Stability study of planar targets using standard and adiabat shaping pulses

The hydrodynamic stability of a planar target is considered for the conditions of the direct drive inertial confinement fusion. It has been recently proposed to reduce the ablative Rayleigh-Taylor instability growth by using the adiabat shaping in the ablation zone. In this work, we consider the relaxation adiabat shaping scheme [K. Anderson and R. Betti, Phys. Plasmas 11, 5 (2004); R. Betti, K. Anderson, J. P. Knauer, T. J. B. Collins, R. L. McCrory, P. W. McKenty, and S. Skupsky, Phys. Plasmas 12, 042703 (2005)]. In this scheme, a prepulse (“picket”) is followed by a relaxation period, when the laser is turned off. A parametric study of picket parameters is performed with a code dedicated to the linear stability analysis on the basis of spherical realistic simulations including full physics. The influence of the picket parameters is investigated numerically. Simulations show that the set picket/relaxation time mainly determines the target stability and that the adiabat shaping scheme modifies the perturbed state before the main acceleration. In particular, the perturbed density level is reduced in the cases studied. Finally, several planar configurations have been used to look into the details of perturbation growth. It has been found that stabilization increases with prepulse intensity at the beginning of the acceleration phase.