Fig. 2: Time-resolved x-ray spectroscopy experiment of warm-/hot-dense plasmas at white-dwarf’s envelope conditions of Gbar pressures.

a Schematic targets for implosion spectroscopy on OMEGA. b Example of streaked spectra measured in experiments. c The pressure-density region probed by various HED experiments: GEKKO⁴⁷, OMEGA⁴⁸, Nova⁴⁵, NIF by Doeppner et al.¹¹, NIF by Kritcher et al.^51,52, NIF by Fletcher et al.⁴⁹, as well as non-Hugoniot work by Doeppner et al.⁵⁰ on NIF. d The density-temperature conditions of a typical white dwarf of 0.6M_ʘ (0.6 solar mass) as it’s cooling down from hot and young state (right) to older and colder structures (left). Convective regions in the stars are shown in red. The regime probed by the experiments is shown by the green dashed circle. Inferred from DRACO simulations, the plasma temperature and density conditions of the imploding Cu-doped layer vary from kT ≈ 10‒50 eV and ρ ≈ 2‒10 g cm⁻³ (in-flight stage) to kT ≈ 200‒500 eV and ρ ≈ 10‒25 g cm⁻³ during the stagnation.