PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION

1. Developments in Sputtering Multi-Layered Depleted Uranium and Gold for use in “Cocktail” Hohlraums PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION Heather Wilkens, Abbas Nikroo,Michael Mauldin, Jason Wall, and Don Wall of General Atomics Janelle Gunther and Russell Wallace of Lawrence Livermore National Laboratory 2005 High Energy Density Physics Summer School

2. Abstract • The addition of a high-Z material like depleted uranium to the traditional gold hohlraum increases the calculated efficiency of the laser to X-ray energy conversion that takes place at the hohlraum wall [1]. Multi-layered coatings, created by rotating a substrate in front of separate DU and Au sputter sources, are being made rather than co-sputtering the material from a single source with the intent of sealing the DU in gold layers and thus slowing the process of oxidation of the DU, the purported source of lower than expected efficiency measurements from previous cocktail hohlraums [2]. Early experimental results show that the multi-layered cocktail films are resistant to oxidation, though transmission electron microscopy (TEM) images elucidate the presence of voids in some materials, and typically show that the DU and Au layers grown on a variety of different substrates are intermixed. The TEM images are shown in conjunction with results from depth-profiling Auger electron spectroscopy. • [1] T.J. Orzechowski, M.D. Rosen, H.N. Kornblum, L.J. Suter, A.R. Thiessen, R.J. Wallace, and L.J. Porter, Phys. Rev. Lett. 77, 3545 (1996). • [2] Mordy Rosen, LLNL, private comm.

3. conversion to thermal X-rays Laser scattering loss Laser entry hole (LEH) loss hohlraum wall loss Hohlraum wall opacity is optimized with the addition of a high-Z material like depleted uranium Less energy is lost to a “cocktail” wall because U fills in the Au opacity gaps

4. Au plug Dy plug Magnetron sputtering Vacuum Pump Inert Gas In Substrate DU Target Plasma Target + - HV Permanent Magnet N N S Cocktail hohlraums were previously made by co-sputtering the materials • Gold, dysprosium, and depleted uranium were sputtered from the same target position • Problems with poor performance was believed to be caused by oxidation

5. Thick Au capping layer (>2 m) Repeat multi-layers Au (8 nm) DU (30 nm) 100 nm Au under layer Problems with oxidation motivated the work on multi-layered cocktails • Oxygen drastically reduces the wall efficiency • Multi-layered films intended to encapsulate the uranium in gold, reducing the rate of oxidation • Allows more flexibility in composition • Layer thicknesses set by composition requirements

6. Sputter source 45° A coater system capable of producing multiple cocktail coatings was designed and assembled at GA • Six fixed guns • Six rotating part holders • Parts rotate at a 45º angle in front of sputter sources

7. 1 mm Free-standing, low-stress cocktail cylinders are now being produced repeatedly Low-stress sputtered cocktail coating Electroplated gold for structural integrity Back-machined to size with dedicated lathe Acrylic mandrel leached away in acetone

8. 1 mm Parts were sent to national labs for experiments after only four months of operation This cocktail cylinder was shot at the OMEGA laser facility in Rochester, New York: “…this cocktail barrel is the highest Tr ever for a "cylinder only" cocktail hohlraum! It is only one data point, but this is extremely promising.” - Ogden Jones, LLNL

9. 50 nm Au/(30 nm U/6 nm Au)x40/50 nm Au Uranium Gold Oxygen Auger spectroscopy of cocktails deposited on flat substrates indicates low oxygen content Deposited on Si substrate Goal: <10% O • 75 at% DU:25 at% Au targeted composition • Clear signs of intermixing • Low oxygen content

10. Goal: <10% O Oxygen peaks at ~10 & ~20 nm uranium oxygen Analysis of oxidized uranium confirms low oxygen content in cocktail materials Depleted uranium thin film O at ~20 nm O at ~60 nm Cocktail foil Proton backscattering spectrometry (PBS) confirms ~5% oxygen in the bulk

11. U Au Intermixing 100 nm 50 nm Transmission electron microscopy confirms the presence of intermixed layers Target: 30 nm DU/8 nm Au multi-layers Deposited on flat silicon substrate • Layers are flat and persist over long distances • Some U layers crystallographically different than others (bright/dark) All TEM images thanks to Jennifer Harper of LLNL

12. 20 nm 20 nm Free-standing films show layer undulation not seen in coatings on Silicon Target: 30 nm DU/8 nm Au multi-layers Deposited on stretched cellulose acetate film then released in acetone Degree of intermixing changes as a function of layer position within the stack

13. Uranium Gold Oxygen Goal: <10% O voids 200 nm Cocktail coating on aluminum mandrel displays ripples, intermixing, and voids Targeting: 50 nm Au/(30 nm U/8 nm Au)x10/50 nm Au Deposited on rotating Al mandrel • TEM image confirms large degree of intermixing inferred from Auger data • Slightly higher O content than coatings on flat substrates

14. Sputtered multi-layered cocktail coatings are being made and characterized in collaboration with LLNL • Depleted uranium and gold cocktail increases the conversion efficiency of hohlraum walls • Multi-layer coatings are being used to fabricate cocktail hohlraums • Auger electron spectroscopy (at GA) and transmission electron microscopy (at LLNL) are used to characterize the cocktail materials • composition √ • morphology √ • uniformity

15. Acknowledgments • Work supported by U.S. Department of Energy under Contracts DE-AC03-01SF22260 and W-7405-ENG-48 • Special thanks to Jennifer Harper at Lawrence Livermore National Laboratory for the high quality TEM images presented in this poster