Rayleigh–Taylor instabilities (RTI) play a central role in a wide range of high-energy-density systems, from inertial confinement fusion capsules—where their growth can impede ignition—to large-scale astrophysical structures such as supernova remnants. In these systems, the nonlinear development of RTI leads to symmetry breaking, interfacial mixing, and, in some cases, the onset of turbulence. Accurately characterizing their growth and understanding the physical mechanisms governing their evolution are therefore essential for predictive modeling.

However, direct observation of RTI in such environments remains challenging due to limitations in diagnostic capabilities, as well as constraints imposed by geometry, scale, and distance. In this context, dedicated laboratory laser experiments offer a unique opportunity to probe instability dynamics under controlled and reproducible conditions, and to access regimes relevant to both laboratory and astrophysical plasmas [1,2].

In this talk, we present results from a recent experiment conducted at the XFEL facility SACLA, employing sub-micron-resolution diagnostics to directly resolve the evolution of RTI structures [3]. The experiment investigates the growth of RTI in media with varying density contrasts, which simultaneously affect the deceleration and the Atwood number—two key parameters governing instability dynamics. Particular attention is given to the nonlinear phase of the instability, including the transition toward a mixing regime. By characterizing this mixing phase, we provide new insights into the pathways leading from coherent instability growth to more complex, potentially turbulent flows.
[1] C.C. Kuranz et al., Nat. Comm. 9, 1564 (2018)
[2] G. Rigon et al., Phys Rev E. 100, 021201 (2019)
[3] G. Rigon et al., Nat. Comm. 12, 2679 (2021)

hydrodynamic instability,laser plasma,High Energy Density Physics