Reduction of the deceleration phase to mitigate the negative effect of hydrodynamic instabilities in direct-drive ICF implosions

Abstract

In the deceleration phase of an Inertial Confinement Fusion capsule implosion Rayleigh-Taylor hydrodynamic instability can affect or even quench the ignition and thermonuclear burn wave propagation. This instability tends to mix the inner hot plasma with the cold and dense plasma shell providing a mixing layer where nuclear fusion reactions are inhibited. The 1D hydrodynamic code Multi-IFE has been used to simulate the implosion of a direct-drive high-gain laser-capsule design and the temporal evolution of the average radius and thickness of the mixing layer have been estimated. To mimic the effect of the reduced reaction rate the fuel reactivity in the mixing layer has been artificially set to zero thus inhibiting the burn wave propagation throughout it nullifying the energy gain. In order to overcome this negative effect is proposed the addition of secondary short and powerful laser pulse that would reduce the duration of the deceleration phase, which in turn get smaller the thickness of the mixing layer. A study has been performed to identify the optimal secondary laser pulse that allows recover the high energy gain.