The Effect of Nonuniformity Growth on Direct-Drive Plastic-Shell Implosions on the OMEGA Laser

The in-flight aspect ratio (IFAR)---the ratio of the shell radius to its thickness---is an important implosion parameter that defines the minimum energy required for ignition and characterizes nonuniformity growth. Target performance is systematically studied in deuterium-filled warm plastic-shell implosions using triple-picket laser pulses on the OMEGA Laser. Picket energies and the timing between the pickets are systematically varied to obtain IFAR's between 30 and 60. Observed yields increase by nearly a factor of 3 when the IFAR is reduced to 30 from 60. A nearly 1-D value of areal density, $\langle $\textit{$\rho $R}$\rangle \quad \sim $ 170~mg/cm$^{2}$, is observed for IFAR $\sim $ 30. Observed $\langle $\textit{$\rho $R}$\rangle $ is significantly reduced from 1-D values for IFAR $\sim $ 60, with a value $\sim $140 mg/cm$^{2}$. These observations demonstrate the scaling of direct-drive target performance with IFAR. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.