Modes of Impulse Barrier Discharge to Water Surface in Atmospheric Air

The possibilities of creating a homogeneous discharge in air of atmospheric pressure between a flat metallic electrode covered by a dielectric barrier and water surface are demonstrated. In the experiments, the discharge was initiated in the gas gaps by applying unipolar voltage pulses with fronts of ~15 ns and duration of ~100 ns. It was found that the discharge mode was affected by the pulse repetition rate. Its critical magnitude corresponding to the appearance of a homogeneous discharge was reduced from 500 to 50 s -1 if the length of the air gap was increased from 1 to 4 mm. The lifetime of a homogeneous discharge mode was affected by the total duration of the discharge. Thus, it was about several tens of seconds at a pulse repetition frequency of 100 s -1 and it reduced at increased frequencies. It is suggested that the transition from homogeneous to inhomogeneous modes is associated with local overheating of the gas due to significant energy dissipation in the discharge volume.