PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION Micromachining of Inertial Confinement Fusion Fast Ignition Targets 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 –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 µm 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 Target70° 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