space

The discrepancy between theory and observation is discussed with regard to the ability of interplanetary shock waves to accelerate a small percentage of the thermal ion population. The major point of departure rests with the spatial dependence of the energetic particle intensity and anisotropy in the region upstream of interplanetary shocks. It is argued that the discrepancy is due to the presence of solar flare particles forming an additional seed population which alters the upstream boundary condition of the energetic population. The resulting anisotropy of the energetic particle distribution several scale lengths upstream of the shock is proportional to the ratio of the streaming of the shock-accelerated population to the density of the solar flare population. This theory is then compared with the results of observed upstream anisotropy and measured particle intensities and anisotropies.

Smith, Charles W.↗
NASA NTRS1989

Numerical studies of multiple-encounter shock drift acceleration

Test particle simulation is performed to examine the mechanism previously proposed by Chiueh for particle acceleration by a nearly perpendicular shock where only downstream MHD turbulence is present. A nonnegligible fraction of low-energy particles is observed gaining energy by more than three orders of magnitude in a few hundred cyclotron periods. Criteria for effective acceleration given previously are examined and confirmed. The numerical results suggest that in the nonrelativistic energy range, a power-law particle energy spectrum, with the power index determined by the degree to which the criteria are satisfied, may form.

Chiueh, Tzihong↗
NASA NTRS1989

Convergence acceleration of viscous and inviscid hypersonic flow calculations

The convergence of inviscid and viscous hypersonic flow calculations using a two-dimensional flux-splitting code is accelerated by applying a Richardson-type overrelaxation method. Successful results are presented for various cases; and a 50 percent savings in computer time is usually achieved. An analytical formula for the overrelaxation factor is derived, and the performance of this scheme is confirmed numerically. Moreover, application of this overrelaxation scheme produces a favorable preconditioning for Wynn's epsilon-algorithm. Both techniques have been extended to viscous three-dimensional flows and applied to accelerate the convergence of the compressible Navier-Stokes code. A savings of 40 percent in computer time is achieved in this case.

Cheer, A.↗
NASA NTRS1988

Acceleration levels on board the Space Station and a tethered elevator for micro and variable-gravity applications

This paper investigates the dynamics and acceleration levels of a new tethered system for micro and variable-gravity applications. The system consists of two platforms tethered on opposite sides to the Space Station. A fourth platform, the elevator, is placed in between the Space Station and the upper platform. Variable-g levels on board the elevator are obtained by moving this facility along the upper tether, while micro-g experiments are carried out on board the Space Station. By controlling the length of the lower tether the position of the system CM can be maintained on board the Space Station despite variations of the station's distribution of mass. The paper illustrates the mathematical model, the environmental perturbations and the control techniques which have been adopted for the simulation and control of the system dynamics. Two sets of results from two different simulation runs are shown. The first set shows the system dynamics and the acceleration spectra on board the Space Station and the elevator during station-keeping. The second set of results demonstrates the capability of the elevator to attain a preselected g-level.

Lorenzini, E. C.↗
NASA NTRS1989

Interplanetary observational constraints on Alfven wave acceleration of the solar wind

Spacecraft and interplanetary remote sensing observations of wave spectra are used to constrain the possible role of Alfven waves in the acceleration of high-speed streams in the solar wind. The observations suggest a method for extrapolating the wave energy flux near 1 AU back to the sun in a way that accounts for dissipation. Applying this method both for typical parameters and in the case of a well-studied high-speed stream leads to the conclusion that the Alfven waves observed in the solar wind were not sufficiently energetic near the sun to accelerate the streams.

Roberts, D. A.↗
NASA NTRS1989

Heating and acceleration of heavy ions during solar flares

The heating of the various ion species during solar flares is examined in an attempt to develop a unified model incorporating the enrichments in abundances seen by ISEE 3 and some of the characteristics of the soft X-ray line emissions. Problems associated with identifying the initial conditions and the driving mechanisms for the particle acceleration are addressed. The acceleration of heated plasma ions as they propagate upward into the corona is studied via particle simulations.

Winglee, R. M.↗
NASA NTRS1989

Calculation of structural dynamic forces and stresses using mode acceleration

While the standard mode acceleration formulation in structural dynamics has often been interpreted to suggest that the reason for improved convergence obtainable is that the dynamic correction factor is divided by the modal frequencies-squared, an alternative formulation is presented which clearly indicates that the only difference between mode acceleration and mode displacement data recovery is the addition of a static correction term. Attention is given to the advantages in numerical implementation associated with this alternative, as well as to an illustrative example.

Blelloch, Paul↗
NASA NTRS1989

Vortex paradigm for shock-accelerated density-stratified interfaces

Numerical simulations are reported that capture the observations of Haas and Sturtevant (1985) when a planar shock accelerates an inclined planar interface between two media. A vortex paradigm is presented for interpreting the evolution of shock-accelerated density-stratified interfaces beyond early times. The simulations illustrate the paradigm and are in good agreement with the results of Haas and Sturtevant. Color images of space-time diagrams of the one-space integrated vorticity function are given to show the primary and secondary features of the emerging vortex structures.

Hawley, John F.↗
NASA NTRS1989

Joule heating and runaway electron acceleration in a solar flare

The hard and soft x ray and microwave emissions from a solar flare (May 14, 1980) were analyzed and interpreted in terms of Joule heating and runaway electron acceleration in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft x ray emitting plasma can only be heated by a single current sheet if the resistivity in the sheet is well above the classical, collisional resistivity of 10(exp 7) K, 10(exp 11)/cu cm plasma. If the hard x ray emission is from thermal electrons, anomalous resistivity or densities exceeding 3 x 10(exp 12)/cu cm are required. If the hard x ray emission is from nonthermal electrons, the emissions can be produced with classical resistivity in the current sheets if the heating rate is approximately 4 times greater than that deduced from the soft x ray data (with a density of 10(exp 10)/cu cm in the soft x ray emitting region), if there are at least 10(exp 4) current sheets, and if the plasma properties in the sheets are characteristic of the superhot plasma observed in some flares by Lin et al., and with Hinotori. Most of the released energy goes directly into bulk heating, rather than accelerated particles.

Holman, Gordon D.↗
NASA NTRS1989

Free electron lasers driven by linear induction accelerators: High power radiation sources

The technology of Free Electron Lasers (FELs) and linear induction accelerators (LIAs) is addressed by outlining the following topics: fundamentals of FELs; basic concepts of linear induction accelerators; the Electron Laser Facility (a microwave FEL); PALADIN (an infrared FEL); magnetic switching; IMP; and future directions (relativistic klystrons). This presentation is represented by viewgraphs only.

Orzechowski, T. J.↗