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AN INVESTIGATION OF NONLINEAR EFFECTS IN PLASMAS
STANFORD UNIV CALIF MICROWAVE LAB
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The motions of free electric charge carriers, as they exist in a plasma, are governed by nonlinear relationships between velocity and electric field intensity. The resulting spectral decay of propagating modes may, depending on boundary conditions and operating parameters, manifest itself in the form of nonlinear mixing, cumulative traveling-wave interaction, and parametric amplification. A theoretical and experimental investigation of this phenomenon, as it relates to the so-called plasmaguide configuration, is presented. The plasma employed in this study is furnished by the positive column of a low-pressure mercury vapor discharge. It is enclosed in an elongated glass tube which is surrounded by a slotted metallic sleeve. This geometry permits the propagation of electromechanical plasma modes, which are characterized by a low phase velocity and low dispersion for frequencies small compared with the plasma frequency. It is therefore possible to inject at the collector end of the tube two signals of different frequencies which, traveling at almost the same velocity, interact cumulatively over many wavelengths. This nonlinear interaction is studied by means of a sampling probe which moves along the waveguide slot. Author
APPROVED FOR PUBLIC RELEASE