Quantifying the Effects of Scale and Illumination Geometry in Laser Direct Drive

The application of laser direct drive (LDD) research to ignition on the OMEGA laser depends on the degree to which implosions can be scaled in size (and energy) and use different beam geometries. In this talk we present an analysis of cryogenic experiments at two hydrodynamic scales ($S \quad =$ 0.8 and 1.0) [Ref. \footnote{ V. Gopalaswamy \textit{et al.}, Nature \textbf{565}, 581 (2019).}] and find that yield increases as $S^{\mathrm{4}}$ or faster after correcting for shot-to-shot sources of asymmetry (e.g., the laser pointing). These data also indicate a potential benefit in areal density (in excess of expectations) as targets become larger/thicker. This behavior could be due to changes in preheat or instability/mix (e.g., the capsule stalk) and will be discussed. We are also planning experiments that will quantify performance versus $\eta \quad = \quad R_{\mathrm{b}}$/$R_{\mathrm{t}}$, which is the ratio of the laser beam to target radius. The goal is to change the amplitude of the applied mode 10, which has been found to correlate with yield as $\eta^{\mathrm{2}}$ to $\eta^{\mathrm{3}}$ (Ref. \footnote{ A. Lees, ``Understanding the Fusion Yield and All of Its Dependencies Using Statistical Modeling of Experimental Data,'' to be presented at the 62nd Annual Meeting of the American Physical Society Division of Plasmas Physics, Memphis, TN, 9--13 November 2020.}). Lastly, we will connect this work to studies comparing spherical direct drive and polar direct drive,\footnote{ P. B. Radha \textit{et al.}, ``Polar-Drive Cryogenic Implosions on the OMEGA Laser,'' to be presented at the 62nd Annual Meeting of the American Physical Society Division of Plasmas Physics, Memphis, TN, 9--13 November 2020.}$^{\mathrm{,}}$\footnote{ W. Theobald \textit{et al.}, ``OMEGA Cryogenic Target Implosions in Polar-Direct-Drive Beam Geometry,'' to be presented at the 62nd Annual Meeting of the American Physical Society Division of Plasmas Physics, Memphis, TN, 9--13 November 2020.} and consider implications to LDD research on OMEGA and the National Ignition Facility.