Studies on shock amplification, focussing and stability

Several devices for the amplification of plane shocks are proposed. The first, designed using Whitham's characteristics, is a 'shock nozzle', similar to Laval nozzles in steady flow; a minimum length variant, with finite deflections is also shown. A modification of the spiral contraction is then introduced, which avoids strong disturbances of the emerging shock. Experimental results validate the concepts put forward. The focussing of cylindrical shocks is then discussed, arguing that one cannot turn a plane shock into such a wave (even limited to an angle), by any two-dimensional configuration. Similarly, an (even partial) spherical implosion cannot be obtained from a plane shock, by any means. Finally, it is shown that, whereas fully circular or spherical implosions are unstable, stability is restored if the shock is confined by solid walls to a certain circular or solid angle, and a maximum value of about 35 degs is advanced.