Evolution of Helium DBD at Atmospheric Pressure

Summary form only given. Dielectric barrier discharge (DBD) of helium at atmospheric pressure was experimentally investigated. The discharge device was powered by a high voltage AC source with a frequency varying from 20 kHz to 50 kHz. Two parallel-plane electrodes are 50 mm in diameter. One electrode was made from aluminium and the other from ITO (indium tin oxide) film that is transparent for taking discharge picture end-on. Both electrodes were covered by one quartz plate which is 120 mm times 120 mm in size and 1 mm in thickness. The gas gap was kept at 5 mm. The applied voltage was measured with a capacitive divider VD305A from Pearson Electronics and the discharge current was obtained by using a current-viewing resistor of 50 ohm. For plotting Lissajous figures, the transported charges during discharge were measured with a capacitor connected in between the ITO electrode and the ground. The evolution of discharge pattern was taken end-on and side-on with an intensified CCD camera (PIMAX2: 1003RB-FG-43 from Princeton Instruments). The time-resolved spectrum from discharge was recorded with a spectrometer (SP-2558 from Acton) coupled to the ICCD camera. The transition from a homogenous glow discharge to a filamentary discharge was observed with the help of fast gated ICCD (exposure time of 10 ns) as the applied voltage or air additive was increased. The roles of He metastable atoms play in getting a homogeneous glow discharge were discussed.