Visualization and analysis of underwater shock wave focusing generated by magnetic pulse compression circuit (MPC)

Abstract

Recently, shock waves have been attractive with rising attention in medical field. Extracorporeal Shock Wave Lithotripters (ESWL) has been one of its very successful applications. However, the effects of shock waves on living tissue are not understood sufficiently, because there are lots of unknown points about shock wave interaction. In order to study shock waves effect, pulsed electric discharges produced by magnetic pulse compression (MPC) were used to generate underwater shock waves. The water was degassed by a vacuum pump, in order to eliminate the influence of dissolved air. Saline electrolyte was used in order to take impedance matching. The diameter of the reflector was 20 mm. We used shadowgraph method for the observation of shock waves. Two shock waves were observed, one by expansion of plasma, and another by collapse of a cavitation bubble. The shock waves are focused by using an ellipsoidal reflector. The shock wave generate at the 1st focal point of ellipsoidal reflector, focused at the 2nd focal point. The paper investigates the formation and behavior of underwater shock wave and bubble generated by ellipsoidal reflector. After shock wave formation and propagation at the 1st focal point, at first a spherical diverging shockwave (SDSW) was observed, then a converging shock wave (CSW), followed by shock wave focusing at the 2nd focal spot. By using high speed visualization and image analysis, the velocity and pressure of shock waves were evaluated.