Observation of the development of pulsed discharge inside a bubble under water using ICCD cameras

Abstract

The development of discharge inside a bubble in water is observed using high-speed gated ICCD cameras. A tungsten wire is inserted into a glass tube, which is immersed in water. Argon gas is injected into the glass tube through a solenoid valve to generate bubbles at the tip of the glass tube. The pulsed high voltage is generated using an inductive energy storage system pulsed power generator driven by a SI-thyristor. Two ICCD cameras with optical axes perpendicular to each other are used to take two orthogonal images, and an ICCD camera that is capable of taking 12 consecutive photographs used to evaluate the propagation velocity of the discharge. The discharge propagates into the bubble from the tip of the wire in the glass tube. Then, the discharge propagates along the bubble surface. The propagation velocity is almost independent of water conductivity and 2.7–3.6 × 105 m/s. The average maximum length of the discharge propagation decreases from approximately 8.9 to 5.4 mm with increasing water conductivity from 7 to 1000 μS/cm. Indigo carmine, a commonly used organic dye, was used as the chemical probe of the active species produced by the discharge inside the bubble. The amounts of indigo carmine decomposition with 120 min of treatment is 0.24–0.26 μmol and independent of water conductivity. Meanwhile, the energy efficiency for the indigo carmine decomposition in water decreases from 18 to 7.3 μmol/Wh with increasing water conductivity from 7 to 1000 μS/cm. The amount of hydrogen peroxide production by the treatment increases from 2.0 to 3.1 μmol with increasing the conductivity. These results show that the amount of active species consumed in loss reactions such as their recombination increases with decreasing length of discharge propagation.