Direct-drive implosion experiment of diamond capsules fabricated with hot filament chemical vapor deposition technique

Abstract

Diamond is a promising alternative capsule material for direct-drive inertial confinement fusion. Previous investigations suggest that the stiffness and higher density of diamond can mitigate laser imprinting, which is an initial perturbation on the ablation surface caused by non-uniform laser irradiation. We conduct diamond capsule fabrication using the hot filament chemical vapor deposition (HF-CVD) technique. This technique is the most suitable diamond deposition method in terms of mass production, since the deposition area can be easily extended just by increasing the number of hot filaments. This paper presents the first direct-drive implosion experiment concerning diamond capsules fabricated using the HF-CVD technique. The compression of thin diamond capsules, with an inner capsule diameter of 482 μm and a shell thickness of 1.6 μm, is successfully achieved, and the implosion trajectory of diamond capsules, with the same diameter and thickness, is consistent with 1D radiation hydrodynamic simulation calculations. However, for diamond capsules with an inner diameter of 482 μm and a shell thickness of 2.4 μm, asymmetry of the implosion trajectory and unexpected x-ray emission are observed. This is attributed to the remaining silicon (Si) mold inside the capsule left over from the fabrication process, revealing that the etching method of Si in diamond capsules should be improved.