RAYLEIGH-TAYLOR INSTABILITY EVOLUTION IN ABLATIVELY DRIVEN CYLINDRICAL IMPLOSIONS

The Rayleigh-Taylor instability is an important limitation in inertial confinement fusion capsule designs. Significant work both theoretical ly and experimentally has been done to demonstrate the stabilizing eff ects of material flow through the unstable region, The experimental ve rification has been done predominantly in planar geometry, Convergent geometry introduces effects not present in planar geometry such as she ll thickening and accelerationless growth of modal amplitudes (e.g., B ell-Plesset growth). Amplitude thresholds for the nonlinear regime are reduced, since the wavelength lambda of a mode m decreases with conve rgence lambda similar to R/m, where R is the radius. Convergent effect s have been investigated using an imploding cylinder driven by x-ray a blation on the NOVA laser [J. L. Emmet, W. F. Krupkel and J. B. Trenho lme, Sov, J, Quantum Electron. 13, 1 (1983)]. By doping sections of th e cylinder with opaque materials, in conjunction with x-ray backlighti ng, the growth and feedthrough of the perturbations from the ablation front to the inner surface of the cylinder for various initial modes a nd amplitudes from early time through stagnation was measured, Mode co upling of illumination asymmetries with material perturbations is obse rved, as well as phase reversal of the perturbations from near the abl ation front to the inner surface of the cylinder. Perturbation growth is observed due to convergence and compressibility alone, without the effects of acceleration, and scales as similar to 1/rho R, where rho i s the mass density, Imaging is performed with an x-ray pinhole camera coupled to a gated microchannel plate detector.