Abstract
In inertial confinement fusion (ICF), polycrystalline diamond—referred to as high density carbon (HDC)—has become a promising ablator candidate. However, with smaller grain size and lower initial density, the equation of state (EOS) for HDC can deviate from that for single-crystal diamond, which could be a concern for ICF designs, but current experimental EOS studies for HDC are far from sufficient to clarify how initial density affects target compressibility. Presented here are measurements of the Hugoniot for HDC with an initial density of 3.23 g/cm3 at pressures of 17–26 Mbar. Combined with experimental data reported for nanocrystalline diamond (NCD), a stiffer compressibility of NCD due to lower initial density is confirmed. Two porous models are used for comparison and seem to offer better agreement compared with SESAME databases. Also, the effect of temperature on the Grüneisen parameter, which is usually neglected, might need to be considered for NCD under these conditions. The present data offer important support for EOS studies relevant to ICF and constrain the construction of wide-range EOS.
Highlights
Its unique properties and extensive applications make diamond an important research object in many fields, including material science, condensed matter physics, energy science and technology, and planetary science
With smaller grain size and lower initial density, the equation of state (EOS) for high density carbon (HDC) can deviate from that for single-crystal diamond, which could be a concern for inertial confinement fusion (ICF) designs, but current experimental EOS studies for HDC are far from sufficient to clarify how initial density affects target compressibility
HDC is usually made by chemical vapor deposition (CVD) with micrometer or nanometer grain size and lower initial density than that of single-crystal diamond (SCD),21–23 and Hugoniot variations due to these factors could be an important concern for ICF designs
Summary
Its unique properties and extensive applications make diamond an important research object in many fields, including material science, condensed matter physics, energy science and technology, and planetary science. The HDC used in ICF is not SCD but polycrystalline diamond with lower initial density and smaller grain size, but there are insufficient experimental data on HDC to provide either numerical design benchmarks or an understanding of how the initial density affects target compressibility.. Gregor et al. compared the Hugoniot data for both SCD with an initial density of 3.515 g/cm and nanocrystalline diamond (NCD) with an initial density of ∼3.36 g/cm at pressures of up to 2.6 TPa; the NCD data were stiffer than the SCD data and might be well interpreted by a porous model. For better understanding of the initial density effects for ICF designs, Hugoniot experiments on nano-sized polycrystalline diamond with a lower initial density of ∼3.23 g/cm were conducted at a 10-kJ laser facility..
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