Coining Precision Sine Wave Pattern on Lead for High Energy Density TargetJack Nguyen, Pascale Di Nicola, Cynthia Dawn Walker Panas, Sergei O Kucheyev, Chockalingam Kumar

Lawrence Livermore National Laboratory, Livermore, CA 94550

National Ignition Facility • Lawrence Livermore National Laboratory • Operated by the US Department of Energy

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Coining Tool Technology

• Coining tool consists of two main components: The upper planar die and the lower die with a sine wave

pattern. Both dies are made of steel and coated with nitride.

Die Fabrication Process

Lower die

Lead and vanadium foils

Material Preparation & Measurement

• For Rayleigh-Taylor targets, the physics package includes bonded vanadium and lead (or lead antimony)

sandwiches with interfaces thinner than ~100 nm.

• The bonded sandwich needs be mechanically robustness for subsequent coining and machining.

• We use roll-bonding to make such V/Pb and V/PbSb sandwiches.

• Cold rolling was also used to reduce Pb and PbSb films to required thickness.

Lead and Lead Antimony

Coining Ripples on Sample Materials

• Coining is an efficient way to fabricate sine wave features on lead and lead

antimony samples.

• Pattern transfer requires optimization of the force-time profile.

• Only the central section on the dual sine wave pattern is cut out and used

in the target package.

Coined Lead & Lead Antimony Samples

Machined

ripples on die

The absolute height between the lowest and highest

points on die surface should be < 250 nm

White light interferometry image

from the center area

Planar surface die

Fast Fourier Transform Analysis shows fully formed ripples with

secondary axis < 5%

White light interferometry scanning

• Hard nitride steel causes a diamond turning tool to wear out quickly.

• Nitride is brittle and can be chipped easily during machining.

• Using brass instead of nitride steel significantly reduces the failure rate and machining time. However, brass

dies are softer and, hence, require careful handling.

The upper die is

machined to match

coining materials

Bonded

vanadium lead

sample after laser

cutting

Lead and vanadium foil

Power rolling mill

• Lead or lead antimony foil is first rolled to required thickness.

• Both vanadium and lead / lead antimony are chemically cleaned.

• Stacked lead and vanadium samples are sandwiched between a stainless steel envelop before feeding into

the power rolling mill.

• Bonded sandwiches are laser cut to ~8 mm diameter discs for coining.

• Thicknesses are precisely measured by a double sided interferometer.

45 um lead foil

40 um Vanadium foil

Stainless steel envelope

Load cell

Die with the sine

wave pattern

Spherical radius

(planar) die

Foil to be coined

Spherical radius die

Dual sine waves die

Imprint ripples on sample

Remove coined product

Bonded

vanadium and

lead sample

Precision sine

wave pattern on

coined sample

Fast Fourier Transform Analysis of coining die and Pb sample

Dual sine wave pattern is fully formed

and in specification.

Roll-bonding and coining processes have been developed to manufacture Pb and PbSb components for

high-energy density physics targets. There is an ongoing process development to improve the yield and to

reduce the process time.

The Target Fabrication team at LLNL has developed processes of roll-bonding and coining of dual sine wave ripples on tantalum, lead, and lead antimony foils for Rayleigh-Taylor targets. We discuss challenges encountered in bonding and coining of Pb alloys, including coining tool fabrication and optimization of roll-bonding and pattern transfer procedures.

Roll bonded product

Lead and vanadium foils

Scanning electron microscope shows

successful bonding between vanadium and

lead

Scanning electron microscope shows

successful bonding between vanadium and

lead antimony

Vanadium

Lead Lead antimony

Bonded vanadium and lead / lead antimony are coined at room temperature.

White light interferometry measures

ripple pattern in the region of interest