Growth of pellet imperfections and laser imprint in direct drive inertial confinement fusion targets

Simple hydrodynamic models for describing the Richtmyer-Meshkov (RM) growth and the Rayleigh-Taylor (RT) instability are tested by simulation. The RM sharp boundary model predictions are compared with numerical simulations of targets with surface perturbations or stationary intensity perturbations. Agreement is found in the overall trends, but the specific behavior can be significantly different. RM growth of imprint from optically smoothed laser s is also simulated and quantified. The results are used to calculate surfa ce perturbations, growth factors, and laser imprint efficiencies. These in turn are used with standard RT growth formulas to predict perturbation grow th in multimode simulations of compression and acceleration of planar and s pherical targets. The largest differences between prediction and theory occ ur during ramp-up of the laser intensity, where RT formulas predict more gr owth than seen in the simulations. (C) 2001 American Institute of Physics.