Observation of perturbations in underdense plasmas induced by ablative Rayleigh–Taylor instability

Plasma homogeneity is of great importance for inertial confinement fusion because of its effects on laser absorption and subsequent implosion. Perturbations occurring near the ablation front and induced by hydrodynamic instabilities may influence the homogeneity of the underdense corona as the plasma expands. In this paper, perturbations in underdense plasmas produced from plastic targets at laser irradiances of ∼ 10 15 W/cm2 are observed, which were effectively suppressed by the application of a continuous phase plate. Taking account of the directions of the perturbations, the laser, and the target, the perturbations may be interpreted as the result of ablative Rayleigh–Taylor instability. Calculations of their linear growth rates are performed based either on radiation hydrodynamics simulations or on a fixed cutoff wavenumber corresponding to the measured spectra of the perturbations, and better agreement with the experimental results is found for the second approach. The difference between the two approaches is interpreted in terms of different ranges of the Froude number, which in the experiments was greater than unity, beyond the usual range at relatively low laser irradiance.