Harmonic Generation and Parametric Oscillations in a Plasma

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Abstract
Nonlinear rf effects in plasmas are discussed in this paper. It is shown that the strong type of harmonic generation mechanism is due to the equation of motion for the plasma electrons being nonlinear, as is the relationship between current and velocity. A theory of plasma harmonic generators and parametric oscillators is given. Input reaction is taken into account and it is shown that a resonance at the output frequency tends to lead to high efficiency. Such a resonance is the electrostatic resonance of a plasma sphere. Experiments carried out with a small spherical rf discharge are described. A 25% conversion efficiency to the second harmonic of an S‐band signal has been obtained. Measurements have been made up to the seventh harmonic. For maximum efficiency a plasma resonance at the harmonic of interest is required. By tuning the system to be resonant at half the input frequency, parametric oscillations were obtained at this frequency, thus proving that the nonlinearity must be of a reactive type. It is believed this is the first time that parametric oscillations have been observed in a plasma.