Mechanical Injection Accuracy

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Mechanical Injection Accuracy

• Presented by Ron Petzoldt
• Dan Goodin, Emanuil Valmianski, Landon Carlson
  and Bertie Robson
• ORNL HAPL meeting
• March 21-22, 2006

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Good news for target injection
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• Dramatically improved (best-ever) injection
  accuracy for very low mass projectiles
• New magnetic slingshot offers further
  improvement
• Evaluated in-flight steering systems as backup to
  enhance accuracy

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Gas gun injection has several sources of position
error

• Sabot vibration in barrel
• Target vibration in sabot
• Sabot separation
• Target separation from sabot
• Gas turbulence

Shuttle
Pneumatic driver
Magnetic driver
Reducing injection speed from 400 m/s to lt100 m/s
allows possibility of mechanical or magnetic
injection without sabot separation and gas
turbulence
Shuttle
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Careful control of positioning and stability was
required to achieve accuracy with mechanical
injection
Target rolls back into seat and rolls around
Desired, stable position
Long target shuttle with tight fitting bands
reduces vibration
Target seat
Careful control of target seat required - foam
seat used to stop vibrations
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A single-shot mechanical injection device was
built and tested
Spring (crossbow) provides driving force
Stopping sheeve
Captive shuttle extension
Shuttle guide
Vacuum seal
Vibration damping
Vacuum Chamber
Accelerator/De-accelerator
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Substantial target injection accuracy improvement
achieved
Injection method Target Material Mass 4 m, 1 ? accuracy 17 m, 1 ? Extrapolation
Gas gun best results 10-20 mTorr Plastic Steel 30 mg 300 mg NA 10 mm 7.5 mm
Mechanical 300 mTorr Steel 300 mg 0.2 mm 0.85 mm
Mechanical 300 mTorr Solid plastic 30 mg 1.0 mm 4.2 mm
Mechanical 300 mTorr Hollow plastic 1 mg 1.2 mm 5.1 mm
Mechanical 10-20 mTorr with reduced static charge Hollow plastic 1 mg 0.9 mm 3.8 mm
Mass of an IFE target is about 8 mg
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Mechanical injectors can be built using a
number of driving sources
Magnetic slingshot
Coil gun
Pneumatic
Overcomes many challenges of mechanical injector
such as mechanical feed throughs
Geared Crank or Cam
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Magnetic slingshot concept can provide accurate
low-speed injection
Hmax
H0
Shuttle apogee
Conducting tube
Ferromagnetic shuttle is accelerated through
increasing field and slows through decreasing
field
Target separation
S/C Coil
Bertie Robson THE MAGNETIC SLINGSHOT A LOW
VELOCITY TARGET INJECTOR 12 March 2006
Trigger coil OFF
Shuttle

Trigger coil ON
Trigger coil
Powder iron or Metglas
Nonmagnetic disk
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Shuttle can be stabilized by conducting tube
Stabilizing eddy currents
Allows non-contact, frictionless operation
m-
m
Shuttle off center in tube
r0
An integral number of half oscillations will
maximize injector accuracy
Case (a)
r0

Case (b)
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Maximum speed is 60-80 m/s
16 T max field Nb3Sn superconductor gives 86 m/s

• Magnetic slingshot concept has several advantages
• Utilizes non-contacting ferromagnetic shuttle
• No friction wear
• Centering force provided by conducting enclosure
• No sabot or gas turbulence
• Potentially very accurate
• No mechanical feedthroughs required into
  cryostat
• Powered via simple DC magnetic field

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If needed, in-flight steering can be achieved
with very reasonable parameters
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Charge can be induced onto the target passing
into a negative potential region
-4 kV
0 V
Voltage Source
Vacuum wall
Gun Barrel
Conducting carbon fiber pushrod
Target
Insulating pushrod
Not to Scale!
Barrel sleeve (insulated conductor)
Target charging with mechanical injector
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Model shows adequate target charge is achievable
Vacuum ? 1
Target Radius 2mm
Dielectric ? 2
ANSYS model
Close up
Potential distribution (?V 4 kV)
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Summary

• Target position placement accuracy dramatically
  improved
• ? 3.8 mm for 1 mg shells and 0.85 mm for steel
  spheres (extrapolated to 17 m)
• New magnetic slingshot injector concept
  overcomes many key design challenges of
  mechanical injection.
• In-flight steering could be used to further
  improve target injection accuracy