Shock-ignition targets: Effects of low-to-intermediate mode implosion asymmetries *

In inertial fusion shock-ignition schemes [1,2], generation of the required central hot spot is "assisted" by a strong converging shock-wave, driven by a final laser spike. This process differs from hot spot formation in the conventional ignition scheme. In particular, interaction of shock waves in the nearly stagnating fuel affects both sensitvity to implosion asymmetries and growth of deceleration-phase Rayleigh-Taylor instability. To address these issues, we perform 2D numerical simulations of targets consisting of a cryogenic DT layer and a plastic ablator. We consider both single-mode and multi-mode perturbations of the velocity field (with mode numbers l in the range 1-12). We study yield degradation as a function of perturbation mode and perturbation amplitude, for different values of laser compression power, laser spike power, and DT vapour density. The relation between sensitivity to drive asymmetries and ignition threshold factors computed with 1D simulations is also discussed.

[1] R. Betti et al., Phys. Rev. Lett. 98, 155001 (2007).

[2] S. Atzeni et al., Nucl. Fusion 54, 054008 (2014).