Engineering topics

Ilic, D. B.

Publications and source records attributed to Ilic, D. B..

6 records

NASA NTRS1979

Ionospheric wave spectrum measurements

The local spectrum S(k, omega) of either potential or electron-density fluctuations can be used to determine macroscopic-plasma characteristics such as the local density and temperature, transport coefficients, and drift current. This local spectrum can be determined by measuring the cross-power spectrum. The paper examines the practicality of using the cross-power spectrum analyzer on the Space Shuttle to measure ionospheric parameters. Particular attention is given to investigating the integration time required to measure the cross-power spectral density to a desired accuracy.

Harker, K. J.↗

NASA NTRS1979

Laboratory simulation of ionospheric double-layers

A mechanism for double-layer formation in partially- or fully-ionized plasmas is described, founded on beam-plasma interaction: RF growth along the beam excites a rectified, ponderomotive electric field, which in turn causes charge separation. Laboratory studies of the mechanism are described.

Crawford, F. W.↗

NASA NTRS1978

Observations of a double-layer in a hot-cathode discharge

The meniscus region of a hot cathode discharge was selected for an analysis of the nonlinear interaction of a convectively amplifying wave with a background plasma. A potential step, resulting from rectification of the wave fields is observed, and it is noted that predicted values for the step are in good agreement with empirical data. Attention is given to the determination of plasma parameters (using a Langmuir probe placed in front of the cathode) in terms of their relation to the pondermotive force.

Levine, J. S.↗

NASA NTRS1973

Theory of a steady-state nonisothermal positive column in a magnetic field.

The steady state of a nonisothermal cylindrical discharge in a longitudinal magnetic field is described by three moment equations in the plasma approximation for electrons and ions. Volume generation of electron-ion pairs by single-stage ionization, the presence of axial current, and collisions with neutrals are considered. The theory yields radial profiles of the charged particle velocities, density, potential, electron and ion temperatures, and demonstrates similarity laws for the positive column. The results are compared with two-moment theories and with experimental data on helium, argon, and mercury vapor found in the literature for a wide range of pressures.

Ilic, D. B.↗

NASA NTRS1973

Low-frequency instabilities and plasma turbulence

A theoretical and experimental study is reported of steady-state and time-dependent characteristics of the positive column and the hollow cathode discharge (HCD). The steady state of a non-isothermal, cylindrical positive column in an axial magnetic field is described by three moment equations in the plasma approximation. Volume generation of electron-ion pairs by single-stage ionization, the presence of axial current, and collisions with neutrals are considered. The theory covers the range from the low pressure, collisionless regime to the intermediate pressure, collisional regime. It yields radial profiles of the charged particle velocities, density, potential, electron and ion temperatures, and demonstrates similarity laws for the positive column. The results are compared with two moment theories and with experimental data on He, Ar and Hg found in the literature for a wide range of pressures. A simple generalization of the isothermal theory for an infinitely long cylinder in an axial magnetic field to the case of a finite column with axial current flow is also demonstrated.

Ilic, D. B.↗

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.↗