NIF Invited: How numerical simulations helped to achieve breakeven in inertial confinement fusion implosions at the National Ignition Facility*

The inertial confinement fusion program relies upon detailed simulations with radiation hydrodynamic codes to design targets and to interpret the experimental results. The simulations treat as much physics from essential principles as is practical, including laser deposition, cross beam energy transfer, x-ray production and transport, NLTE kinetics, thermal transport, hydrodynamic instabilities, thermonuclear burn, and transport of reaction products. Vast increases in computing power, combined with computer code improvements, have enabled 3D simulations that treat all known asymmetry sources. High resolution full sphere capsule simulations performed with HYDRA assessed how various asymmetry sources were limiting the performance of cryogenic capsule implosions on the NIF. These included engineered features, isolated defects and roughness on capsule surfaces, ablator grain structure and low mode drive asymmetries. These simulations indicated that a combination of several asymmetry sources were limiting performance and that a more robust design was essential to overcome them. Simulations, assisted by data driven models, were used to optimize the target designs, also making use of increased laser energy, to give them greater robustness against the perturbations. Preshot predictions of the first experiment that surpassed breakeven yielded thermonuclear burn conditions that matched the experimental results reasonably well, with a target gain of ~1.5. We will cover the key developments in radiation hydrodynamic codes and modelling methodologies that enabled these simulations.