# Presentation: 658459

## Packaging of SuperconductingAccelerator Magnet Systems

- Thomas H. Nicol, P.E.
- _[tnicol@fnal.gov](mailto:tnicol@fnal.gov)_
- _[http://tdserver1.fnal.gov/nicol/index.html](http://tdserver1.fnal.gov/nicol/index.html)_

## 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.

## Types of accelerator magnets...

## Laboratory applications...

- Fermilab

- DESY (Hamburg)

- Brookhaven

- CERN (Geneva)

- and others...

## Accelerator applications...

- Tevatron (Fermilab)

- RHIC (Brookhaven)

- HERA (DESY)

- LHC (CERN)

- and others...

## Magnet applications...

**Magnet applications...**

- Tevatron (Fermilab)

- RHIC prototype (Brookhaven)

- HERA (DESY)

- LHC (CERN)

- and others...

## 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.

## 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.

## Magnet structures...

## More on magnet structures...

- Tevatron and SSC dipole coils

- LHC interaction region quadrupole (IRQ) coil

## 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.

## Structural support systems...

## More on structural support systems...

## More on structural support systems...

## 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.

## More on structural support systems...

- SSC support post

- LHC IRQ spider

## Cryogenic piping...

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

## More on cryogenic piping...

- Tevatron dipole cutaway

## More on cryogenic piping...

- LHC IRQ piping

## Pipe supports...

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

## More on pipe supports...

- LHC IRQ pipe supports

## Thermal shields...

## 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.

## 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.

## Superinsulation...

## More on superinsulation...

- Superinsulation reflects radiative heat back toward it’s 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.

## Insulating vacuum containment...

## 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 it’s low cost.

## More on insulating vacuum containment...

- Tevatron dipole cutaway

- LHC IRQ vacuum vessel

## 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.

## More on interconnects...

- Tevatron dipole interconnects

## More on interconnects...

- LHC dipole interconnect

- LHC IRQ to test stand interconnect

## More on interconnects...

- SSC dipole interconnect (never assume you know all the answers..!)

## 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.