ABSTRACT
This chapter discusses the well-established classical plasma discharge physics in gas phase to introduce some background knowledge. It describes a theoretical framework for understanding the propagation of streamers of electric discharge in water subjected to high voltage. The gas channels can be formed through the development and electric expansion of gas bubbles already existing in water or by additional formation of the vapor channel through fast local heating and evaporation. The surface tension tends to minimize the surface area and subsequently stabilize the disturbance, while the local enhancement of the electrostatic force tends to push the disturbance to grow. As the voltage continues to increase, the instability enters the electrostatic mode, where the electrostatic force exceeds the force created by the surface tension and becomes the dominant force. Polarity differences in hold-off voltages and breakdown initiation times are in agreement with the microbubble models.
