Search

We investigate herein how long-wavelength perturbations affect the nonlinear evolution of the multimode ablative Rayleigh–Taylor instability (ARTI). A single-mode ARTI with an initial small amplitude is first investigated to validate the reliability of the proposed simulation code. The results show that both linear growth rates and asymptotic bubble velocities obtained from simulations are in reasonable agreement with theoretical results. Initial perturbations with different long-wavelength perturbations are compared to investigate the contribution of the long-wavelength perturbations to the nonlinear evolution of the ARTI mixing. Beyond the nonlinear saturation limit [S. W. Haan, Phys. Rev. A 39, 5812 (1989)], the long-wavelength perturbation promotes the ARTI mixing and facilitates the development of the large-scale structure on the ablation surface. In the self-similar analysis, the simulation results indicate that the self-similar growth parameters decrease with increasing initial longest-wavelength modes. [ABSTRACT FROM AUTHOR]

In traditional indirect-drive double-shell inertial confinement fusion, high-energy x-ray preheat has always been identified as a major source of degrading implosion performance. However, a significant increase of the neutron yield is observed in ignition-like double-shell implosion experiments performed at Shenguang laser facility by intentionally utilizing high-energy x-ray preheat, mostly from the M-band. Permission of more M-band x-ray absorption inside the inner shell can both significantly mitigate the mix between the fuel and shell with a more stable Awtood number at the fuel-shell interface during the shell deceleration and slightly improve the symmetry of the imploding shell with a high entropy state of the shell, and the contribution outweighs the potential detriment to destabilizing the inner shell from the M-band preheat, which is consistent with radiation-hydrodynamics simulations and theoretical analysis. This novel understanding of the favorable impact of high-energy x-ray preheat on double-shell implosion could facilitate to achieve volumetric ignition and burn with high-Z shells.

X-ray ablation dynamics of the planar foil with preimposed sinusoidal ripples is investigated at the SG 100 kJ Laser Facility. A significant fraction of the second harmonics is observed and identified at the beginning of the ablative drive when the amplitude of the perturbation is within the linear regime. With radiation-hydrodynamic simulations and a developed simple model, we can reveal that such a novel phenomenon is due to the fact that a sustained deformation of the ablation front is initiated since the ablation pressure is directed to the normal direction of the perturbation surface. We find that this deformation dominates the early-time perturbation evolution and results in a specific stage in addition to the traditional ablative Richtmyer-Meshkov instability phase. Our results can be applicable to various regions such as implosions in inertial confinement fusion and the dynamics of molecular clouds in astrophysics.

This paper presents a numeric study of the dynamic stabilization of the ablative Rayleigh-Taylor instability (ARTI) in the presence of a temporally modulated laser pulse. The results show that the specially modulated laser produces a dynamically stabilized configuration near the ablation front. The physical features of the relevant laser-driven parameters in the unperturbed ablative flows have been analyzed to reveal the inherent stability mechanism underlying the dynamically stabilized configuration. A single-mode ARTI for the modulated laser pulse is first compared with that of the unmodulated laser pulse. The results show that the modulated laser stabilizes the surface perturbations and reduces the linear growth rate and enhancement of the cutoff wavelength. For multimode perturbations, the dynamic stabilization effect of the modulated laser pulse contributes to suppress the small-scale structure and reduce the width of the mixing layer. Moreover, the results show that the stabilization effect of the modulated laser pulse decreases as the maximum wavelength increases.