Multishock compression of dense cryogenic hydrogen-helium mixtures up to 60 GPa: Validating the equation of state calculated from first principles

摘要: Multishock compression experiments on hydrogen-helium (${\mathrm{H}}_{2}$-He) mixtures have been performed via a two-stage light-gas gun for providing equations of state (EOS) covering wide pressure range. The initial gaseous ${\mathrm{H}}_{2}$-He sample was precompressed to 20--30 MPa and cooled down around 90 K gain high density. Up three shock compressions were clearly observed from the time-resolved light radiance shocked recorded by multichannel optical pyrometer. measured EOS data mixture reached an unexplored range up 60 GPa, which is well in molecular-to-atomic transition regime. wide-range experimental are used validate state-of-the-art first-principles simulation methods. It found that density functional theory molecular dynamics (DFT-MD) simulations underestimate dissociation hydrogen therefore predict be stiffer than A careful analysis pair correlation functions comparison with results pure revealed DFT-MD might overestimate effects helium bond molecule when mixed helium. Finally, current measurements linear-mixing ab initio [Astrophys. J. Suppl. S. 215, 21 (2014)] widely astrophysics.