Direct observation of density gradients in ICF capsule implosions via streaked Refraction Enhanced Radiography (RER)

We have performed refraction enhanced radiography (RER) measurements of indirect drive layered high density carbon capsule implosions relevant for inertial confinement fusion. Streaked RER data using a 5 µm wide imaging slit, backlit by a 7.8 keV Ni He-α laser driven x-ray source, shows features due to inflight density gradients in the ablator and fuel ice that are not visible in absorption only radiographs. To avoid motional blurring at smaller in-flight radii, we concentrate our probe to the main compression and N+1 shock phases. During the main compression phase, both simulations and data show fringes consistent with steep density gradients. During the later N+1 shock phase we see loss of fringes and hence infer less fuel compression than simulated, that may be caused by ice-ablator mix. Quantitative analysis shows that at the ablation front during the main compression phase, the simulated density differential agrees with the data, but the inferred scale length is 50% longer than simulated. During the N+1 shock phase, the data shows 2x higher ablation front density than simulated for similar scale lengths that may be affected by data cross talk with the reduced fuel compression at the ice-ablator interface.