Hydrodynamic growth of shell modulations in the deceleration phase of spherical direct-drive implosions

The evolution of shell modulations was measured in targets with titanium-doped layers using differential imaging [B. Yaakobi , Phys. Plasmas 7, 3727 (2000)] near peak compression of direct-drive spherical implosions. Inner-shell modulations grow throughout the deceleration phase of the implosion due to the Rayleigh-Taylor instability with relative modulation levels of similar to20% at peak neutron production and similar to50% at peak compression (similar to100 ps later) in targets with 1-mm-diam, 20-mum-thick shells filled with 4 atm of (DHe)-He-3 gas. In addition, the shell modulations grow up to about 1.5 times due to Bell-Plesset convergent effects during the same period. At peak compression the inner part of the shell has a higher modulation level than other parts of the shell. (C) 2003 American Institute of Physics.