A symmetric double-sided DBD arrangement with half-spherical, alumina-covered metal electrodes with a gap width of 1 mm was used. The alumina-covered electrodes had a diameter of about 4 mm and a tip radius of about 2 mm. The thickness of the dielectric above the tip was about 0.5 mm. The electrodes were placed in a vacuum tight glass cell. A custom-built sinusoidal high-voltage (HV) power supply (push-pull generator with HV transformer) generating up to 14 kV pp at 10 kHz frequency (f_rep) was used for the operation of the DBDs.