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Crawford, F. W.

Publications and source records attributed to Crawford, F. W..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Variational calculations for resonance oscillations of inhomogeneous plasmas

The electrostatic resonance properties of an inhomogeneous plasma column are reported by application of the Rayleigh-Ritz method. A description of the rf equation of motion and pressure term that expresses the system of equations in Euler-Lagrange form is presented. The Rayleigh-Ritz procedure is applied to the corresponding Lagrangian to obtain approximate resonance frequencies and eigenfunctions. An appropriate set of trial coordinate functions is defined, which leads to frequency and eigenfunction estimates.

Peng, Y. K. M.↗
NASA NTRS1973

Low-frequency flute instabilities of a hollow cathode arc discharge - Theory and experiment.

The characteristics of two low-frequency electrostatic flute instabilities of a low-pressure hollow cathode arc discharge are reported. Mode I has azimuthal mode number m = 1, and occurs when the radial electric field is negative (directed inward), while mode II has m = - 1 and occurs when the field is positive. The radial electric field is controlled by varying the potential of a secondary anode cylinder located close to the outer discharge radius. A linear perturbation analysis, based on the two-fluid equations, is given for a low-beta, collisionless, cylindrical plasma column, immersed in a uniform axial magnetic field, having a Gaussian density profile and an arbitrary radial electric field profile. Reasonable correlation between theory and experiment is demonstrated for both modes.

Ilic, D. B.↗
NASA NTRS1973

A theory for scattering by density fluctuations based on three-wave interaction

The theory of scattering by charged particle fluctuations of a plasma is developed for the case of zero magnetic field. The source current is derived on the basis of: (1) a three wave interaction between the incident and scattered electromagnetic waves and one electrostatic plasma wave (either Langmuir or ion acoustic), and (2) a synchronous interaction between the same two electromagnetic waves and the discrete components of the charged particle fluctuations. Previous work is generalized by no longer making the assumption that the frequency of the electromagnetic waves in large compared to the plasma frequency. The general result is then applied to incoherent scatter, and to scatter by strongly driven plasma waves. An expansion is carried out for each of those cases to determine the lower order corrections to the usual high frequency scattering formulas.

Harker, K. J.↗
NASA NTRS1972

Energy absorption in cold inhomogeneous plasmas - The Herlofson paradox.

Confirmation of Barston's (1964) conclusions regarding the underlying mechanism of the Herlofson paradox by examining in detail several analytically tractable cases of delta-function and sinusoidal excitation. The effects of collisions and nonzero electron temperature in determining the steady state fields and dissipation are considered. Energy absorption without dissipation in plasmas is shown to be analogous to that occurring after application of a signal to a network of lossless resonant circuits. This analogy is pursued and is extended to cover Landau damping in a warm homogeneous plasma in which the resonating elements are the electron streams making up the velocity distribution. Some of the practical consequences of resonant absorption are discussed, together with a number of paradoxical plasma phenomena which can also be elucidated by considering a superposition of normal modes rather than a single Fourier component.

Crawford, F. W.↗
NASA NTRS1971

Observations of nonlinear scattering from a plasma column.

Nonlinear interaction effects are considered for signals incident on an unmagnetized cold plasma column, without making the quasi-static approximation. It is found that the nonlinearly generated quadrupole component is only modified slightly and that no multipolar component can give a forward- or back-scattered signal. However, strong nonlinear forward scattering was observed in previous experiments. This spurious result has been traced to the effect of the earth's magnetic field. When this is cancelled, predominantly quadrupolar radiation is observed, in agreement with theory.

Bruce, R. L.↗
NASA NTRS1970

Stability analysis of whistler amplification

Whistler amplification in magnetosphere for electron interaction with background plasma to produce wave growth, discussing stability of various anisotropic velocity distributions

Crawford, F. W.↗
NASA NTRS1970

Some studies of whistler instability

Whistler instability examined on gyrating electron beam interaction with cold background plasma propagating parallel to magnetic field

Crawford, F. W.↗
NASA NTRS1970

Laboratory plasma resonances

Stable plasma resonance behavior, calculating small signal and nonlinear responses for theory verification and diagnostic techniques

Crawford, F. W.↗