PERSISTENT SURVEILLANCE FORPIPELINE PROTECTION AND THREAT INTERDICTION

Micromachining of Inertial Confinement Fusion Fast Ignition

TargetsMichael Mauldin

Annette GreenwoodMelissa Kittelson

Clyde ShearerJoe Smith, Jr.

David Woodhouse

2005 HEDP Summer SchoolBerkeley, CaliforniaAugust 7-12, 2005

Fast ignition targets consist of a GDP shell that sits on the tip of a gold cone

• Hollow GDP Shell– Less than 1 mm outside radius – Approximately 20 µm wall

• Hollow Gold Cone– Various cone angles– Cone length ~5 mm– Tip wall thickness ~30 µm – Hyperboloid tip on outside of cone

• Assembly of shell and cone– Cone tip 40 µm from shell center along cone axis,

+10 µm along the axis, +5 µm perpendicular to cone axis

Computer Model of FI Target

Cross Section View and Specifications for Fast Ignition Target Tip

860 + 20 µm

40 + 10 µm

Overview of Steps to Create Targets

• Machining the copper mandrel• Gold plating the mandrel• Cutting a hole in the shell• Machining the gold cone to fit the shell• Etching out the copper mandrel• Assembling the target

Machining and Gold Plating of a Copper Mandrel

• Mandrel Makes the Inner Profile of the Target Cone

• Multiple Steps to Create Mandrel– First Use CNC Lathe

• A cylinder is cut from stock copper rod– Diamond Turning Lathe Cuts Final

Shape• 25 µm radius diamond tool forms cone

to desired dimensions• 5 µm radius diamond tool makes final

cuts for optimal finish• Length of copper mandrel must be

recorded for future back machining

• Plate ~120 µm gold over entire cone

Copper Mandrel after Machining

5mm

Machining of a GDP Shell for Target

• Glow discharge polymer (GDP) shell is made on PAMS* mandrel and mandrel is removed by thermal depolymerization and diffusion

• Must Cut Hole Of Proper Dimension– Shell is glued onto glass slide for

placement on lathe’s vacuum chuck– Dimensions of shell, desired cone tip

position in relation to center of shell, and final cone are used to calculate depth of cut

– Dimensions of hole and shell are accurately measured after cut

~225 µm diameter hole

*poly-alpha methylstyrene

Back-Machining of the Gold Plated Cone

• Shelf must be cut into Gold Plated Copper Cone on Diamond Turning Lathe– Cone must be centered on

spindle to ensure gold thickness around cone is uniform after cutting

– Copper mandrel measurements are used to calculate amount of gold to be removed

– Shelf is cut into gold layer of cone

Illustration of Gold Cone Shelf

Each cone is created to fit a specific shell that has been cut

• Gold shelf must be cut into cone so the shell sits at the correct height – Shelf height for each cone tip can be adjusted to ensure

tip is at correct position in relation to the shell center– Error in the vertical offset between the cone tip and

shell center are reduced when the target is assembled

• Three Possible Cases for Cone/Shell Fit on Gold Shelf– No space between the shell hole and base of cone– Space between the shell hole and base of cone– Base of cone is larger than the shell hole

• In this case, the base of the cone must be machined to allow the shell to properly sit on gold shelf

Examples of Possible Cone/Shell Fit Combinations

• A shell with a hole smaller than cone base on the shelf– Base of cone is turned down to

cylinder so shell will fit onto shelf for desired position

• A shell with a hole bigger than cone base at the shelf– Results in a gap on the shelf between

cone and shell allowing for movement

Gap

Altered outer cone profile

Assembly of Matching Cone and Shell Pairs

• Copper mandrel is etched away by Nitric Acid solution prior to assembly

• Cone and shell are assembled– Faced off shell hole surface must

fit on shelf of gold cone– Shell is placed onto cone and

manipulated into place under microscope

– Shell is centered on cone to meet given specifications

– Bead of glue is placed around joint to secure shell’s position

• Extra glue may be necessary for gas tight targets

Cone/Shell Assembly Station

Finished Fast Ignition Target

• Examples of Two Types of Completed ICF Fast Ignition Targets

34° Cone Target 70° Cone Target

Fast Ignition Targets are consistently produced within given specifications

• Characterization of assembled fast ignition targets shows that our fabrication of targets is repeatable and the critical measurements are kept within tight specifications – Critical Measurements Include:

• Shell Outer Radius and Wall Thickness (+10 µm)• Thickness of Shell Wall (+2 µm)• Vertical Offset - Axial distance between cone tip and shell

center (+10 µm)• Horizontal Offset - Radial distance between cone tip and

shell center (+10 µm)

• New techniques in the machining of each cone to fit a specific shell creates more consistent and efficient target fabrication