Rayleigh-Taylor instability amplification due to radiative losses

Summary form only given. Radiative losses are known to play an important role in the development of hydrodynamic instabilities in many astrophysical (Core-collapse supernovae; HH objects) and laboratory (Inertial confinement fusion) environments. The fielding of triple-annular gas-puff valves on university level pulsed-power generators [1][2] enables study of these instabilities in carefully controlled environments, for inviscid Re >> 1, non-diffusive Pe >> 1 fluids, where radiative losses on dynamically-relevant timescales can be significant. Furthermore, the acceleration of the unstable boundary and radiative cooling rates can both be specified, by variation of nozzle backing-pressures and gas species respectively.A 7 cm outer-diameter, triple-annular nozzle is used to inject gas into the 2.4cm anode-cathode gap of the (1 MA, 200 ns) COBRA generator. An annular current-carrying plasma, formed near the nozzle outer radius, is driven towards the axis of symmetry by the azimuthal magnetic field produced by the machine current. This low-density current-sheath sweeps up injected neutral gas ahead of it into a high-density shell, and the boundary between these layers is unstable to the Rayleigh-Taylor (RT) instability. RT growth is investigated in Argon (Ar) and Krypton (Kr) gas-puffs, initialized with radial mass-density profiles that are determined quantitatively by Planar Laser-Induced Fluorescence. Perturbation wavelengths and amplitudes are imaged at 10ns intervals using two four-frame XUV (10eV <; hν <; 1keV) cameras. Simultaneously, the temperature and velocity of the imploding shell is probed using a (527 nm, 4 GW) Thomson scattering diagnostic. Dominant wavelengths are observed at 1.5mm and 1.7mm for Ar and Kr shells respectively. Amplitude e-folding times of 20ns are recorded in Kr, 20% faster than in Ar under otherwise identical conditions. Ion temperatures of 100eV are recorded in Kr shells, ~40% lower than in Ar, and it appe- rs this cooling is responsible for the observed increase in RT growth rate.