Experimental techniques for measuring Rayleigh–Taylor instability in inertial confinement fusion

Abstract

Rayleigh–Taylor (RT) instability is one of the major concerns in inertial confinement fusion (ICF) because it amplifies target modulations in both acceleration and deceleration phases of implosion, which leads to shell disruption and performance degradation of imploding targets. This article reviews experimental results of the RT growth experiments performed on OMEGA laser system, where targets were driven directly with laser light. RT instability was studied in the linear and nonlinear regimes. The experiments were performed in acceleration phase, using planar and spherical targets, and in deceleration phase of spherical implosions, using spherical shells. Initial target modulations consisted of two-dimensional (2D) pre-imposed modulations, and 2D and three-dimensional (3D) modulations imprinted on targets by the nonuniformities in laser drive. In planar geometry, the nonlinear regime was studied using 3D modulations with broadband spectra near nonlinear saturation levels. In acceleration-phase, the measured modulation Fourier spectra and nonlinear growth velocities are in good agreement with those predicted by Haan's model (Haan 1989 Phys. Rev. A 39 5812). In a real-space analysis, the bubble merger was quantified by a self-similar evolution of bubble size distributions (Oron et al 2001 Phys. Plasmas8 2883). The 3D, inner-surface modulations were measured to grow throughout the deceleration phase of spherical implosions. RT growth rates are very sensitive to the drive conditions, therefore they can be used to test and validate drive physics in hydrodynamic codes used to design ICF implosions. Measured growth rates of pre-imposed 2D target modulations below nonlinear saturation levels were used to validate nonlocal thermal electron transport model in laser-driven experiments.