Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Collision frequency”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Code Development Supporting a Non-Thermal Source of High Fluence Warm X-Ray

A six-month research effort has advanced the hybrid kinetic-fluid modeling capability required for developing non-thermal warm x-ray sources on Z. The three particle treatments of quasi-neutral, multi-fluid, and kinetic are demonstrated in 1D simulations of an Ar gas puff. The simulations determine required resolutions for the advanced implicit solution techniques and debug hybrid particle treatments with equation-of-state and radiation transport. The kinetic treatment is used in preliminary analysis of the non-Maxwellian nature of a gas target. It is also demonstrates the sensitivity of the cyclotron and collision frequencies in determining the transition from thermal to non-thermal particle populations. Finally, a 2D Ar gas puff simulation of a Z shot demonstrates the readiness to proceed with realistic target configurations. The results put us on a very firm footing to proceed to a full LDRD which includes continued development transition criteria and x-ray yield calculation.

36 MATERIALS SCIENCE↗
NASA NTRS1965

A microwave probe for plasma plumes.

Swinging-arm microwave probe to measure electron density and collision frequency profiles transverse to plasma jet plumes

MICROWAVE PLASMA PROBE↗
NASA NTRS1972

Partial reflections of radio waves from the lower ionosphere

The addition of phase difference measurements to partial reflection experiments is discussed, and some advantages of measuring electron density this way are pointed out. The additional information obtained reduces the requirement for an accurate predetermination of collision frequency. Calculations are also made to estimate the errors expected in partial-reflection experiments due to the assumption of Fresnel reflection and to the neglect of coupling between modes. In both cases, the errors are found to be of the same order as known errors in the measurements due to current instrumental limitations.

Connolly, D. J.↗
NASA NTRS1972

Differential phase measurements of D-region partial reflections

Differential phase partial reflection measurements were used to deduce D region electron density profiles. The phase difference was measured by taking sums and differences of amplitudes received on an array of crossed dipoles. The reflection model used was derived from Fresnel reflection theory. Seven profiles obtained over the period from 13 October 1971 to 5 November 1971 are presented, along with the results from simultaneous measurements of differential absorption. Some possible sources of error and error propagation are discussed. A collision frequency profile was deduced from the electron concentration calculated from differential phase and differential absorption.

Wiersma, D. J.↗
NASA NTRS1970

Dispersion discontinuities of strong collisionless shocks

Linear fluid equations are used to estimate wave train properties of strong collisionless shocks. Fast shocks exhibit several dispersion changes with increasing Mach number. For perpendicular propagation into a finite-beta plasma, an ion cyclotron radius trailing wave train exists only for (M sub F)2 is smaller than 2. Oblique fast shocks have a leading ion inertia wave train if M sub A is smaller than root of M(+)/M(-) cos theta/2 and a trailing electron inertia train if M sub A is greater than root of M(+)/M(-) cos theta/2. If the downstream sound speed exceeds the flow speed, linear wave theory predicts a trailing ion acoustic structure which probably resides within the magnetic shock. For a turbulent shock model in which an effective electron-ion collision frequency exceeds the lower hybrid frequency, ions decouple from the magnetic field; the shock wave train now trails with electron inertia and electron gyroradius lengths. Comparisons of this turbulent model and observations on the earth's bow shock are made.

Coroniti, F. V.↗
NASA NTRS1973

Propagation studies using a theoretical ionosphere model

The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.

Lee, M.↗
NASA NTRS1973

Theoretical and experimental studies of reentry plasmas

A viscous shock-layer analysis was developed and used to calculate nonequilibrium-flow species distributions in the plasma layer of the RAM vehicle. The theoretical electron-density results obtained are in good agreement with those measured in flight. A circular-aperture flush-mounted antenna was used to obtain a comparison between theoretical and experimental antenna admittance in the presence of ionized boundary layers of low collision frequency. The electron-temperature and electron-density distributions in the boundary layer were independently measured. The antenna admittance was measured using a four-probe microwave reflectometer and these measured values were found to be in good agreement with those predicted. Measurements were also performed with another type of circular-aperture antenna and good agreement was obtained between the calculations and the experimental results. A theoretical analysis has been completed which permits calculation of the nonequilibrium, viscous shock-layer flow field for a sphere-cone body. Results are presented for two different bodies at several different altitudes illustrating the influences of bluntness and chemical nonequilibrium on several gas dynamic parameters of interest. Plane-wave transmission coefficients were calculated for an approximate space-shuttle body using a typical trajectory.

Dunn, M. G.↗
NASA NTRS1973

Current distribution on an infinite tubular antenna immersed in a cold collisional magnetoplasma.

Based upon a boundary-value formulation, a new approximate expression is derived for the total axial current on an infinite antenna immersed in an unbounded, cold, collisional magnetoplasma with a dc magnetic field oriented parallel to the antenna. Numerical results are presented for the current distributions over plasma parameters corresponding to each of the eight regions of the Clemmow-Mullaly-Allis diagram and for different values of the collision frequency.

Bhat, B.↗
NASA NTRS1973

Antenna admittance determination of electron density.

A circular-aperture flush-mounted antenna for which a theoretical description of the antenna-plasma interaction has been developed was used to obtain a comparison between theoretical and experimental antenna admittance in the presence of ionized boundary layers of low-collision frequency. The antenna was located in a flat-plate model which was in turn located in the expanding-flow environment of a reflected-shock tunnel. The electron-temperature and electron-density distributions in the plate boundary layer at the antenna location were independently measured using voltage-swept thin-wire Langmuir probes for one of the test conditions. The antenna admittance was measured using a four-probe microwave reflectometer and these measured values were found to be in good agreement with those predicted from the theory. Measurements were also performed with another type of circular-aperture antenna which did not satisfy all of the constraints of the theoretical model, although good agreement was obtained between the calculations and the experimental results.

Dunn, M. G.↗
NASA NTRS1973

First measurements of electron temperature in the D region with a symmetric double probe

Measurement of the altitude profile of electron temperature in the ionospheric D region with the aid of a symmetric double probe flown on a Nike-Cajun payload launched on Oct. 13, 1971. The procedure for determining the electron temperature from the parameters of the double probe's current-voltage characteristic under conditions of nonnegligible ion-atom collision frequencies is described. It is shown that in its first lower ionospheric application the technique of the symmetric double probe has yielded the lowest values of electron temperature yet measured and has provided the very first direct measurement of electron temperature in the D region.

Szuszczewicz, E. P.↗
NASA NTRS1974

Correlation effects in the theory of combined Doppler and pressure broadening. I - Classical theory

An investigation is conducted of the combined effects of radiator-perturber collisions and radiator translational motion in the context of foreign gas broadening of optical transitions in neutral radiators. Questions concerning the speed-dependent collision frequency are considered and aspects of general theory are explored, taking into account the correlation function, the ensemble average, and the kinetic equation formalism. An elementary solution is discussed along with a one-perturber approximation, inverse power law model calculations, and a comparison with the Voigt profile.

Ward, J.↗
NASA NTRS1974

The collisional drift mode in a partially ionized plasma

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.↗
NASA NTRS1975

Propagation predictions and studies using a ray tracing program combined with a theoretical ionospheric model

Radio wave propagation predictions are described in which modern comprehensive theoretical ionospheric models are coupled with ray-tracing programs. In the computer code described, a network of electron density and collision frequency parameters along a band about the great circle path is calculated by specifying the transmitter and receiver geographic coordinates, time, the day number, and the 2800-MHz solar flux. The ray paths are calculated on specifying the frequency, mode, range of elevation angles, and range of azimuth angles from the great circle direction. The current program uses a combination of the Penn State MKI E and F region models and the Mitra-Rowe D and E region model. Application of the technique to the prediction of satellite to ground propagation and calculation of oblique incidence propagation paths and absorption are described. The implications of the study to the development of the next generation of ionospheric models are discussed.

Lee, M. K.↗
NASA NTRS1975

A comparison of the temperature and density structure in high and low speed thermal proton flows

Steady-state altitude profiles of H(+) density, drift velocity, and temperature and O(+) density and temperature were deduced for a wide range of H(+) outflow velocities from subsonic to supersonic flow for plasma densities typical of both undisturbed and trough regions of the ionsophere. Allowance was made for the effects of inertia, parallel stress, and the velocity dependence of the H(+) collision frequencies. It was found that at supersonic outflow velocities there is a decrease in H(+) temperature with increasing outflow velocity. The H(+) temperatures are substantially increased above the O(+) temperatures when H(+) is flowing, with T(H+)/T(O+) reaching a maximum ratio of about 3:1.

Raitt, W. J.↗