Density gradient effects in weakly nonlinear ablative Rayleigh-Taylor instability

Journal Article · Sun Jan 15 04:00:00 EST 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3677821· OSTI ID:22043591

Wang, L F; Ye, W H; He, X T ^[1]

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1. HEDPS and CAPT, Peking University, Beijing 100871 (China)

In this research, density gradient effects (i.e., finite thickness of ablation front effects) in ablative Rayleigh-Taylor instability (ARTI), in the presence of preheating within the weakly nonlinear regime, are investigated numerically. We analyze the weak, medium, and strong ablation surfaces which have different isodensity contours, respectively, to study the influences of finite thickness of ablation front on the weakly nonlinear behaviors of ARTI. Linear growth rates, generation coefficients of the second and the third harmonics, and coefficients of the third-order feedback to the fundamental mode are obtained. It is found that the linear growth rate which has a remarkable maximum, is reduced, especially when the perturbation wavelength {lambda} is short and a cut-off perturbation wavelength {lambda}{sub c} appears when the perturbation wavelength {lambda} is sufficiently short, where no higher harmonics exists when {lambda}<{lambda}{sub c}. The phenomenon of third-order positive feedback to the fundamental mode near the {lambda}{sub c}[J. Sanz et al., Phys. Rev. Lett. 89, 195002 (2002); J. Garnier et al., Phys. Rev. Lett. 90, 185003 (2003); J. Garnier and L. Masse, Phys. Plasmas 12, 062707 (2005)] is confirmed in numerical simulations, and the physical mechanism of the third-order positive feedback is qualitatively discussed. Moreover, it is found that generations and growths of the second and the third harmonics are stabilized (suppressed and reduced) by the ablation effect. Meanwhile, the third-order negative feedback to the fundamental mode is also reduced by the ablation effect, and hence, the linear saturation amplitude (typically {approx}0.2{lambda} in our simulations) is increased significantly and therefore exceeds the classical prediction 0.1{lambda}, especially for the strong ablation surface with a small perturbation wavelength. Overall, the ablation effect stabilizes the ARTI in the weakly nonlinear regime. Numerical results obtained are in general agreement with the recent weakly nonlinear theories and simulations as proposed [J. Sanz et al., Phys. Rev. Lett. 89, 195002 (2002); J. Garnier et al., Phys. Rev. Lett. 90, 185003 (2003); J. Garnier and L. Masse, Phys. Plasmas 12, 062707 (2005)].

• OSTI ID: 22043591
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 1 Vol. 19; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABLATION
AMPLITUDES
COMPUTERIZED SIMULATION
DENSITY
DISTURBANCES
FEEDBACK
HARMONICS
HEAT TREATMENTS
NUMERICAL ANALYSIS
PERTURBATION THEORY
PLASMA DENSITY
PLASMA SIMULATION
RAYLEIGH-TAYLOR INSTABILITY
SATURATION
SURFACES
WAVELENGTHS