Fig. S4.

Radiative cooling of the plasma. (A) Calculation of the Planck mean emission opacity (${\kappa }_P$) for argon as a function of typical values of density and temperature expected in the experiment. (B) 1D radiation hydrodynamic simulation with the code HELIOS showing the rapid cooling of an argon plasma sphere initialized with radius of 0.5 cm, $T_e=3$ eV, mass density of $9\times {10}^{-6}$ g/cm³, and outward radial velocity of 14 km/s. Results from a calculation performed with multigroup radiation diffusion turned on are shown with solid lines. Results from a similar calculation but without radiation diffusion are shown with dashed lines.