Progress on key physical issues of double-shell volume ignition targets

Background Double-shell volume ignition is a highly promising ignition approach in the field of inertial confinement fusion, capable of achieving fusion ignition at a low temperature of～2.5 keV and a convergence ratio of approximately 10.

Purpose This study aims to conduct in-depth analysis of the critical physical issues of double-shell targets, including volume ignition conditions, the evolution of radiation drive asymmetry, and the feedthrough effects of multi-interface hydrodynamic instabilities.

Methods Based on a zero-dimensional energy balance model, a critical ignition criterion for double-shell target volume ignition is established. An analytical theoretical model is proposed for the development and transfer of drive asymmetry in double-shell targets. The linear or non-linear growth models of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instability, and multi-scale numerical simulations are used to investigate the feed-in mechanism of the key interface perturbations in double-shell targets.

Results the modulation mechanisms of the inner-outer shell mass ratio and kinetic energy coupling coefficient on the drive asymmetry feedthrough process are revealed, and an effective method for modulating the implosion compression symmetry in the fuel region is proposed. Under the optimal symmetry condition on a hundred-kilojoule laser facility, the P2 asymmetry of the core morphology is reduced to −2.1%. Furthermore, this work reveals that the outer interface of the inner shell is the dominant hydrodynamic instability interface limiting the implosion performance of double-shell targets, elucidates the perturbation feedthrough mechanism of the thin inner shell, and proposes a theoretical design to suppress instability growth at the dominant interface through a cushion layer. The CH cushion layer can reduce the perturbation growth factor at the outer interface of the inner shell by 30% and decrease the feedthrough perturbation amplitude at the fuel interface by 60%.ConculsionsThese theoretical and experimental results provide valuable references for addressing the critical technical challenges of double-shell volume ignition.