On the Aspects of a Convergent Shock Wave Impinging a Perturbed Density Interface

The detailed characterization of a fluid flow following a convergent shock wave impinging a perturbed density interface is an extremely complex task as this flow combines geometry effects, compressibility effects and turbulence. Nonetheless, more understanding is necessary to be able to develop models that help accurately predict the flow behavior when occurring in engineering applications. Such an application is Inertial Confinement Fusion (ICF), where turbulent mixing induced by the interaction of the shock wave with the fuel pellet is detrimental to the fusion process. This interaction triggers mixing due to baroclinic vorticity deposition at the density interface in a phenomenon known as the Richtmyer-Meshkov Instability (RM). Next, the Rayleigh-Taylor Instability (RT) is driving the final growth of the mixing layer limited by secondary instabilities such as the Kelvin-Helmholtz Instability (KH). These classical hydrodynamic instabilities (HI) trigger the mixing process that leads ultimately to a highly-mixed fluid layer. For this study, we simulate a cylindrical Sulfur hexafluoride (SF6) target immersed into an air medium. The incident shock wave is regarded as a Chisnell-type converging shock wave impinging into a perturbed cylindrical density discontinuity generated with a wave-like spatial perturbation spectra. Parameters of interest are the growth rate and width of the mixing layer at the density discontinuity. This study aims at describing and quantifying relevant aspects of these flows coupling mixing layer growth with perturbation modes.

Liquid temperature dependence of the shock formation in a cavitation bubble

The dependence of the radially convergent shock wave formation in a cavitation bubble on the surrounding liquid temperature TL in the range from 273.15 to 400 K is investigated at the liquid pressure equal to 50 bar. Realistic mathematical model is applied, in which the effects of the liquid compressibility, the heat conductivity of the vapor and liquid, the evaporation and condensation on the bubble surface are taken into account, wide-range equations of state are utilized. The governing equations of the vapor and liquid dynamics are solved numerically using a modification of the Godunov method of the second order of accuracy. It has been found that a radially convergent shock wave arises in the bubble in 273.15≤T_L≤375 К. In this interval, the distance between the shock wave formation position and the bubble surface decreases with decreasing the liquid temperature. The possibility of using a known simplified criterion of the formation of a shock wave inside a bubble to estimate its formation position under the studied conditions is considered. It is shown that with applying that criterion the shock wave formation position turns out to be correctly predicted at T_L≈325 К, while at T_L>325 К and T_L<325 К it is predicted closer to and more distant from the bubble surface, respectively.

Amplification of a Laser Beam for the Fast Ignition of a Thermonuclear Target

It is proposed to simultaneously compress a thermonuclear target and amplify a laser beam by a single z-pinch discharge. The laser beam is imploded and amplified by a cylindrical convergent shock wave inside a capillary, transforming it into a soft X-ray pulse for the fast ignition of the thermonuclear target. The target is compressed inside a liner by the z-pinch current. The capillary is attached to one end of the cylindrical target, and is protected by a radial wire spoke array fast opening switch against its premature implosion by the convergent shock wave. The z-pinch can be stabilized by placing it into a powerful vortex.