Electron density in surface barrier discharge emerging at argon/water interface: quantification for streamers and leaders

Optical emission spectroscopy, fast intensified CCD imaging and electrical measurements were applied to investigate the basic plasma parameters of surface barrier discharge emerging from a conductive water electrode. The discharge was generated at the triple-line interface of atmospheric pressure argon gas and conductive water solution at the fused silica dielectrics using a sinusoidal high-voltage waveform. The spectroscopic methods of atomic line broadening and molecular spectroscopy were used to determine the electron densities and the gas temperature in the active plasma. These parameters were obtained for both applied voltage polarities and resolved spatially. Two different spectral signatures were identified in the spatially resolved spectra resulting in electron densities differing by two orders of magnitude. It is shown that two discharge mechanisms take a place: the streamer and the leader one, with electron densities of 10¹⁴ and 10¹⁶ cm⁻³, respectively. This spectroscopic evidence is supported by the combined diagnostics of electrical current measurements and phase-resolved intensified CCD camera imaging. (paper)