Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Hybrid magnet
Hybrid magnets, the combination of a resistive inner coil with a superconducting outer one, allow to
generate the highest continuous magnetic fields for a given electrical power installation. The present
state-of-the-art hybrid magnet system has been built by the NHMFL at Tallahassee in Florida and has
produced the highest DC magnetic field equal to 45.2 T in a 32 mm bore.
Table 1 : Hybrid magnets and projects with continuous field higher than 35 T in the world
Place Magnetic field Remarks
Tsukuba, Japan 35 T = 14 T (Nb3Sn) + 21 T (15 MW) Operational
Tallahassee, US 45 T = 11 T (Nb3Sn) + 34 T (30 MW) Operational
Grenoble, France 42 T = 8.5 T (NbTi) + 33.5 T (24 MW) Planned for 2013
Nijmegen, The Netherlands 42 T = 12 T (Nb3Sn) + 30 T (20 MW) Planned for 2013
Hefei, China 42 T = 11 T (Nb3Sn) + 29 T (20 MW) Planned for 2013
Tallahassee, USA 36 T = 14 T (Nb3Sn) + 22 T (12 MW) Planned for 2012
Unfortunately, the last hybrid coil project of LNCMI-G, aiming to produce 40 T, failed
because of a defect in the superconducting outsert coil produced in industry. In order to maintain the
competitiveness and attractiveness of the LNCMI-G it was decided end of 2006 to replace the outsert
coil instead of fully restarting a new project, mostly because of the shorter delivery time scale. The
base-line for the coil sub-assemblies of the hybrid magnet is given in Table 2 together with their
magnetic field contributions. Ultimately, the field produced by the poly-helix and Bitter coils is
planned to be further increased, typically up to 36-37 T, which should allow for a 43-44 T hybrid
magnet.
Table 2 : Composition of the 42T hybrid magnet
Hybrid subpart Magnetic Field
14 series connected helix coils 24.5 T
2 series connected Bitter coils 9 T
1 superconducting pancake coil 8.5 T
Table 3 : Main parameters of the superconducting outsert coil
Characteristics Values
Inner/outer radius 550/913 mm
Height 1400 mm
Inductance 3 H
Nominal current (8.5 T) 7100 A
Stored Energy 76 MJ
Operating Temperature 1.8 K
A conceptual study for the new superconducting outsert of the hybrid coil project has been
prepared in collaboration with IRFU-CEA, and reviewed by internal and external experts. The most
important choices that have been made can be summarized in five key points:
- High current to minimize the coil self-inductance and reduce voltage levels during quenches,
- Nb-Ti superconductor at 1.8 K,
- Vacuum impregnated coil with internal cooling,
- Insulated conductor to increase the safety and reliability,
- A 30 K copper screen with stainless steel reinforcement to absorb a part of the induced field
effects in case of sudden loss of the power of the resistive coils.
The already existing infrastructure of the hybrid magnet has fixed the maximal dimensions of the
superconducting coil, which are listed in Table 3 together with the main parameters. To produce a
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