Reduction of increment of Rayleigh-Taylor instability in specially designed multilayer inertial-confinement-fusion targets

摘要

The problem of hydrodynamic stability and mixing is very important for inertial-confinament-fusion (ICF) systems based upon high compression of fuel before ignition. The ablative drive of foils and compression of shells are unstable. The fundamental isobaric f(-) mode is the most destructive one. It conserves pressures in the Lagrangian particles. A way to remove this dangerous mode is presented, based on special distributions of mass among subshells in the multishell target. The obtained solution follows from a consideration of new, inverse-density polytropes that have negative values of the polytropic index N, rho(r)proportional to(r-r(V))(N), where r(V) is the radius of an inner, low-pressure. cavity filled with a fuel. Polytropes describe inhomogeneous incompressible and compressible cases. Density of material rho does not vanish in these distributions, as in the case of usual polytropes with N > 0 considered previously in geophysics and astrophysics. Conversely rho rises when we approach the boundary with vacuum. This property allows us to simulate multilayer distributions of rho that are typical for ICF targets. In these targets the high-density subshells surround the low pressure or vacuum cavity, while the outer subshells are made from low-density materials such as plastics, foams, and/or from composite materials. The proposed distributions are self-similar. Therefore their linear dynamics is scale invariant. New acoustic fundamental modes f(P)(+/-) are found and an interesting correspondence between acoustic and gravity modes is presented. (The f(-/+) or f(G)(+/-) fundamental modes are the well-known gravity modes.). [References: 25]