Experimentally inferred dependencies of the fusion yield in direct-drive DT-layered ICF implosions

Aarne Lees, PhD Qualifying Exam, Advised by Professors Hussein Aluie and Riccardo Betti

Hopeman 224

In laser direct-drive inertial confinement fusion (ICF), focused laser light is used to implode a millimeter-size spherical shell layered with solid deuterium-tritium fuel (DT ice). Current direct-drive experiments at the OMEGA laser facility of LLE have achieved core conditions reaching about 70% of the values required for ignition by the Lawson criterion when hydrodynamically scaled to the laser energy available at the National Ignition Facility. The fusion yield is one of the most important performance metrics of ICF implosions therefore it is crucial to determine all its dependencies on design parameters. Even a combination of small improvements to aspects of current best-performing designs could lead to exceeding the hydroequivalent ignition threshold.

We use a method based on the statistical mapping model of [Gopalaswamy, V., et al. "Tripled yield in direct-drive laser fusion through statistical modelling." Nature 565.7741 (2019): 581-586.] to extract a number of subdominant dependencies of the fusion yield in a large database of ICF experiments at OMEGA. The yield degradation in experiments due to measured low-mode asymmetry signatures as well as buildup of helium from tritium beta-decay in targets is inferred and compared to simulations. A new implosion design is proposed to experimentally study the physics involved in the statistically inferred dependence of fusion yield on shock-timing and shell adiabat.