Potential structure of discharge plasma inside liquid directly measured by an electrostatic probe

Potential structures of a discharge plasma inside a liquid are investigated by an electrostatic probe measurement. The time evolution of radial profiles of the floating potential for the plasma inside liquid reveals that the dominant negative charges in the plasma are the negative ion species such as OH ^- and O₂^- rather than electrons. In addition, a positive potential gradient exists at the plasma-liquid interface due to the presence of an electrical double layer which is caused by the separation of low-mass positive ion of H⁺ and high-mass negative ions of OH ^- and O₂^- near the plasma-liquid interface.