Parametric Excitation of Electron Plasma Oscillations

Nonlinear phenomena in parametric resonances of electron plasma oscillations predicted and partially found out in previous papers (J. Phys. Soc. Japan 30 (1971) 309 and Rep. Fac. Sci. Shizuoka Univ. 5 (1970) 9) are investigated. A frequency of externally applied electric field f ex swept automatically near twice the plasma frequency 2 f pe and an amplitude of oscillations excited with resonance frequency f r ≃ f pe are displayed on the X - and Y -axes of a monitor scope, respectively. Threshold values of pumping voltage V 0 for the parametric excitation of the oscillation and nonlinear shift of the resonance frequency due to the input voltage V in were measured, and the asymmetrical hysteresis curve of the excited oscillation amplitude for increasing and decreasing f ex was easily observed by convenient method in which the detection frequency f r was swept by a servomotor. Parameters including a collision frequency and an electron density gradient are also determined from experimental data.