Opacity Measurements on Fully Characterized 1.3 MK Titanium Plasmas

X-ray transmission spectra from fully characterized, high temperature plasmas provide validation benchmarks for high-energy-density physics models of interest to stellar astrophysics. This work presents new data from experiments at the Omega laser. 24 beams (at $\approx$ 500J/beam) heat the outer chambers of a 3-part (shine-shielded), 1.6 mm diameter hohlraum. The outer chambers radiatively heat a CH-tamped Ti foil in the center. Other beams drive 2 backlighters: a rear wall burnthrough halfraum, and a Kr-filled CH capsule implosion. Looking through the sample to these backlighters, 2 spectrometers measure the sample transmission from 250-1600 eV and 3000-5500 eV, respectively. The lower energy band encompasses the Rosseland mean opacity, governing radiation flow in stellar interiors. Plasma density of 0.05 g/cc, measured by expansion radiography, agrees with pre-shot calculations. Plasma temperature of 110-125 eV (1.3 MK), inferred from n=1 to n=2 titanium absorption lines, is 10-30\% below predictions. Use of similar techniques on the National Ignition Facility could validate stellar models in stellar core conditions.