Hydrodynamical instabilities in ablatively driven multilayer targets

When two fluids of different densities are in contact with each other and their interface is accelerated in some way, a wide variety of fluid motions nay occur. When a heavy fluid is resting on top of a light fluid in a gravitational field (or any type of constant force field), the interface separating the two fluids is unstable with perturbations initially growing exponentially in time. This instability is commonly referred to as Rayleigh-Taylor (RT) instability after its discoverers. In contrast, if the interface separating the two fluids is impulsively accelerated (say by a shock wave), the interface again goes unstable and the resulting instability is referred to as Richtmyer-Meshkov (RM) instability. Moreover, due to shearing at the interface Kelvin-Helmoltz (KH) instability develops. In the nonlinear stage the fluid interface is found to develop structures having finger like shapes. The structure resembles a bubble (spike) according as a lighter (heavier) fluid pushes into a heavier (lighter) fluid. The dynamics of interfacial instabilities have been studied for several cases. These types of instabilities find their applications in inertial confinement fusion (ICF) experiments where the target of small hollow spherical pallet is bombarded with very powerful lasers from all around which requires to be mitigated for efficient compression. These instabilities have also wide applications in Astrophysical phenomena like supernova explosion, crab nebula, etc. (author)