Record Pressures in OMEGA Cryogenic Direct-Drive Experiments via Subcooling

Achieving high pressures over 100 Gbar has been a long-standing objective for the cryogenic direct-drive fusion program. High pressures are challenging for ICF implosions as they require highly convergent implosions, which in typical cryogenic designs require a reduction in the fuel adiabat. In practice, the performance of low adiabat implosions fails to live up to theoretical expectations and has substantially lower hot-spot pressures, likely due to shock mistiming and the growth of hydrodynamic instabilities. We report on experiments that produce record inferred hot-spot pressures using cryogenic sub-cooling to reduce the vapor density within the cryogenic target, allowing the convergence ratio to increase independently from the adiabat. We describe also the two temperature, non-isobaric hotspot model used to reconstruct the pressure of implosion experiments from a number of neutron and x-ray diagnostics, and which has been benchmarked against simulations, and show that the pressures of subcooled implosions are increased substantially compared to standard implosions. We find also that the yields and areal densities of subcooled implosions are well predicted by statistical models trained only on standard cryogenic experiments, which suggests that the convergence ratio dependence of the statistical model accounts for the effect of hydrodynamic instabilities.