Micromachining of Inertial Confinement
Fusion Fast Ignition Targets
PERSISTENT SURVEILLANCE FOR
PIPELINE PROTECTION AND THREAT INTERDICTION
Michael Mauldin
Annette Greenwood
Melissa Kittelson
Clyde Shearer
Joe Smith, Jr.
David Woodhouse
2005 HEDP Summer School
Berkeley, California
August 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
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Various cone angles
Cone length ~5 mm
Tip wall thickness ~30 µm
Hyperboloid tip on outside of cone
Computer Model of FI Target
• 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
Cross Section View and Specifications for Fast
Ignition Target Tip
860 + 20 µm
40 + 10 µm
Overview of Steps to Create Targets
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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
5mm
– 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
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 bigger than cone
base at the shelf
– Results in a gap on the shelf between
cone and shell allowing for movement
Gap
• 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
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