Analysis of three-dimensional effects in laser driven thin-shell capsule implosions

Abstract

Three-dimensional (3D) hydrodynamic numerical simulations of laser driven thin-shell gas-filled microballoons have been carried out using the computer code MULTI-3D [Ramis et al., Phys. Plasmas 21, 082710 (2014)]. The studied configuration corresponds to experiments carried at the ORION laser facility [Hopps et al., Plasma Phys. Controlled Fusion 57, 064002 (2015)]. The MULTI-3D code solves single-temperature hydrodynamics, electron heat transport, and 3D ray tracing with inverse bremsstrahlung absorption on unstructured Lagrangian grids. Special emphasis has been placed on the genuine 3D effects that are inaccessible to calculations using simplified 1D or 2D geometries. These include the consequences of (i) a finite number of laser beams (10 in the experimental campaign), (ii) intensity irregularities in the beam cross-sectional profiles, (iii) laser beam misalignments, and (iv) power imbalance between beams. The consequences of these imperfections have been quantified by post-processing the numerical results in terms of capsule nonuniformities (synthetic emission and absorption images) and implosion efficiency (convergence ratio and neutron yield). Statistical analysis of these outcomes allows determination of the laser tolerances that guarantee a given level of target performance.