Conductor R&D for the Iseult/INUMAC Whole Body 11.7 T MRI Magnet

As the design of the Iseult/INUMAC 11.7 T MRI magnet involves new technical solutions using NbTi conductors (due to its larger dimensions), we developed a conductor R&D plan. Only the main coil conductor of this shielded magnet is covered by this R&D. Three types of design (monolith, cable in channel and cable around a copper core) have been developed by CEA and ALSTOM MSA. The main coil prototype conductors will have a minimum critical current of 1,500 A at 12 T and 2.8 K. Due to the unusual specified temperature, we translated the requirements to industrial standards (2,591 A at 9.5 T and 4.22 K taking into account 5% margin drop for R&D). The main characteristics of the conductor are firstly that it must have very precise and reproducible dimensions (tolerances lower than 15) to enable the magnetic field homogeneity. Secondly, it must attain simultaneously a low electrical resistance (20 mu Omega / m at 10 K and 12 T) and a high mechanical strength (sigma(0.2%) > 250 MPa). The aims of the industrial development are to validate the conductor performance obtained in the design conditions, especially critical current and conductor behavior during coil manufacturing. Several lengths have been produced for the 3 design types. The conductor prototypes are fully characterized by mechanical, electrical and geometrical measurements. From these results, several criteria enable selection of the most efficient conductor type.