Subpercent-Scale Control of 3D Low Modes of Targets Imploded in Direct-Drive Configuration on OMEGA

Multiple self-emission x-ray images are used to measure tomographically target modes 1, 2, and 3 up to the end of the target acceleration in direct-drive implosions on OMEGA. Results show that the modes consist of two components: the first varies linearly with the laser beam-energy balance and the second is static and results from physical effects including beam mistiming, mispointing, and uncertainty in beam energies. This is used to reduce the target low modes of low-adiabat implosions from 2.2% to 0.8% by adjusting the beam-energy balance to compensate these static modes.

Figure 1

(a) Comparison of the self-emission images recorded on the second capsule shot (upper figure) and the reference shot (lower figure). The black circles correspond to the inner edge contours of the intensity peak. The image timings are the addition of the timings of the strip and the timings inside the strip. The insert corresponds to the image recorded at 1.82 ns in the upper figure. (b) Evolution of the angular variation of the difference between the contour radius and the averaged contour radius [$\mathrm{\Delta }R(\alpha )$] for the images in the upper figure in (a). (c) Differences between the upper and the lower figures in (a) in the contour center positions for images at similar locations (i.e., recorded by the same pinhole) along $x$ [orange circles ($\mathrm{\Delta }{R}_{\mathrm{c}}{|}_x$)] and along $y$ [blue squares ($\mathrm{\Delta }{R}_{\mathrm{c}}{|}_y$)] as a function of the averaged contour radius [$⟨R(\alpha )⟩$ [37] ]; the $x$ and $y$ directions are indicated in (a). The error bars at the 90th percentile and the linear fits between 300 and $100\mu \mathrm{m}$ are plotted (dashed lines in corresponding colors).

Figure 2

(a) The four projections of the ablation surface determined at an average radius of $150\mu \mathrm{m}$ [$[R(\alpha ){]}_{150}$] are oriented perpendicular to the lines of sight of the corresponding framing cameras. The color bar shows the variation of the contour radii relative to $150\mu \mathrm{m}$. (b) The 3D motion of the ablation front surface center at an average radius of $150\mu \mathrm{m}$ (orange arrow) corresponds to the point that is at the minimum distance of the four green lines. The lines are defined by the lines of sight of each framing camera shifted by the measured projected motions of the ablation front surface [$(\mathrm{\Delta }{R}_{\mathrm{c}}{)}_{150}$]. The figures are drawn for the second capsule shot.

Figure 3

Difference in the target modes ($\mathrm{\Delta }{r}_l^m$) for (a) $l=1$, (b) $l=2$, and (c) $l=3$ of the ablation-front surface between shots 1 and 2 (orange points), 1 and 3 (blue points), and 2 and 3 (green points) as a function of the difference in the corresponding beam energy balance modes ($\mathrm{\Delta }{e}_l^m$). The linear fits (dashed black line) and the error bars are plotted.

Figure 4

(a) Comparison of the static target modes (open orange circles) with the target modes obtained for a balanced laser (solid orange circle) and optimized beam-energy balance (solid blue squares). Comparison of the target shape reconstructed adding modes $l=1$, 2, and 3 for a balanced laser (b) and optimized beam-energy balance (c).