A number of applications utilise the energy focussing potential of imploding shells to dynamically compress matter or magnetic fields, including magnetised target fusion schemes in which a plasma is compressed by the collapse of a liquid metal surface. This paper examines the effect of fluid rotation on the Rayleigh-Taylor (RT) driven growth of perturbations at the inner surface of an imploding cylindrical liquid shell which compresses a gas-filled cavity. The shell was formed by rotating water such that it was in solid body rotation prior to the piston-driven implosion, which was propelled by a modest external gas pressure. The fast rise in pressure in the gas-filled cavity at the point of maximum convergence results in an RT unstable configuration where the cavity surface accelerates in the direction of the density gradient at the gas-liquid interface. The experimental arrangement allowed for visualization of the cavity surface during the implosion using high-speed videography, while offering the possibility to provide geometrically similar implosions over a wide range of initial angular velocities such that the effect of rotation on the interface stability could be quantified. A model developed for the growth of perturbations on the inner surface of a rotating shell indicated that the RT instability may be suppressed by rotating the liquid shell at a sufficient angular velocity so that the net surface acceleration remains opposite to the interface density gradient throughout the implosion. Rotational stabilisation of highmode-number perturbation growth was examined by collapsing nominally smooth cavities and demonstrating the suppression of small spray-like perturbations that otherwise appear on RT unstable cavity surfaces. Experiments observing the evolution of lowmode-number perturbations, prescribed using a mode-6 obstacle plate, showed that the RT-driven growth was suppressed by rotation, while geometric growth remained present along with significant non-linear distortion of the perturbations near final convergence. †

Abstract. The spall strength of polydimethylsiloxane silicone oils has been studied using the planar impact of thin flyers to generate large transient negative pressures near the free surface of target samples. The liquids were contained within sealed capsules in which a 4-µm-thick aluminized Mylar diaphragm formed a free surface at the back of the sample. The liquid targets were impacted by PMMA flyers at velocities ranging from 130 to 700 m/s using a 64-mm-bore gas-gun, thus allowing for large variations in the strain rate and incident shock pressure. The peak tension in the liquid was determined by monitoring the free surface velocity using a photonic Doppler velocimetry (PDV) system. The paper focuses on the study of a system of silicone oils having vastly different viscosities (5 cSt to 1000 cSt), but otherwise similar liquid properties. The effect of viscosity on spall strength is compared to previously published data and models.

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Laboratory experiments of hypervelocity impacts on aluminum, nylon and high-explosive targets are presented. Spectral measurements of the impact flash are recorded, together with radiometric measurements to derive the temperature of the flash. Such experiments aim at demonstrating that the impact flash produced by a ballistic missile interception contains the spectral information required to identify the content of the intercepted missile. It is shown that the elements that are part of the aluminum projectile and/or aluminum target are successfully identified from the obtained spectra. For the case of a nylon/aluminum target organic molecular emission lines characteristic of CN and C 2 are also identified. The CN molecular band is also observed for the case of a high-explosive target, although the detection of organic elements from such targets is more difficult than for nylon targets. In most cases, the temperature of the impact flash measured using the radiometer is in the range 2500 -4000 K, whereas a comparison between simulated and experimental spectra shows temperatures up to 9000 K. Hence a conclusive impact flash temperature could not be obtained.

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