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Proceedings Paper

Experimental study on ablative stabilization of Rayleigh-Taylor instability of laser-irradiated targets
Author(s): Keisuke Shigemori; Tatsuhiko Sakaiya; Kazuto Otani; Shinsuke Fujioka; Mitsuo Nakai; Hiroshi Azechi; Hiroyuki Shiraga; Yohei Tamari; Kazuki Okuno; Atsushi Sunahara; Hideo Nagatomo; Masakatsu Murakami; Katsunobu Nishihara; Yasukazu Izawa
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Paper Abstract

Hydrodynamic instabilities are key issues of the physics of inertial confinement fusion (ICF) targets. Among the instabilities, Rayleigh-Taylor (RT) instability is the most important because it gives the largest growth factor in the ICF targets. Perturbations on the laser irradiated surface grow exponentially, but the growth rate is reduced by ablation flow. The growth rate γ is written as Takabe-Betti formula: γ = [kg/(1+kL)]1/2–βkm/pa, where k is wave number of the perturbation, g is acceleration, L is density scale-length, β is a coefficient, m is mass ablation rate per unit surface, and ρa is density at the ablation front. We experimentally measured all the parameters in the formula for polystyrene (CH) targets. Experiments were done on the HIPER laser facility at Institute of Laser Engineering, Osaka University. We found that the β value in the formula is ~ 1.7, which is in good agreements with the theoretical prediction, whereas the β for certain perturbation wavelengths are larger than the prediction. This disagreement between the experiment and the theory is mainly due to the deformation of the cutoff surface, which is created by non-uniform ablation flow from the ablation surface. We also found that high-Z doped plastic targets have multiablation structure, which can reduce the RT growth rate. When a low-Z target with high-Z dopant is irradiated by laser, radiation due to the high-Z dopant creates secondary ablation front deep inside the target. Since, the secondary ablation front is ablated by x-rays, the mass ablation rate is larger than the laser-irradiated ablation surface, that is, further reduction of the RT growth is expected. We measured the RT growth rate of Br-doped polystyrene targets. The experimental results indicate that of the CHBr targets show significantly small growth rate, which is very good news for the design of the ICF targets.

Paper Details

Date Published: 20 September 2004
PDF: 8 pages
Proc. SPIE 5448, High-Power Laser Ablation V, (20 September 2004); doi: 10.1117/12.548818
Show Author Affiliations
Keisuke Shigemori, Osaka Univ. (Japan)
Tatsuhiko Sakaiya, Osaka Univ. (Japan)
Kazuto Otani, Osaka Univ. (Japan)
Shinsuke Fujioka, Osaka Univ. (Japan)
Mitsuo Nakai, Osaka Univ. (Japan)
Hiroshi Azechi, Osaka Univ. (Japan)
Hiroyuki Shiraga, Osaka Univ. (Japan)
Yohei Tamari, Osaka Univ. (Japan)
Kazuki Okuno, Osaka Univ. (Japan)
Atsushi Sunahara, Osaka Univ. (Japan)
Hideo Nagatomo, Osaka Univ. (Japan)
Masakatsu Murakami, Osaka Univ. (Japan)
Katsunobu Nishihara, Osaka Univ. (Japan)
Yasukazu Izawa, Osaka Univ. (Japan)

Published in SPIE Proceedings Vol. 5448:
High-Power Laser Ablation V
Claude R. Phipps, Editor(s)

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