Abstract
Keywords
1. Introduction
The goal of inertial confinement fusion (ICF)[
The experimental configuration is described in Section
2. Experimental configuration
Figure
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The experiments were conducted with laser drives and conditions similar to those used in high-compression layered DT implosions (with ‘low-foot’ drive)[
The experiments were driven by a temporally shaped, 21-ns long laser pulse with a peak power of and a total laser energy of 1.3 MJ (shown in Figure
3. Experimental images
Figures
by showing the OD Fourier spectrum of the signal plus noise (from the image in Figure
4. Simulated images
The experiments were modeled using the same methodology as the 3D simulations described in Ref. [
Figure
5. Discussion
In the high-compression experiments performed during the NIC[
Recent HGR experiments directly measured the growth factors of large-amplitude 2D pre-imposed modulations at the ablation front[
Another recent hypothesis suggested that increased levels of oxygen contamination in the bulk of the capsule, together with oxygen spatial nonuniformities, could significantly increase the modulation growth[
In addition, x-ray radiography experiments using the same (‘native’) surface roughness as typically used in the capsules for layered DT implosion are being planned, following the first experiments described in this paper. Some other possible seeds for instability growth, such as radiation asymmetry[
6. Conclusions
Hydrodynamic instability growth of 3D surface-roughness modulations was studied in spherical implosions at the NIF. The initial amplitudes were increased by a factor of four, compared with standard specifications, in order to increase the signal-to-noise ratio and to qualify a technique for measuring 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. The measured modulation levels at a capsule convergence ratio of , representing most of the acceleration phase, were times larger than the simulated levels. Several hypotheses were discussed to explain the results, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard or ‘native-roughness’ capsules identical to those used in layered DT implosions as well as experiments with deliberately imposed oxygen spatial modulations.
References
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