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

A novel method for generation of focused shock waves based on multi-channel partial electrical discharges in water with an increased conductivity has been developed. The multi-channel discharge is formed on a composite anode consisting of a metallic electrode covered by a thin porous ceramic layer. Two versions of the generators have been realized. In the first one a cylindrical pressure wave is created on a cylindrical anode 60 mm in diameter and 100 mm long. At the applied voltage of 30 kV, a large number of short discharge channels distributed almost homogeneously on the anode surface are initiated. Each channel creates a semi-spherical pressure wave, and by superposition of all of the waves a cylindrical pressure wave propagating from the anode is formed. The cylindrical pressure wave is focused by a metallic parabolic reflector (cathode) and near the focus it is transformed to a strong shock wave. In the second version a convergent spherical pressure wave is formed by the same kind of the multi-channel discharge on a composite anode in the form of a part of spherical cavity. The discharge volume with the conductive water solution is separated from the experimental space (distilled water) by an acoustically transparent membrane. When supplying the discharges by 1 /spl mu/F condenser bank charged to 30 kV, the amplitude of the shock wave reached 100 MPa at the focal point for the both generators. The shock waves are sharply focused to a focal area of 3 mm, in diameter transversally (full width at a half maximum) and of 40 mm longitudinally. Interaction of two shock waves generated by two subsequent discharges has been demonstrated. Cellular damage induced by the shock waves was demonstrated on hemolysis of human erythrocytes and on damage of lymphocytes.