INVESTIGATION OF SHOCKWAVE PRODUCED BY LARGE VOLUME PULSED DISCHARGE UNDER WATER ∗ C.H. Zhang ξ , T. Namihira, T. Kiyan, K. Nakashima, S. Katsuki, H. Akiyama, H. Ito* and Y. Imaizumi* Dept. of Electrical & Computer Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan *RIX CO., 1321-10 Ueki, Sue-machi, Kasuya-gun, Fukuoka 811-2112, Japan ∗ This work was supported by 21 st Century COE program, and in part JSPS. ξ Email: zhang@eecs.kumamoto-u.ac.jp Abstract In this paper, the measurement and analysis of shockwaves generated by pulsed discharge in water are made with FUJI pressure measuring film. When pressure is applied, the reaction takes place between the color- forming material and color-developing material coated on the bases of the film, and color corresponding to the level of pressure is generated. Based on these results the energy transferred to the water and the average pressure of a shockwave are estimated. In addition, the electrical parameters and electrode configuration are optimized for maximum energy transformation efficiency into shock waves. I. INTRODUCTION As well known, shockwave can be produced by generation of a dense pulsed discharge plasma channel with underwater electrical wire explosion [1-3], which has been widely used for various scientific and technological purposes [4-8] such as demolition and drilling, hydro- acoustics and medicine (kidney stone destruction). In the past 50 years, all studies have shown a relatively low efficiency in transferring electrical energy stored in a capacitor into shockwave energy, because of a low resistance of the discharge channel at a low applied voltage and a small interelectrode gap [1]. Furthermore, various types of pressure probes were employed to determine the shockwave parameters [2,9,10]. However, none of them seems to be suitable for the purpose since the frequency range of the pressure waves lies between 10 7 and 10 9 Hz. In additional, these probes cannot be used for direct measurement for the pressure on the surface of the discharge plasma channels due to a possibility to be broken or damaged when a probe is closed to the discharge plasma channels. In this paper, strong shockwaves produced by pulsed discharge under water have been experimentally studied for the various operational conditions such as electrical parameters and electrode gaps. Moreover, measurement and analysis of pressures of strong shockwaves were performed by using FUJI pressure measuring film, FUJI PHOTO FILM CO., LTD, with a wide pressure ranging from 2.5 to 10 MPa. Finally, the electrical discharge parameters and electrode configuration are optimized for maximum energy transformation efficiency into shockwaves. II. EXPERIMENT AND DIAGNOSTICS The experimental set-up and some parameters of the circuit elements are presented in Fig.1. A Marx generator was used for a high-voltage pulsed power source in our study. These capacitors connected in parallel were charged to a negative high voltage, and triggered by an external signal to a gap switch. The inductors, instead of the conventional charging resistors, are used to reduce the energy losses during the charge, thus the overall efficiency is improved. The electrode system is a couple of copper wires with the diameter of 5 mm, which is immersed in technical water. The electrode gap was changed from 10 mm to 50 mm Conditions C d :0.8 /0.22µF 40 kV L : 100 µH R d : 1 Ω R c : 150 Ω C t : 0.5 nF Fig.1 The experimental set-up