Feedout and Richtmyer-Meshkov instability at large density difference

The feedout process transfers mass perturbations from the rear to the front surface of a driven target, producing the seed for the Rayleigh-Taylor (RT ) instability growth. The feedout mechanism is investigated analytically an d numerically for the case of perturbation wavelength comparable to or less than the shock-compressed target thickness. The lateral mass flow in the t arget leads to oscillations of the initial mass nonuniformity before the re flected rippled rarefaction wave breaks out, which may result in RT bubbles produced at locations where the areal mass was initially higher. This proc ess is determined by the evolution of hydrodynamic perturbations in the rip pled rarefaction wave, which is not the same as the Richtmyer-Meshkov (RM) interfacial instability. An exact analytical formula is derived for the tim e-dependent mass variation in a rippled rarefaction wave, and explicit esti mates are given for the time of first phase reversal and frequency of the o scillations. The limiting transition from the case of RM perturbation growt h at large density difference (low ambient density behind the rear surface) to the case of feedout (zero density) is studied, and it is shown that the latter limit is approached only if the ambient density is extremely low, l ess than 1/1000 of the preshock target density. (C) 2001 American Institute of Physics.