Structure of low-frequency helium glow discharge at atmospheric pressure between parallel plate dielectric electrodes

Atmospheric-pressure helium glow discharge at 100 kHz between parallel plate dielectric electrodes is studied experimentally and theoretically. Experimental work was carried out by spatiotemporal optical emission spectroscopy to examine the behavior of electrons. The emission from helium atoms revealed the behavior of high-energy electrons (above 22 eV), while the emission from the second positive band of nitrogen revealed the behavior of medium-energy electrons (11-20 eV). Theoretical work was carried out using a one-dimensional fluid model with local field approximation under the same discharge conditions as the experimental one. It was clarified that i) the discharge structure is essentially the same as that in low-pressure glow discharge, ii) ionization by secondary electrons from the cathode is essential for sustaining the discharge, and iii) ionization occurs at low electric field (about 30 Td). This last property is important for conducting `moderate' ionization for stable glow discharge at atmospheric pressure in the absence of localized discharge columns.