Deposition of Au-Mo Cocktail Coatings and Gold-Based Thin Layers as Corrosion Protective Barrier by Magnetron Sputtering for Au-DU Hohlraums

In order to decrease the wall absorption of hohlraums during the laser-matter interaction encountered in X-ray indirect-drive inertial confinement fusion, a thick layer of depleted uranium (DU) and gold alloy can be deposited on the inner surface of the hohlraums. Such a coating can be achieved by sputtering simultaneously DU and gold directly into the hohlraums. This technique is called "moulding PVD." In order to validate the moulding PVD technique, Au/Mo cocktail layers were deposited on glass substrates by simultaneous multitarget sputtering. Molybdenum is used for deposition of cocktail alloys since it shows the same sputtering yields as uranium. Au/Mo cocktail layers can be easily grown on glass substrates at any desired composition and controlled thickness by optimizing the deposition parameters. A major issue of DU deposition is its rapid delamination in contact with water, air, or hydrogen. To protect the DU/Au alloy, a thin coating of dense gold is sputtered on the DU alloy. Dense and low-stress gold thin films deposited on glass substrates have been achieved by optimization of processing parameters. The effect of such a coating has been quantified thanks to the study of praseodymium oxidation (which is more sensitive to delamination than DU). A gold coating thickness of 0.2 m thoroughly decreases the oxidation rate of praseodymium in contact with air.