Inertial confinement fusion (ICF) experiments rely on the compression of a spherical capsule containing tritium and deuterium to achieve thermonuclear fusion. Rapid ablation of the capsule surface produces a reactive force that compresses the capsule. Carbon-based capsule materials currently used include low density, glow discharge polymer (GDP) and polycrystalline diamond. An ideal capsule material would have the high density of diamond with the amorphous nature of GDP to reduce asymmetries caused by a random crystalline structure during compression. An intermediate material—diamond-like carbon (DLC)—has an amorphous structure and density that falls between GDP and diamond. However, DLC with low stress and low impurity levels has been difficult to produce.
We investigated the feasibility of using a magnetically enhanced, hollow-cathode plasma source to produce thick (50–200 µm), low-stress, diamond-like carbon films for ICF ablator applications. The coatings produced during the course of this work have been shown to be amorphous, to have a higher density than traditional GDP ablators (1.6–1.7 g/cc), and to have low stress (67–113 MPa). The coatings can be deposited at the high thicknesses required for ICF capsule requirements. Using atomic force microscopy on a 45 micron-thick coating, we measured the films to have grain sizes on the order of 20 nanometers and a root-mean-squared surface roughness of 0.5 nanometers.
Our research leveraged and advanced Lawrence Livermore National Laboratory's core competency in advanced materials. The capabilities of the Laboratory's hollow cathode plasma source were also explored, extending its range of use beyond that of a low energy oxygen plasma source for etching diamond anvils. Our results support advancing capabilities in the ICF mission area.
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