Ablation front hydrodynamic instability experiments on Nova

Summary form only given, as follows. Our X-ray driven ablation front hydrodynamic instability experiments at Nova span 1988-present, and can be divided into three "generations". Our 1st generation experiments consisted of planar foils with perturbations of the form k=k/sub x/ (1D wave vector) imposed on the drive side of the foil. A variety of drive pulse shapes, foil materials, and perturbation wavelengths and amplitudes were investigated, with growth factors of up to 80 being observed. Our 2nd generation experiments investigated mode-mode interactions with imposed perturbations corresponding to the superposition of modes, k=/spl Sigma/k/sub xi/spl circ//. We have done experiments with two-mode and eight-mode foils. In the linear regime, the modes grow independently with their own respective growth rates. In the nonlinear regime, in addition to the higher harmonics of the preexisting modes, coupled terms k/sub i//spl plusmn/k/sub j/ occur. Our 3rd generation experiments focus on 3D Rayleigh-Taylor growth. We have recently done experiments with an imposed 3D single-mode perturbation of the form k=(k/sub x/,k/sub y/), with k/sub x/=k/sub y/. In the linear regime, this perturbation grows exponentially with wave vector k=(k/sub x//sup 2/+k/sub y//sup 2/)/sup 1/2/ In the nonlinear regime, the perturbations evolve into broad bubbles surrounded on four corners by very dense, localized spikes with "archways" or saddle points in between. Simulations suggest that this 3D square mode grows larger than the corresponding 2D perturbation with the same magnitude wavevector and initial amplitude.