Experimental study of capacitive He/O2 discharges at atmospheric pressure

Electrical and optical measurements of capacitively-coupled RF (13.56 MHz) He/O-2 discharges at atmospheric pressure were carried out by changing the discharge gap length from 0.6 to 2.0 mm. The addition of oxygen to the He discharges varied from 0 to 4%. A distinct change in the dependence of the dissipated power on discharge voltage can be induced in any conditions. The voltage when the change occurs increases monotonically with an increase in oxygen content as well as gap length. The intensity of the 845 nm line emitted from excited oxygen atoms, which is normalized by the intensity of the 750.4 nm line emitted from excited Ar and the ratio of the ground state Ar density to the total density of neutral species. is investigated as a function of the dissipated power, whereas the ozone concentration is detected by the optical absorption at 254 nm. The normalized intensity is approximately proportional to the dissipated power, whereas the ozone density decreases as the power increases.