Progress towards hydro-equivalent ignition in OMEGA direct-drive DT-layered implosions*

Advancements in experimental techniques and data-driven modeling have resulted in considerable progress in DT-layered implosion experiments on the OMEGA laser, bringing the possibility of thermonuclear ignition in direct-drive configurations with megajoule-class lasers closer to reality. Statistical modeling is applied to every cryogenic implosion to infer various degradation mechanisms such as preheat, engineering features, and vapor pressure. Dedicated focused-physics implosions were performed, scanning a single parameter to experimentally observe and quantify the impact of each of these challenges on energy coupling and hydrodynamic stability. These studies include subscale implosions with bilayer targets where it was shown that Si dopants increase the threshold for the two-plasmon-decay instability, enabling greater intensities to be delivered on target without significant fast-electron preheat. Engineering features were studied by varying the glue spot and stalk sizes, providing bounds on the maximum allowable size of such features. Finally, vapor pressure was explored through cryogenic subcooling, demonstrating greater areal densities through increased convergence while maintaining yield. Based on these results and statistical predictions, yield and areal density have been optimized to produce unprecedented performance on OMEGA. Recent implosions have achieved core conditions that extrapolate to a burning plasma when hydrodynamically scaled to 2 MJ of symmetric laser illumination. Using high implosion velocities (>450 km/s) and moderately high adiabats (~5), these experiments produced record-high scaled Lawson parameters equal to 86 ± 2% of that required for ignition with expected yields of up to 1.5 ± 0.2 MJ. Work is ongoing to push performance even higher using novel experimental designs and live feedback from machine-learning models, presenting a viable route toward hydro-equivalent ignition on OMEGA.