Figure from the DOE Report May, 2018

May 2018 DOE Report

Backlighter-Intensity Improvements for Radiography of Cryogenic Implosions

X-ray radiography of direct-drive cryogenic DT implosions on OMEGA is challenging because of the low opacity of the DT shell and the very bright self-emission of the hot core. A narrowband (+5-eV), time-gated (~40-ps) crystal imaging system with a Si Heα backlighter ( = 1.865 keV), driven by 1.5-kJ, 20-ps pulses from OMEGA EP was set up to radiograph these implosions. First radiographs of cryogenic implosions were recorded with this configuration +50 to 100 ps before peak compression, but at peak compression the signal from the self-emission of the hot core was still significantly stronger than the backlighter. A program was started with experiments on OMEGA EP to evaluate options that could improve the backlighter brightness. In the first experiments, three different setups were tested: (1) the effects of a laser prepulse with solid, flat targets; (2) SiO2 foams of different density; and (3) the use of a thin CH shield to confine the laser-heated Si plasma.

Shown here: time-integrated Si K-shell spectra showing the improvement in x‑ray fluence from a Si target with a CH shield (blue) compared to a flat Si target (red).

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