Stability criteria for converging shock waves

Two simple analytical criteria are presented to determine approximately the region of (form and radial) stability for converging (shock) waves as function of the perturbation parameters amplitude Δr/R and center angle γ. By comparison with computer calculations these criteria were found to be safe approximations. The criteria may be stated using an index of refraction N = Vsub(infinity)/V(r) for the wave front. (author)