ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3aPAb2. Processes leading to cavity formation and dielectric breakdown in liquids subjected to high electric fields.

Hugh M. Jones

Dept. of Phys. and Eng. Phys., Stevens Inst. of Technol., Hoboken, NJ 07030

Erich E. Kunhardt

Stevens Inst. of Technol., Hoboken, NJ 07030

The use of liquid-filled gaps as acoustic sources requires an understanding of the contributions from various microscopic processes to the dynamics of current growth, cavity formation, and dielectric breakdown. A model is presented for the development of cavities and dielectric breakdown in liquids subjected to uniform high amplitude electric fields with durations of microseconds or less. In this model, breakdown proceeds in four stages: formation of a nucleation site in the liquid near an electrode, growth and expansion of this site until the local density is reduced sufficiently for electron-impact ionization to occur, growth of an electron avalanche and its transformation into an ionizing front, and propagation of the front via a sequence of processes occurring in the region ahead of the front, namely, heating by electron injection, lowering of the liquid density, and avalanche growth and retardation. Expressions for the duration of each of these stages are derived and their behavior with pressure and field strength analyzed. From this, a critical energy criterion for breakdown is obtained. Comparison is made with experimental results for water, salt solutions, and the liquid noble gases, and for pulse durations in the microsecond and submicrosecond time scales. [Work supported by ONR.]