Regular Article

Direct comparison of pulsed spark discharges in air and water by synchronized electrical and optical diagnostics

¹ Leibniz Institute for Plasma Science and Technology e.V. (INP Greifswald), Felix-Hausdorff-Straße 2, 17489 Greifswald, Germany
² Electrical Energy Systems Group, Department of Electrical Engineering, Eindhoven University Technology, 5600 MB Eindhoven, The Netherlands

^a e-mail: hans.hoeft@inp-greifswald.de

Received: 21 September 2018
Received in final form: 19 October 2018
Published online: 18 December 2018

Abstract

In this study, a direct comparison was made between pulsed spark discharges in air and water in sub-mm gaps. The discharges were ignited at atmospheric pressure in the same discharge arrangement for air and water, using a solid-state microsecond pulse source with ≈1 μs voltage rise time (U_max up to 37 kV). Fast voltage and current measurements were synchronized with iCCD imaging with high spatial resolution on symmetrical half-sphere tungsten electrodes (electrode gaps of up to 0.7 mm for air and 0.3 mm for water). The breakdown voltage and electrical field strength, maximal current, transferred charge, consumed electrical energy and discharge emission structure (e.g. discharge channel diameters) was obtained for all cases. Using the synchronization of the electrical data and the iCCD imaging, current and energy densities were estimated for the sparks in air and water. It was found that the breakdown voltage, the discharge current, the transferred charge, and the consumed electrical energy increase with the gap distance, and that this dependency is much stronger for discharges in water (compared to air). Due to the use of the same discharge arrangement and the same applied voltage, the difference in the discharge characteristics was directly quantified.