Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

- for B > 80 T in the coilin/coilex system: the development of Cu/SS wires, for the coilin, with 60% of SS
(UTS>1550 MPa) and a cross section of 2.00*1.25 mm 2 allows to reach 81T (the LNCMI record) in spring 2009.
- for coil aging study within DENUF project (FP6): the study of the influence of the work-hardening on
Cu/SS macrocomposite wires has been performed in order to determine the best compromise between strength
and plastic strain with respect to the coil lifetime. Several small batches (50 meters) with different workhardening
ratio (RA= 65, 70, 75%, 80%) have been elaborated in-house and insulated by an industrial company
with a double layer of polyimide films (Kapton).
Research & Development of high strength composite conductors
- Cu alloys for magnets with optimized current distribution: conductors made of Cu alloys like GlidCop
(CuAl2O3) or CuAg (with low silver content 0.08%) have been provided by industrial companies in order to be
combined with Zylon fibers in magnet with optimized reinforcement distribution.
- CuNbTi microcomposite wires for conventional magnets and split-coil:
A strong link has been developed with the industrial company MSA in order to adapt commercially available
“raw materials” to the specifications of high pulsed field magnets. CuNbTi wires have been provided by MSA.
First, a selection of round samples from LHC production has been characterized in liquid nitrogen at LNCMP.
The good level of mechanical properties (UTS>1GPa at 77K) promotes them as potential candidates for pulsed
magnets. Rectangular cross sections of 2.00mm * 3.15mm have been transformed.
Coil aging studies on CuSS and CuNbTi minicoils
In the framework of the European project DeNUF, “new” conductors and “new” insulators have been
systematically aged using the mini-coil aging platform. During the period 2005-2009, we have performed aging
experiments on CuSS (LNCMP), CuNbTi (MSA) mini-coils and also on in-situ CuNb wires provided by HLD
(Dresden) and Bochvar Institute (Moscow).
Mini-coils wound with CuSS and CuNbTi have been tested in order to compare their aging performances. We
have also compared two materials for insulation: polyester fibers and Kapton ribbons. Moreover, wet winding
impregnation (LNCMP) and vacuum impregnation, performed in the Clarendon Laboratory (University of
Oxford), were applied to the polyester insulated mini-coils.
Three CuNbTi coils, wet wound with polyester fiber braiding insulation, have shown electrical damages after
winding. We observe an improvement by applying vacuum impregnation but the two coils have been damaged at
low fields (4.7 and 13.8 T) due to an electrical failure. Two others coils insulated with Kapton ribbons have been
successfully tested until a maximum field of 36.5 T and aged at 33.8 T (92%Bmax). The insulation method
which is suitable to the obtention of high magnetic field is the Kapton insulation.
The electrical resistance monitoring data, for the CuNbTi wires insulated with Kapton, are compared to the ones
of the CuSS wires. Bmax for the CuNbTi coils is comparable to the CuSS coils near 36 T. The increase of
electrical resistance before the coil failure is much more important for CuNbTi (+15%) than CuSS (+5%). We
can link this difference to the fact that the Cu matrix embedding NbTi filaments is free to deform whereas in
CuSS wires, the deformation of the copper core is constrained by the stainless steel jacket. The same behaviour
is observed during aging.
Nevertheless during aging after 60 shots at 92%Bmax, the resistance of the CuNbTi coil suddenly increases by
8%. The total resistance variation reaches 25% after 60 shots. The plastic aging of the CuNbTi coils seems to be
more rapid than the plastic aging of CuSS coils , where �R= 9% after 100 shots (or even more) at 90%B max.
The CuNbTi conductors are well adapted to generate high magnetic field, but their aging performances at high
field are weaker than the CuSS conductors.
Mini-coil wound with polyester insulated CuNbTi
14