Neutron Yield Study of Direct-Drive, Low-Adiabat Cryogenic D2 Implosions on OMEGA Laser System
Neutron yields of direct-drive, low-adiabat (alpha ~~ 2 to 3) cryogenic D2 target implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have been systematically investigated using the two-dimensional (2D) radiation hydrodynamics code DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)]. Low-mode (ell <- 12) perturbations, including initial target offset, ice-layer roughness, and laser-beam power imbalance, were found to be the primary source of yield reduction for thin-shell (5 um), low-alpha, cryogenic targets. The 2D simulations of thin-shell implosions track experimental measurements for different target conditions and peak laser intensities ranging from 2.5 x 10^14–6 x 10^14 W/cm^2. Simulations indicate that the fusion yield is sensitive to the relative phases between the target offset and the ice-layer perturbations. The results provide a reasonable good guide to understanding the yield degradation in direct-drive, low-adiabat, cryogenic, thin-shell-target implosions. Thick-shell (10 um) implosions generally give lower yield over clean than low-ell-mode DRACO simulation predictions. Simulations including the effect of laser-beam nonuniformities indicate that high-ell-mode perturbations caused by laser imprinting further degrade the neutron yield of thick-shell implosions. To study ICF compression physics, these results suggest a target specification with a <-30 um offset and ice-roughness of sigma_rms < 3 um are required.
- Research Organization:
- Univ. of Rochester, NY (United States). Lab. for Laser Energetics
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC52-08NA28302
- OSTI ID:
- 967365
- Report Number(s):
- DOE/NA/28302-913; 2008-131; 1896
- Journal Information:
- Physics of Plasmas, Vol. 16, Issue 11
- Country of Publication:
- United States
- Language:
- English
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