Capillary underwater discharges

In this paper, a capillary underwater discharge, that is sustained with direct current (dc) voltages up to 30 kV (20 mA), is investigated. In a capillary discharge scheme, the current is, at some point along its path between two submerged electrodes, flowing through a narrow elongated bore in a dielectric material. When the current density is sufficiently high, local boiling and subsequent vapor breakdown results in the formation of a plasma within this capillary. Spectroscopic measurements indicate that this kind of discharge is an efficient source of ultraviolet radiation (280-320 nm). Discharge images reveal that the plasma is initiated half way the capillary and that during plasma expansion, the anode and cathode plasma-liquid boundaries have markedly different velocities.