Collective Effects in Three Pulse Cyclotron Echoes

Citation

Smith, Richard Ross (1972) Collective Effects in Three Pulse Cyclotron Echoes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PR88-HK58. https://resolver.caltech.edu/CaltechTHESIS:07122016-145602568

Abstract

Three-pulse cyclotron echoes, 3PE, in rare gas afterglow plasmas are investigated. The experiments are performed with the magnetic field parallel to the discharge tube, which passes perpendicularly through an S-band waveguide. The echo properties are experimentally shown to be incompatible with previous models.

Experiments on 3PE are performed, which show that the electron density is the most important parameter, especially for the growth and decay of the echo following the first two pulses. The density is shown to have a qualitative as well as quantitative effect on the echo. Periodic modulation of both the emission and absorption of the plasma is observed following the first two pulses, and these additional methods of investigating echo processes will be helpful in formulating a satisfactory theory.

A model containing the experimentally important parameters is developed, and it is based upon the relatively simple case of the generation of plasma waves following an impulsive excitation for times so small that the original transient response has lost negligible energy. Better agreement than with previous theories is obtained, especially in the qualitative dependence of the echo on the electron density. Electron velocity space instabilities are briefly examined and discarded as influences in echo experiments.

The detection and qualitative theoretical explanation of slow wave pulses created inside the plasma by the applied microwave pulses supports the mode conversion echo model.

Thesis Files