Re-emission technique for early time, hohlraum radiation symmetry measurements on SGⅡ facility

Indirectly driven capsule implosions are driven by four shock waves whose strength and relative timing must be controlled to high precision to keep the fuel on a low adiabat. The symmetry during the first 2 ns should be tuned carefully. The mainline tuning targets chosen are the high Z re-emission spheres. For record of instantaneous asymmetry during the first 2 ns, multiple images in the time of the soft X-ray re-emission from a non-imploding Bi ball on SGⅡ facility were taken in 2011. The re-emitted images with hohlraum lengths of 1350 m and 1500 m were obtained and the experimental P2/P0 and P4/P0 time histories were deduced. A simple analytical view-factor model is established, and the simulation result of P2/P0 is in agreement with the measured P2/P0.