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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Impact experiments. I - Ejecta velocity distributions and related results from regolith targets

Results are reported of laboratory measurements of the velocity distributions of powdery ejecta of 14 impacts into powders simulating regolith in near vacuum. The impact velocities ranged from 5-2321 m/sec, a velocity range believed prevalent in the early solar system. The powder was mechanically similar to lunar regolith. The projectiles comprised harder materials than the regolith, i.e., pyrex spheres, basalt spheres and cylinders, and igneous rocks. High-speed photography was employed to record the events. The differences between the present results and those from hypervelocity impacts are discussed in detail. Notably, an impact velocity threshold was detected between 10-30 m/sec, below which the amount of ejecta is less than the projectile mass.

Hartmann, W. K.↗
DOE OSTI2013

Development of a compact thermal lithium atom beam source for measurements of electron velocity distribution function anisotropy in electron cyclotron resonance plasmas

The anisotropy of the electron velocity distribution function (EVDF) in plasmas can be deduced from the polarization of emissions induced by anisotropic electron-impact excitation. In this paper, we develop a compact thermal lithium atom beam source for spatially resolved measurements of the EVDF anisotropy in electron cyclotron resonance (ECR) plasmas. The beam system is designed such that the ejected beam has a slab shape, and the beam direction is variable. The divergence and flux of the beam are evaluated by experiments and calculations. The developed beam system is installed in an ECR plasma device with a cusp magnetic field, and the LiI 2s–2p emission (670.8 nm) is observed in low-pressure helium plasma. The two-dimensional distributions of the degree and direction of the polarization in the LiI emission are measured by a polarization imaging system. The evaluated polarization distribution suggests the spatial variation of the EVDF anisotropy.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1959

An Equation for the Mean Velocity Distribution of Boundary Layers

A general relation, empirical in origin, for the mean velocity distribution of both laminar and turbulent boundary layers is proposed. The equation, in general, accurately describes the profiles in both laminar and turbulent flows. The calculation of profiles is based on a prior knowledge of momentum, displacement, and boundary-layer thickness together with free-stream conditions. The form for turbulent layers agrees with the present concepts of similarity of the outer layer. For the inner region or turbulent boundary layers the present relation agrees very closely with experimental measurements even in cases where the logarithmic law of the wall is inadequate. A unique relation between profile form factors and the ratio of displacement thickness to boundary-layer thickness is obtained for turbulent separation. A similar criterion is also obtained for laminar separation. These relations are demonstrated to serve as an accurate criterion for identifying separation in known profiles.

Sandborn, V. A.↗
NASA NTRS1988

On the long-tail solar wind electron velocity distribution

The role of the log-normal distribution in the description of the high-energy tail of the electron velocity distribution in the solar wind plasma is examined. Specifically, it is shown that the core-halo solar wind distribution function can be understood in terms of a simple phenomenological model of general applicability in which the core has a Maxwellian or normal distribution and the halo a log-normal distribution. In the presence of structures in the interplanetary medium capable of interacting with the electrons, the model predicts a transition at the highest velocities to a secondary halo distribution.

Shlesinger, Michael F.↗
NASA NTRS1994

A Monte Carlo simulation of the effect of ion self-collisions on the ion velocity distribution function in the high-latitude F-region

Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E x B drift and ion-neutral collisions. At high altitude and/or for solar maximum conditions, the ion-to-neutral density ratio increases and, hence, the role of ion self-collisions becomes appreciable. A Monte Carlo simulation was used to investigate the behavior of O(+) ions that are E x B-drifting through a background of neutral O, with the effect of O(+) (Coulomb) self-collisions included. Wide ranges of the ion-to-neutral density ratio n(sub i)/n(sub n) and the electrostatic field E were considered in order to investigate the change of ion behavior with solar cycle and with altitude. For low altitudes and/or solar minimum (n(sub i)/n(sub n) less than or equal to 10(exp -5)), the effect of self-collisions is negligible. For higher values of n(sub i)/n(sub n), the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O(+) distribution are reduced. The Monte Carlo results were compared to those that used simplified collision models in order to assess their validity. In general, the simple collision models tend to be more accurate for low E and for high n(sub i)/n(sub n).

Barghouthi, I. A.↗
DOE OSTI2016

Observations of the He{sup +} pickup ion torus velocity distribution function with SOHO/CELIAS/CTOF

Interstellar PickUp Ions (PUIs) are created from neutrals coming from the interstellar medium that get ionized inside the heliosphere. Once ionized, the freshly created ions are injected into the magnetized solar wind plasma with a highly anisotropic torus-shaped Velocity Distribution Function (VDF). It has been commonly assumed that wave-particle interactions rapidly destroy this torus by isotropizing the distribution in one hemisphere of velocity space. However, recent observations of a He{sup +} torus distribution using PLASTIC on STEREO showed that the assumption of a rapid isotropization is oversimplified. The aim of this work is to complement these studies. Using He{sup +} data from the Charge Time-Of-Flight (CTOF) sensor of the Charge, ELement, and Isotope Analysis System (CELIAS) on-board the SOlar and Heliospheric Observatory (SOHO) and magnetic field data from the Magnetic Field Investigation (MFI) magnetometer of the WIND spacecraft, we derive the projected 1-D VDF of He{sup +} for different magnetic field configurations. Depending on the magnetic field direction, the initial torus VDF lies inside CTOF’s aperture or not. By comparing the VDFs derived under different magnetic field directions with each other we reveal an anisotropic signature of the He{sup +} VDF.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Effects of coherent offset of velocity distribution in electron coolers on ion dynamics

We revisit the effect of coherent offset in velocity distribution of the electron beam in electron coolers and consider its implications for the dynamics of the cooled ion bunch. This effect becomes of special importance for high-energy electron coolers due to reduction of transverse angular spread with energy, thus requiring strict control. As an example, estimates of the severity of and the possibility to observe the considered effects for LEReC case are discussed.

43 PARTICLE ACCELERATORS↗
NASA NTRS1979

Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. Paper 2: The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen

Non-Maxwellian electron velocity distribution functions, previously computed for Dupree's model of the solar transition region are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation.

Roussel-Dupre, R.↗
NASA NTRS1990

Solar wind proton velocity distributions - Comparison of the bi-Maxwellian based 16-moment expansion with observations

The purpose of this paper is to study the possible types of velocity distributions that can be obtained from the bi-Maxwellian based 16-moment expansion of the distribution function, assuming macroscopic parameter values characteristic of the range of solar wind conditions. While previous studies also took heat flow into account, the theoretical expansions for f and the definitions of the physical moments adopted in these studies were different from those used in this paper. The choice of the 16-moment expansion and corresponding moment definitions was motivated by the fact that this is the correct generalization of the widely-used Maxwellian-based 13-moment expansion to the case where the zeroth-order distribution is a bi-Maxwellian. It is found that most of the features characteristic of solar wind proton distributions can be reproduced with the 16-moment distribution, including the appearance of secondary peaks. It is also shown how each of the physically significant velocity moments affects the shape of the distribution function.

Demars, H. G.↗
NASA NTRS1986

Velocity distributions of ion beams in the plasma sheet boundary layer

The value of measured ion-beam velocity distributions as diagnostic tools to characterize the propagation and acceleration of particle beams in the plasma-sheet boundary layer is assessed. Models based on adiabatic deformation of a flowing Maxwellian, acceleration by field-aligned potentials, and current-sheet acceleration are fitted to observational data, and the results are presented in extensive diagrams and graphs. The data are found to be consistent with models involving field-aligned or cross-tail potential drops, but not with models based solely on the adiabatic deformation of initially isotropic distributions.

Eastman, T. E.↗
NASA NTRS1980

A Scanning laser-velocimeter technique for measuring two-dimensional wake-vortex velocity distributions

A rapid scanning two dimensional laser velocimeter (LV) has been used to measure simultaneously the vortex vertical and axial velocity distributions in the Langley Vortex Research Facility. This system utilized a two dimensional Bragg cell for removing flow direction ambiguity by translating the optical frequency for each velocity component, which was separated by band-pass filters. A rotational scan mechanism provided an incremental rapid scan to compensate for the large displacement of the vortex with time. The data were processed with a digital counter and an on-line minicomputer. Vaporized kerosene (0.5 micron to 5 micron particle sizes) was used for flow visualization and LV scattering centers. The overall measured mean-velocity uncertainity is less than 2 percent. These measurements were obtained from ensemble averaging of individual realizations.

Gartrell, L. R.↗
NASA NTRS1992

Development of the mean velocity distribution in rectangular jets

The mean flowfield of 1 x 2 and 1 x 4 aspect ratio rectangular jets has been measured using a laser Doppler anemometer system. The development of the downstream velocity distribution is analyzed with respect to centerline velocity decay, shear layer growth, axis switching, and velocity profile development. Comparisons are made with axisymmetric, planar, and other rectangular jets.

Morrison, G. L.↗