Experimental observations of turbulent mixing due to Kelvin–Helmholtz instability on the OMEGA Laser Facility

• Published in: Physics of plasmas 2012-09, Vol.19 (9)
• Main Authors: Smalyuk, V A, Hansen, J F, Hurricane, O A, Langstaff, G, Martinez, D, Park, S, Raman, K, Remington, B A, Robey, H F, Schilling, O
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION; ENGINEERING; Foils; Instability; Lasers; Perturbation methods; Plasmas; Plastic foam; Stability
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4752015

Shear-flow, Kelvin-Helmholtz (KH) turbulent mixing experiments were performed on the OMEGA Laser Facility [Boehly , Opt. Commun. 133, 495 (1997)] in which laser-driven shock waves propagated through a low-density plastic foam placed on top of a higher-density plastic foil. The plastic foil was comprised a thin iodine-doped plastic tracer layer bonded on each side to an undoped density-matched polyamide-imide plastic. Behind the shock front, lower-density foam plasma flowed over the higher-density plastic plasma, such that the interface between the foam and plastic was KH unstable. The initial perturbations consisted of pre-imposed, sinusoidal 2D perturbations, and broadband 3D perturbations due to surface roughness at the interface between the plastic and foam. KH instability growth was measured using side-on radiography with a point-projection 5-keV vanadium backlighter. Time-integrated images were captured on D-8 x-ray film. Spatial density profiles of iodine-doped plastic mixed with foam were inferred using x-ray radiographs. The mixing layer ensuing from the KH instability with layer width up to similar to 100 mu m was observed at a location similar to 1 mm behind the shock front. The measured mixing layer width was in good agreement with predictions based on a simple self-similar model of KH instability growth using an estimate of the shear velocity obtained from numerical simulations of the experiments.