Observation of free-streaming electrons in plasmas

Abstract
The excitation and propagation of electron waves in a plasma have been studied experimentally in a low‐density and large‐volume plasma. For frequencies larger than the electron Langmuir frequency, an electron plasma wave was observed which is predicted by the linear theory for a Maxwellian plasma. For smaller frequencies, free‐streaming electron or ballistic signals are observed. For frequencies close to the electron Langmuir frequency, both the electron plasma wave and the free‐streaming electron are excited and show interference patterns. These observations are compared with the theoretical predictions. The effect of a sheath formed around a transmitter on the free‐streaming electron is also discussed.
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