Gradient Coating for NIF Double Shell Targets

As opposed to a single shell, the double shell target design provides an alternative implosion platform for high energy density (HED) experiments at the National Ignition Facility (NIF) and related laboratories. The inner shell of this target scheme incorporates a density graded layer to suppress inhomogeneity induced Rayleigh-Taylor instabilities during the implosion. Here we report our efforts to fabricate density graded layers for use as the inner shell of a double shell target using magnetron sputtering as well as the characterization of these layers. Cold welding (spherical targets sticking to either each other or the deposition pan) was observed for many of metals surveyed and seems to be correlated with material ductility. A W-Be gradient layer was successfully fabricated as an inner shell. This material combination is advantageous due to the constituent's large inherent density difference. Microstructural changes are revealed with varying composition including a previously unknown amorphous phase.