Abstract
The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility (NIF) implosion experiments. The effects of the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L = 24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations. It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase. The later flow field not only shows large areal density P2 asymmetry in the main fuel, but also generates large-amplitude spikes and bubbles. In the deceleration phase, the increasing mode coupling generates more new modes, and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions. The combination of the low-mode and high-mode perturbations breaks up the capsule shell, resulting in a significant reduction of the hot spot temperature and implosion performance.
Highlights
In the indirect-drive inertial confinement fusion (ICF) [1e3], the laser energy is converted to the thermal X-ray in a high-Z hohlraum
The low-mode asymmetries can result in significant distortions of the hot spot and capsule shell shape which have been observed in the National Ignition Facility (NIF) implosion experiments [4,14e17]
When both the low-mode radiation flux asymmetry and intermediate-mode capsule surface roughness are imposed on the capsule during the implosion, the long-wavelength perturbation imprinted from the drive asymmetry will interact with the perturbed surface, and generate new modes by the mode-coupling effects
Summary
In the indirect-drive inertial confinement fusion (ICF) [1e3], the laser energy is converted to the thermal X-ray in a high-Z hohlraum. The recent 3D post-shot simulations of the NIF ignition implosions have considered the radiation flux asymmetries and capsule surface roughnesses, while included the tent defect by the surrogate perturbations. This 3D work focused on the comparison between simulations and experiments, while the effects of model coupling were not studied [5]. We will perform the 2D ignition capsule implosion simulation with both the low-mode radiation flux asymmetry and the intermediate-mode capsule surface roughness, and the effects of the mode-coupling on the perturbation growth and implosion performance will be investigated for the first time.
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