Absorption Spectroscopy in Photoionization Front Laboratory Experiments *

 

Photoionization fronts are meaningful drivers of transformation for the evolution of the early universe and this remain difficult to reproduce in laboratory experiments. The first stars heated and ionized the surrounding gas creating photoionization fronts giving structure to galaxies. We aim to recreate similar conditions in the laboratory. Within these experiments, UV photons irradiate a gold foil to generate an x-ray photon source of ~90 eV that is incident on nitrogen/argon gas. A spherical nickel-lined CH capsule creates a continuum x-ray backlighter source of about 2-4 keV and line emission 7.4 keV due to Ni dopant. Using the absorption spectroscopy technique, we will infer the temperature, density and ionization state of the heated argon gas, which has absorption features within the 2.7-3.2 keV range. We use these plasma parameters to calculate key dimensionless numbers for photoionization. We present the preliminary results of HED experiments at the OMEGA Laser Facility.