Fast-formed liquid surfaces for inertial confinement fusion targetshells

摘要

Advanced ICF targets will have an inner layer of solid or liquidfuel. Their inner surfaces must be smooth and contamination free. All ofthe current means to produce such a surface have problems: Liquidsurfaces sag, solid surfaces tend to facet, and polymer-foam-stabilizedsurfaces are contaminated by carbon from the foam. An alternative may beto generate a liquid surface immediately before a shot by rapid thermalexpansion of a fuel-saturated foam-walled capsule. This approach makesuse of the large coefficient of expansion of liquid hydrogen relative toits foam matrix. The shell is filled by exposure to hydrogen vaporduring cooling; liquid in the foam has a lower vapor pressure than freeliquid, so the shell will fill to exactly 100%. It will stay at thatfill fraction as the shell cools and the density of the liquid itcontains increases. The shell may be frozen and cooled to 4 K so that itcan be stored and handled in vacuum. When the shell is warmed, theliquid expands; the elastic modulus of the foam will force some liquidout of the surface. A simple analysis suggests that a 1 μm thickliquid film might be generated in 1 μs; that depends on thecompressibility of the foam and the flow resistance of its cellstructure. Surface tension would smooth this surface layer very rapidly.It would not begin to sag for 1000 μs, so there would be sufficienttime during which the layer would be satisfactory. An analysis will bepresented showing the feasibility of this approach, and the constraintsit puts on shell wall structure and insertion-and-shot procedures