Measurement of a Richtmyer-Meshkov Instability at an Air-SF_{6} Interface in a Semiannular Shock Tube.

We report the first measurements of the perturbation amplitude in the converging Richtmyer-Meshkov instability in a semiannular shock tube. At early stages, the amplitude growth agrees well with the impulsive model considering the geometrical convergence effect. A quick decrease of the growth rate at late time, even to be negative, before the reshock is observed for the first time.