Electron properties of radio-frequency capacitive discharge at atmospheric pressure

Along with the low temperature plasmas operated at low pressure, the information on electrons is particularly valuable and indispensable in elucidating unrevealed discharge mechanisms and various physical phenomena occurring in atmospheric pressure plasmas. Due to the limited availability of simple electron diagnostics for atmospheric pressure plasmas, discharge properties were studied using theoretical models with relevant approximations. In this presentation, we report a simple electron density (n_e) and temperature (T_e) diagnostics with high temporal and spatial resolution based on neutral bremsstrahlung due to the electron and neutral atom interaction in the ultraviolet and visible range emitted from atmospheric pressure plasmas. For an argon radio-frequency capacitive discharge, we investigated the electron properties under various plasma conditions. Capacitive discharges in argon and helium show different continuum spectra, and we notice that driving frequency plays an important role in the electron properties. Time-resolved emission spectra and the corresponding n_e and T_e during one rf cycle of the argon capacitive discharge were obtained. The result showed that T_e varied from 2.3 eV to 3.0 eV while electron density did not change significantly. Furthermore, a simple diagnostics for two-dimensional distribution of time-averaged T_e using a commercial digital camera with optical filters is presented.