IFT/P2005-076

PERSISTENT SURVEILLANCE FORPIPELINE PROTECTION AND THREAT INTERDICTIONHeather Wilkens, Abbas Nikroo, Michael

Mauldin, Jason Wall, and Don Wallof

General Atomics

Janelle Gunther and Russell Wallaceof

Lawrence Livermore National Laboratory

2005 High Energy Density Physics Summer School

Developments in Sputtering Multi-Layered Depleted Uranium

and Gold for use in “Cocktail” Hohlraums

IFT/P2005-076

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.

IFT/P2005-076

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

wall loss

Laser entry hole (LEH) lossLaser scatteringloss

hohlraum

conversion to thermal X-rays

1000

104

105

106

0.1 1

AuU

Cold Opacity

(cm2/

g)

E (keV)

IFT/P2005-076

Cocktail hohlraums were previously made by co-sputtering the materials

+ -

Vacuum Pump Inert Gas InSubstrate

N NS

Permanent Magnet

Target

HV

Plasma

Magnetron sputtering

•Gold, dysprosium, and depleted uranium were sputtered from the same target position

•Problems with poor performance was believed to be caused by oxidation

DU Target

Au plug

Dy plug

IFT/P2005-076

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

Repeat multi-layers

100 nm Au under layer

Thick Au capping layer (>2 m)

DU(30 nm)

Au (8 nm)

IFT/P2005-076

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

Sputter source

45°

IFT/P2005-076

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

1 mm

IFT/P2005-076

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

1 mm

IFT/P2005-076

Auger spectroscopy of cocktails deposited on flat substrates indicates low oxygen content

50 nm Au/(30 nm U/6 nm Au)x40/50 nm Au

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Depth (nm)

Atomic %

Oxygen

Uranium

Gold

•75 at% DU:25 at% Au targeted composition

•Clear signs of intermixing•Low oxygen content

Deposited on Si substrate

Goal:

<10% O

IFT/P2005-076

Analysis of oxidized uranium confirms low oxygen content in cocktail materials

Depleted uranium thin film

-1200

-800

-400

0

400

800

1200

500 505 510 515 520

Kinetic energy (eV)

N(E)

0

20

40

60

80

100

0 20 40 60 80 100

Depth (nm)

Atomic %

uranium

oxygen

O at ~20 nmO at ~60 nm

Cocktail foil

-1200

-800

-400

0

400

800

1200

500 502 504 506 508 510 512 514 516 518 520

Kinetic energy (eV)

N(E)

Oxygen peaks at ~10 & ~20 nm

Proton backscattering spectrometry (PBS) confirms ~5% oxygen in the bulk

Goal:

<10% O

IFT/P2005-076

Transmission electron microscopy confirms the presence of intermixed layers

Target: 30 nm DU/8 nm Au multi-layers Deposited on flat silicon

substrate

100 nm

• Layers are flat and persist over long distances

• Some U layers crystallographically different than others (bright/dark)

UAu

50 nm

Intermixing

All TEM images thanks to Jennifer Harper of LLNL

IFT/P2005-076

Free-standing films show layer undulation not seen in coatings on Silicon

Target: 30 nm DU/8 nm Au multi-layersDeposited on stretched cellulose acetate film then released in

acetone

Degree of intermixing changes as a function of layer position within the stack

20 nm 20 nm

IFT/P2005-076

Cocktail coating on aluminum mandrel displays ripples, intermixing, and voids

Targeting: 50 nm Au/(30 nm U/8 nm Au)x10/50 nm AuDeposited on rotating Al

mandrel

200 nm

voids

•TEM image confirms large degree of intermixing inferred from Auger data

•Slightly higher O content than coatings on flat substrates

0102030405060708090

100

0 50 100 150 200 250 300 350 400

depth (nm)

atomic %Oxygen

Uranium

Gold

Goal: <10%

O

IFT/P2005-076

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

IFT/P2005-076

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