Electrical discharge in gas bubbles in gel

The development of electrical discharge in gas bubbles immersed in a liquid or a gel depends on the combination of the conductivity and dielectric properties of the medium as well as on the composition of the gas in the bubbles. The interest in a discharge in hydrogels is strongly stimulated by its use in combination with plasma in biology and medicine. Here, we use the electrical measurements of the current waveform and fast imaging and demonstrate the correlation between the discharge propagation in the bubble and the time evolution of the discharge current. We demonstrate experimentally that, if the dielectric constant is low and the conductivity is high (short time constant), then the discharge continues to propagate and to increase in brightness and the current continues to grow until the applied voltage is removed. The quenching of the discharge typical for dielectric barrier discharge is not observed and the effects are similar in hydrogels and in water. A simple circuit model is used to explore the dependence of the current waveform on the parameters of the medium and plasma. The shape of the current pulse significantly affects the amount of energy produced by the discharge and hence is an important property for the design and monitoring of plasma sources used for water decontamination and for plasma activation of gels.