Volume mode excitation in submerged bubbles: Towards reducing breakdown voltage for plasma generation in liquids

Plasma ignition of submerged gas bubbles reduces the breakdown voltage required to introduce plasma into a liquid. It is possible to further reduce the breakdown voltage of bubbles in liquid water. Local enhancement of the electric field through bubble shape mode activation combined with volume modulation for decreased internal pressure and neutral density is a potential pathway for minimizing breakdown voltage. Although electrohydraulic control of bubble shape has been investigated^[1], for the purpose of reducing breakdown voltage, the quantitative benefits of accessing bubble volume modes remain unexplored. Submerged bubble volume modulation may be achieved by sonically or electrohydraulically driving a time-varying sinusoidal field at the Minnaert resonance frequency. Volume mode activation as a possible pathway to reduced breakdown voltage is demonstrated using Rayleigh-Plesset modeling of the transient bubble radius under an applied sinusoidal pressure signal. Results from an experimental investigation aimed at exciting volume modes are also presented. Additionally, results from preliminary experiments aimed at breaking down a volume mode oscillating bubble as a function of internal bubble pressure is presented. Here, a fast, low-light level photodiode is used to indicate breakdown.