Multi-mode hydrodynamic evolution of perturbations seeded by isolated surface defects

Abstract

Inherently multi-mode evolution of isolated defects, such as straight grooves and axisymmetric dots on planar laser targets, is studied theoretically. The development of perturbations is considered for a propagating rippled shock front, a material interface subject to the classical Richtmyer–Meshkov instability (RMI), a rippled rarefaction wave produced by the feedout process, an ablation front subject to the ablative RMI, and a thin fluid layer subject to the classical Rayleigh–Taylor instability (RTI). For the small-amplitude regime, we have established specific characteristics of the perturbation evolution initiated with such defects, scaling, and conservation laws governing it. The main features of the nonlinear growth of the classical and ablative RTI starting from isolated defects are the lateral expansion of the bubbles and the oblique with respect to the direction of the acceleration, ejection of spikes. It results in filling up the void left from the bubble growth by the laterally converging spike material. This effect, first discovered in simulations by Dahlburg et al. [Phys. Fluids B 5, 571 (1993)], and very recently observed by Zulick et al. [Phys. Rev. Lett. 125, 055001 (2020)], is captured by the appropriate modification of the Ott–Basko thin-layer classical RTI theory for arbitrary defect profiles. Predictions for novel hydrodynamic experiments on multi-mode hydrodynamic perturbation evolution are presented.