AVS 53rd International Symposium
    Thin Film Tuesday Sessions
       Session TF-TuP

Paper TF-TuP14
Multi-layered Depleted Uranium and Gold Coatings on Cylindrical Substrates

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Thin Film Poster Session
Presenter: H. Wilkens, General Atomics
Authors: H. Wilkens, General Atomics
J.L. Klingmann, Lawrence Livermore National Laboratory
A. Nikroo, General Atomics
D.R. Wall, General Atomics
J.R. Wall, General Atomics
Correspondent: Click to Email
The indirect drive approach to inertial confinement fusion (ICF) requires that a hydrogen-filled target capsule is surrounded by a cylindrical cavity called a hohlraum which converts the incident laser energy to x-rays that drive the implosion of the target.@footnote 1@ The efficiency of the x-ray conversion increases with the addition of depleted uranium (DU) to a Au-only hohlraum by making the wall more opaque to the driver energy.@footnote 2@ To manufacture these hohlraums, multiple alternating layers of 30 nm DU and 8 nm Au are sputter deposited onto rotating cylindrical substrates, for a total thickness of 2-7 µm.@footnote 3@ These cylindrical substrates, 5.1 mm in diameter, are micro-machined to less than 25 nm rms roughness. A structural gold layer is electroplated after sputter deposition, then the material is back-machined away at the edges to expose the underlying mandrel, which is leached away leaving a free-standing hohlraum. DU oxidizes rapidly in air (0.5 nm/min),@footnote 4@ so measures must be taken to ensure that it is encapsulated. Oxidation is problematic for two reasons. First, the presence of oxygen in the hohlraum increases the heat capacity, thus canceling the efficiency gains made with the addition of the DU. Second, the DU lattice increases by approximately a factor two upon oxidation, resulting in catastrophic structural failure. Novel production techniques will be presented, along with Auger electron spectroscopy data confirming the absence of oxygen within the multi-layered film. @FootnoteText@ @footnote 1@ Rosen, M., Phys. Plasmas, 6, 1690 (1999).@footnote 2@ Orzechowski, T., et al., Phys. Rev. Lett. 77, 3545 (1996).@footnote 3@ Wilkens, H., et al., Progress in Coating Multi-layered Cocktail Hohlraums. To be published in Fus. Sci. Technol.@footnote 4@ Allred, D., et al., Highly Reflective Uranium Mirrors for Astrophysics Applications, X-ray Mirrors, Crystals and Multilayers, Proc. SPIE 4782, 212, 2002.