Direct-drive-implosion core conditions have been characterized on the 60-beam OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system with time-resolved Ar K-shell spectroscopy. Plastic shells with an Ar-doped deuterium fill gas were driven with a 23 kJ, 1 ns square laser pulse smoothed with 1 THz smoothing by spectral dispersion (SSD) and polarization smoothing (PS) using birefringent wedges. The targets are predicted to have a convergence ratio of ∼15. The emissivity-averaged core electron temperature (Te) and density (ne) were inferred from the measured time-dependent Ar K-shell spectral line shapes. As the imploding shell decelerates the observed Te and ne increase to 2.0 (±0.2) keV and 2.5 (±0.5)×1024 cm−3 at peak neutron production, which is assumed to occur at the time of the peak emissivity-averaged Te. At peak compression the ne increases to 3.1 (±0.6)×1024 cm−3 and the Te decreases to 1.7 (±0.17) keV. The observed core conditions are close to those predicted by a one-dimensional hydrodynamics code.

The chamber wall armor is subject to demanding conditions in inertial fusion energy (IFE)

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The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be 3.4(+/-1.2) g/cm(3) from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, 3.6(+/-1) g/cm(3), accounts for only approximately 50% of the neutron-burn-averaged electron density, n(e)=2.2(+/-0.4)x10(24) cm(-3).