Experimental measurement of improved stability to achieve higher compression in ICF

A key objective toward achieving high gain in Inertial Confinement Fusion (ICF) is to achieve high compression. In recent indirect-drive capsule implosions on the National Ignition Facility (NIF), the SQ-n campaign is testing the hypothesis that reducing the hydrodynamic growth of perturbations is key to achieving higher compression of high-density carbon (HDC) based-ablators for ICF. The technique is designed around a 2-shock design, called BigFoot, tested on NIF in 2016 – 2019, which features good stability with the drawback of lower compression inherent to the intentional higher adiabat of this design. A “Scaling” and “Quality” importance of the implosion has led to a new campaign, called SQ-n, that is looking to reach higher compression using a ramped foot pulse shape to minimize early-time hydrodynamic instability growth and an optimized ablator dopant distribution. Three subsets of experiments were conducted within the SQ-n campaign to study the implosion symmetry, backscatter, stability, and compression. Keyhole experiments using VISAR enabled the development of a gently accelerating shock velocity as well as constraining models of foot drive and symmetry. The ice-ablator interface acceleration, important for managing the Richtmyer-Meshkov phase growth, was observed with Refraction Enhanced Radiography (RER) and the ablation front growth was measured using radiography of pre-imposed modulations. Finally, layered THD and DT implosions demonstrate higher compression has been achieved. Results of these experiments will be presented and discussed. LLNL-ABS-836109.