Observation of Electron Density Oscillations in Confined Plasma with Two Radio-Frequency Capacitive Sheath

Summary form only given. The spatial electron density oscillation in a symmetric, two radio-frequencies, 27.12 MHz and 1.937 MHz, confined- capacitive-coupled discharge has been measured using a floating hairpin resonance probe. By measuring ne in a space and phase-resolved manner, we observe oscillations of bulk electron density at both (1.937 MHz and 27.12 MHz) drive frequencies. With the probe placed within the region of the maximum low-frequency sheath extent, the expulsion of the electrons by the large low-frequency voltage is observed. When the probe is placed in the opposing sheath, the phase of the electron expulsion is shifted by half-cycle as expected. Near the mid-plane of the parallel plate electrodes, the plasma density oscillates twice per low-frequency cycle. The observed electron density oscillations are attributed to the expansion and the collapse of the radio-frequency sheaths, resulting in the spatial electron density variation between the discharge electrodes. The 27.12 MHz oscillation in electron density is observed to be higher in magnitude during the phase when 1.937 MHz sheath voltage has maximum in amplitude.