We present scaled demonstrations of backlighter sources, emitting bremsstrahlung x rays with photon energies above 75 keV, that we will use to record x-ray Compton radiographic snapshots of cold dense DT fuel in inertial confinement fusion implosions at the National Ignition Facility (NIF). In experiments performed at the Titan laser facility at Lawrence Livermore National Laboratory, we measured the source size and the bremsstrahlung spectrum as a function of laser intensity and pulse length from solid targets irradiated at 2x10(17)-5x10(18) W/cm(2) using 2-40 ps pulses. Using Au planar foils we achieved source sizes down to 5.5 microm and conversion efficiencies of about 1x10(-13) J/J into x-ray photons with energies in the 75-100 keV spectral range. We can now use these results to design NIF backlighter targets and shielding and to predict Compton radiography performance as a function of the NIF implosion yield and associated background.

The Jϭ0→2 Raman signal from solid Jϭ0 D 2 or H 2 reveals the hcp structure when deposited at a rate 0.1рR͑m/min͒р40 onto MgF 2 at T d /T tp Ͼ0.3, a mixture of hcp and fcc crystals at 0.2ϽT d /T tp Ͻ0.3 and possibly a randomly stacked close-packed structure at T d /T tp Ͻ0.2, where T tp is the triple point temperature. Non-hcp crystals transform to hcp continuously and irreversibly with increasing T. Finally, the crystal size decreases with decreasing T d and increasing R, from ϳ1 mm at T d ϳ0.8T tp and Rϳ2 m/min to ϳ1 m at 0.25 T tp and Rϳ40 m/min.

The dependence of stimulated backward and forward scattered light on ion acoustic damping (νi) is measured for the first time in a long scale length He/H2 composition plasma at a density of 0.08 critical for 351-nm laser light. Both the stimulated Raman and Brillouin backscattering decrease with increasing ion acoustic damping. Modeling of the backward scattering agrees with the measurements when the Langmuir and ion acoustic fluctuations saturate at δn/n=0.01 and 0.001, respectively. These low saturation levels cannot be explained using standard nonlinear wave decay saturation mechanisms and may indicate that other saturation mechanisms are active in this plasma. Modeling of the forward scattering agrees qualitatively with the measurements and provides an estimate of the density fluctuations in the plasma.

We present an instrument platform for studying shock-compressed deuterium on moderately sized laser facilities. The target is designed for cryogenic liquid deuterium to be compressed with a sub-kJ laser pulse. The x-ray probe is the narrow band 2005 eV Si Ly-α resonance produced by a 200 J laser incident on a Si 3 N 4 foil. Scattered x-ray collection occurs in the backward and forward directions; spectral dispersion with Bragg crystals yields the plasma conditions of density and temperature. Additionally, the shock is probed with velocity interferometry. Combined with the electron density measurements from forward scattering, this allows average ionization state to be inferred. Proof of principle experiments demonstrate the viability of this technique for studies of the ionization of deuterium along the Hugoniot.

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