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Nb3Sn Magnet Development Breakthrough. Alexander Zlobin Technical Division, Fermilab. Introduction. Nb3Sn vs. NbTi Bc2~28T (NbTi: 14T) => higher operation fields Tc~18K (NbTi: 9K) => larger temperature margin Jc(12T)~3 kA/mm2 (=Jc(5T) NbTi) => efficient coils Issues

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nb3sn magnet development breakthrough

Nb3Sn Magnet Development Breakthrough

Alexander Zlobin

Technical Division, Fermilab


Nb3Sn vs. NbTi

  • Bc2~28T (NbTi: 14T) => higher operation fields
  • Tc~18K (NbTi: 9K) => larger temperature margin
  • Jc(12T)~3 kA/mm2 (=Jc(5T) NbTi) => efficient coils


  • Nb3Sn is brittle material sensitive to stress and strain => special materials, fabrication technologies, handling, coil support during operation
  • Nb3Sn strands are unstable wrt “flux jumps” due to large Jc and Deff => conductor optimization

Nb3Sn accelerator magnet development

  • started in 70’s (BNL, Saclay)
  • last 10 years centered in U.S. => magnets: LBNL, Fermilab, BNL, TAMU; conductor: Labs, universities, industry)
  • Focused R&D + Adequate resources + Enthusiasm => breakthrough in Nb3Sn magnet development


Nb3Sn Magnet Development Breakthrough

nb3sn coil technology
Nb3Sn coil technology

1m Q coils


  • W&R approach (reaction at ~650C during ~50 hrs)
  • high-temperature insulation – ceramic, S2 or E-glass
  • metallic coil components – water-jet method
  • ceramic binder – critical invention
  • coil vacuum impregnation with epoxy
  • coil size control – field quality

Coil production:

  • 20 dipole and 34 quadrupole 1-m long coils
    • Good size reproducibility
    • Short fabrication time
  • 2 dipole and 11 quadrupole 4-m long coils
    • Technology scale up

Handling and test:

  • Multiple reassembly without degradation with different structures
  • Coil and magnet handling and transportation across the country

=> Production quality Nb3Sn coil technology!

4m D coil


Nb3Sn Magnet Development Breakthrough

mechanical structures
Mechanical structures
  • Coil pre-load and support reduce turn motion
  • Large Lorentz forces + Stress limit for Nb3Sn cable (150 MPa) => possible degradation during assembly and operation of brittle Nb3Sn coils
  • Model magnets (D and Q) were assembled and successfully tested with three different structures!
    • good performance of collar-based structure => solid base for accelerator quality Nb3Sn magnets!

SS shell w/o collar (FNAL-HFDA)

Al shell w/o collar (LBNL-TQS)

SS shell + SS collar (FNAL-TQC)


Nb3Sn Magnet Development Breakthrough

nb3sn strand optimization
Nb3Sn strand optimization
  • Conductor determines the SC magnet performance
  • Stable, high Jc Nb3Sn strand (RRP-108/127 with increased spacing) has been developed by Fermilab and OST
  • RRP-108/127 TQ coil successfully tested in quadrupole mirror
    • first time demonstration of stable operation at 4.5 and 1.9 K
    • Bmax~12 T (4.5K) and ~13 T (1.9K)

=> RRP-108/127 is baseline conductor for 11T Nb3Sn magnets!


Nb3Sn Magnet Development Breakthrough

  • Most important breakthroughs
    • Development of production-quality Nb3Sn coil technology
    • Demonstration of collar-based mechanical structures
    • Development of high-performance Nb3Sn strand

=> accelerator-quality Nb3Sn magnets (D and Q)

  • Fermilab HFM program made key contributions to all these breakthroughs
  • 10-11 T accelerator quality Nb3Sn magnets are real and can be considered now for practical applications
  • Solid base for higher field (~15 T) Nb3Sn accelerator magnets needed for Muon Collider and some other applications


Nb3Sn Magnet Development Breakthrough