Normal and Abnormal Glow Discharge Modes in Atmospheric Plasmas

Summary form only given. By the optical observation as well as electrical measurements, transition of the Townsend, normal glow, and abnormal glow discharge modes were observed in an atmospheric pressure RF plasma produced in the ambient air with helium or argon supply gas. The plasma was produced between the two plate electrodes up to about 1 cm apart with the powered electrode connected to a RF source and a dielectric plate covered the ground electrode. In the normal glow discharge mode, discharge sustaining voltage and current density showed almost constant value of 165 V and 13 mA/cm², respectively, and most of the applied RF power dissipated to enlarge plasma area. On the other hand, once the plasma covered the whole discharge area, the discharge voltage became larger as current increased. A distinctive difference between the two discharge modes was also observed in the measured phase angle between the discharge current and the applied voltage. During the normal glow discharge mode, increase of the input power brought about the phase angle change from 90deg to 50deg because of the plasma resistance drop by plasma area increase. In the abnormal glow mode, however, the phase angle augmented from 50deg to 60deg due to the plasma impedance change caused by shrink of the sheath width. The experimental results so far indicate that the discharge modes observed under the atmospheric pressure show basically same characteristics as those of low-pressure DC discharges