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

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 crosssectional 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.

Optimal laser intensity profiles for a uniform target illumination in direct-drive inertial confinement fusion

A numerical method providing the optimal laser intensity profiles for a direct-drive inertial confinement fusion scheme has been developed. The method provides an alternative approach to phase-space optimization studies, which can prove computationally expensive. The method applies to a generic irradiation configuration characterized by an arbitrary number NBof laser beams provided that they irradiate the whole target surface, and thus goes beyond previous analyses limited to symmetric configurations. The calculated laser intensity profiles optimize the illumination of a spherical target.This paper focuses on description of the method, which uses two steps: first, the target irradiation is calculated for initial trial laser intensities, and then in a second step the optimal laser intensities are obtained by correcting the trial intensities using the calculated illumination. A limited number of example applications to direct drive on the Laser Mega Joule(LMJ) are described.