Packaging of Superconducting Accelerator Magnet Systems

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Packaging of SuperconductingAccelerator Magnet
Systems

• Thomas H. Nicol, P.E.
• tnicol_at_fnal.gov
• http//tdserver1.fnal.gov/nicol/index.html

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Abstract
The thermal and structural considerations in the
design, analysis, and fabrication of cryostats
for superconducting magnets used in high-energy
physics applications will be described in detail
with emphasis on material selection, heat load
analysis, structural support, radiation
shielding, multi-layer insulation and internal
piping systems.
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Types of accelerator magnets
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Laboratory applications
Fermilab
Brookhaven
and others
DESY (Hamburg)
CERN (Geneva)
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Accelerator applications
Tevatron (Fermilab)
RHIC (Brookhaven)
and others
HERA (DESY)
LHC (CERN)
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Magnet applications
Tevatron (Fermilab)
RHIC prototype (Brookhaven)
and others
HERA (DESY)
LHC (CERN)
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Features common to all designs

• Beam vacuum.
• Magnet structure.
• Helium containment.
• Structural support system.
• Cryogenic piping.
• Pipe supports.
• Thermal shield(s).
• Reflective insulation (aka superinsulation or
  MLI).
• Insulating vacuum containment.
• Interconnects.

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Beam vacuum

• Beam vacuum tubes are generally round, sometimes
  oval or quadded.
• Stainless steel, preferably with low magnetic
  permeability, like 316L or 316 LN.
• Helium outside, high vacuum inside.

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Magnet structures
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More on magnet structures
LHC interaction region quadrupole (IRQ) coil
Tevatron and SSC dipole coils
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Helium containment

• Helium containment vessels are generally round,
  stainless steel tubes.
• Often pressure vessels rated at up to 20 atm (300
  psi).
• Helium, magnet structure, and beam vacuum tube
  inside.

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Structural support systems
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More on structural support systems
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More on structural support systems
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More on structural support systems

• Structural supports hold the internal assembly in
  position with respect to the vacuum vessel
  ensuring long term alignment in the tunnel.
• They resist mechanical loads introduced by
  shipping, handling, and operation.
• They insulate the cold assembly from heat
  conducted from room temperature.
• Cold masses are generally several thousand pounds
  especially in cold iron magnets, e.g. SSC
  dipole cold masses weighed 25,000 lb, LHC dipole
  cold masses weigh more than 60,000 lb.
• Heat loads can be as low as 30 to 40 mW per
  support to 4.5 K.

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More on structural support systems
LHC IRQ spider
SSC support post
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Cryogenic piping

• Internal piping provides the supply and return
  flows for shields, cooldown lines, pressure
  relief, etc.

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More on cryogenic piping
Tevatron dipole cutaway
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More on cryogenic piping
LHC IRQ piping
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Pipe supports

• Internal pipe supports provide radial positioning
  and alignment and allow axial thermal
  contraction.

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More on pipe supports
LHC IRQ pipe supports
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Thermal shields
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More on thermal shields

• Thermal shields intercept thermal radiation and
  sink it to some temperature above the magnet
  operating temperature, usually from 20 K to 80 K.
• Cooled either by LN2 or Ghe.
• Made of high thermal conductivity materials like
  aluminum or copper.

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More on thermal shields

• Design must account for thermal bowing.
• Since they are aluminum or copper, shields tend
  to shrink about 0.1 more than the magnet
  structure.

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Superinsulation
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More on superinsulation

• Superinsulation reflects radiative heat back
  toward its source.
• Effective down to about 20 K.
• Made of double aluminized mylar sheets separated
  by nylon netting, paper, crinkled aluminized
  mylar, etc.
• Typical heat transfer rates are 1.2 W/m2 for 30
  layers from 300 K to 70 K and 50 to 100 mW/m2 for
  10 layers below 70 K.

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Insulating vacuum containment
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More on insulating vacuum containment

• The insulating vacuum vessel provides the
  structural support of the internal magnet
  structure to the accelerator tunnel floor or
  magnet stands.
• It must be compatible with insulating vacuum
  levels to less that 10-6 torr with virtually no
  detectable leak.
• The insulating vacuum minimizes heat loads to the
  internal structures due to gas conduction and
  convection.
• Materials can be carbon steel, stainless steel or
  aluminum, but are usually carbon steel due to
  its low cost.

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More on insulating vacuum containment
LHC IRQ vacuum vessel
Tevatron dipole cutaway
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Interconnects

• Magnet interconnects contain all the electrical
  and mechanical connections between magnets.
• They accommodate thermal expansion and
  contraction through the use of bellows for pipes
  and expansion loops for magnet busses and
  instrumentation wiring.
• They contain shield bridges to create a
  continuous thermal shield along the length of the
  magnet string.

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More on interconnects
Tevatron dipole interconnects
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More on interconnects
LHC dipole interconnect
LHC IRQ to test stand interconnect
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More on interconnects
SSC dipole interconnect (never assume you know
all the answers..!)
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References

• Nicol, T.H., et al., SSC Magnet Cryostat
  Suspension System Design, Advances in Cryogenic
  Engineering, Vol. 33, Plenum Press, New York,
  1987.
• Nicol, T.H. and Y.P. Tsavalas, Cryostat Design
  for the Superconducting Super Collider 50mm
  Aperture Dipole Magnet, presented and Applied
  Superconductivity Conference, September 24 - 28,
  1990, Snowmass Village, Colorado.
• Nicol, T.H., SSC 50 MM Collider Dipole Cryostat
  Design, Advances in Cryogenic Engineering, Vol.
  37A, Plenum Press, New York, 1991.
• Nicol, T.H., et al., LHC Interaction Region
  Quadrupole Cryostat Design, Advances in
  Cryogenic Engineering, Vol. 47A, American
  Institute of Physics, New York, 2002.