Creating and probing dense plasmas relevant to stellar interiors and inertial fusion energy

I will report on recent experiments at the National Ignition Facility (NIF) and the European XFEL to mimic extreme conditions comparable to the interior of small stars or the envelope of white dwarfs. Within the Discovery Science program of NIF, we were able to implode cryogenic hydrogen capsules to densities around 100 g/cm³ and temperatures around 200 eV. With X-ray probing, we could measure the free-free absorption of hydrogen at conditions relevant to the interior of red dwarfs (also called M dwarfs), which represent the most abundant type of stars in our galaxy. In addition, using a slow implosion and a hydrogen ice layer that is thicker than the ablator, the applied drive scheme is very similar to compression scenarios required for typical fast or shock ignition approaches proposed for inertial fusion energy. The implementation of our platform design could identify several challenges in this direction. At the European XFEL, we were able drive thin carbon and hydrocarbon samples with laser intensities of ~10¹⁶ W/cm² at ~1 ps pulse duration and heat these samples isochorically to temperatures of 50-100 eV. The samples were probed via X-ray Thomson scattering to determine the temperature and the ionization of the carbon ions. In this way, we can benchmark the EOS of carbon and C-H mixtures at conditions relevant to the envelopes of white dwarfs. At the same, time valuable information on the picosecond material response to drive intensities relevant to the shock ignition approach for inertial fusion energy is obtained.