Plasma Resonance in a Radio-Frequency Probe

When the frequency of a low-voltage r-f signal superposed on a probe was swept within an adequate frequency range, the d-c component of the electron current due to the nonlinearity of the sheath impedance was measured. lt was found that a resonant increase appeared in the current at the electron plasma frequency, omega /sub p/ = (4 pi N/sub 0/e/sup 2/m)/sup 1/2/, wh ere N/sub 0/ is electron density. The relation between the frequency of r-f voltage and the corresponding d-c component of the electron current to the probe is shown. The height of the resonance peak depended not only on the magnitude of the voltage, but on the collision frequency of electrons with atoms. (M.C.G.)