High-density carbon (HDC) has emerged as a crucial ablator material for achieving ignition in inertial confinement fusion (ICF), owing to its high atomic density and efficient energy coupling. In practical ICF capsules, however, HDC typically exists as polycrystalline or nanocrystalline diamond, whose grain structure may introduce small-scale inhomogeneities. Diamond-like carbon (DLC), a dense carbon material without long-range crystalline order, thus presents a promising alternative to HDC. Nevertheless, it remains unclear whether the structural differences between DLC and nanocrystalline HDC significantly affect their compression responses under ICF-relevant extreme conditions.
    Here, we conducted high-precision principal Hugoniot measurements on HDC and DLC samples with similar initial densities but distinctly different microstructures using the ShenGuang-III prototype laser facility. The HDC sample used was nanocrystalline diamond, whereas the DLC sample was predominantly amorphous and contained only a small fraction of diamond nanocrystals (with sizes of ~5–6 nm). The experiments covered a pressure range of approximately 8–22 Mbar, with a density uncertainty of less than 4%. In the absolute density-pressure space, the DLC data at 3.23 g·cm⁻³ appeared stiffer than the HDC data at 3.31 g·cm⁻³. However, comparisons with previously density-matched HDC data, demonstrated that this apparent offset primarily stems from the difference in initial density rather than the structural discrepancy between DLC and HDC. In the normalized ρ/ρ0-P space, the DLC data overlapped with those HDC within the experimental uncertainty. These results indicate that the Hugoniot response of carbon in the multi-megabar regime is mainly governed by the initial density and is not highly sensitive to the ambient microstructure. This work provides fundamental insights into the behavior of carbon under extreme conditions relevant to inertial confinement fusion and high-energy-density physics.
 

carbon,shock,Hugoniot,multi-megabar