In this article the authors describe the present situation and future developments of the hybrid magnets at the High Magnetic Field Laboratory in Grenoble. They specify the condition under which the 30T, 50mm-diameter now in service is operated, and describe the projects for hybrid magnets which could be constructed in the years to come. A magnet generating over 40T should be operational within three years; it would be built economically, and the magnetic field from the superconducting element would contribute less than 10T. A considerably more powerful magnet generating a continuous magnetic field of 50T is under consideration for later.
Multifilamentary Nb3Sn composite conductors with submicron filament diameters have been developed by the internal tin diffusion method. The heat treatment condition to optimize the critical current density was studied in detail. The different heat treatment was performed in two stages according to the arrangement of the copper clad tin cores in strands. The first stage is for the homogenization heat treatment (HHT) of tin in the copper matrix. In the second stage, the reaction heat treatment (RHT) of Nb3Sn was applied. With a suitable combination of HHT and RHT, Nb3Sn with a critical current density high enough for a.c. use was formed at a reaction temperature as low as 350°C.