[en] The x-ray driven ablation front hydrodynamic instability experiments at Nova span 1988-present, and can be divided into three generations. The 1st generation experiments consisted of planar foils with perturbations of the form k = k_x 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. The 2nd generation experiments investigated mode-mode interactions with imposed perturbations corresponding to the superposition of modes. They 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 pre-existing modes, coupled terms k_i ± k_j occur. The 3rd generation experiments focus on 3D Rayleigh-Taylor growth. They have recently done experiments with an imposed 3D single-mode perturbation of the form k = (k_x,k_y), with k_x = k_y. In the linear regime, this perturbation grows exponentially with wave vector k = (k_x² + k_y²)^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