Generation of focused shock waves by multi-channel discharges in water

A novel method for generation of focused shock waves in water has been developed. A cylindrical pressure wave created by a high voltage multi-channel discharge in water with an increased electrical conductivity is focused by a metallic parabolic reflector. The discharge is formed on a composite anode consisting of a cylindrical metallic electrode covered by a thin porous ceramic layer. In such arrangement the electric field on the anode reaches almost the value of E = U/d/sub c/, where U is the applied voltage and d/sub c/ is the thickness of the layer. For U = 30 kV and d/sub c/ = 0,3mm the electric field is of the order of 1 MV/cm that results in initiation of a large number of short discharge channels distributed almost homogeneously on the anode surface. Each channel creates a semi-spherical pressure wave, and by superposition of all of the waves a cylindrical wave is formed. Schlieren photography was used for visualization of the pressure field and the waveforms of the shock waves were measured by pressure sensors. When supplying the discharge by 1 /spl mu/F condenser bank charged to 30 kV, the amplitude of the shock wave reached 100 MPa at the focal point. A propagation of two shock waves generated by two subsequent discharges has been demonstrated. Preliminary experiments on interaction of the shock wave with biological objects have been done.