The LHC magnet R&D program has shown that the limit of NbTi technology at 1.9 K was in the 10-to-10.5-T range. Hence, to go beyond the 10-T threshold, it is necessary to change the superconducting material. Given the state of the art in HTS, the only serious candidate is Nb 3 Sn. A series of dipole magnet models built at Twente University and LBNL as well as a vigorous program carried out at Fermilab have demonstrated the feasibility of Nb 3 Sn magnet technology. The next step is to bring this technology to maturity, which require further conductor and conductor insulation development and a simplification of manufacturing processes. After a brief history, we review ongoing R&D programs in Europe and we present the Next European Dipole (NED) initiative promoted by the European Steering Group on Accelerator R&D (ESGARD). Index Terms-Accelerator magnets, LHC upgrade, Nb 3 Sn superconductor. I. INTRODUCTION T HE CERN/LHC superconducting magnet R&D program was successful in developing a design suitable for industrial production [1], but it demonstrated also that the limit of accelerator magnets wound from binary NbTi conductors and operated in superfluid helium at 1.9 K lied in the 10-to-10.5-T range. Presently, the best performing (binary) NbTi dipole magnets are: (1) a 1-m-long, 50-mm-twin-aperture LHC model, referred to as MFISC [2]; and (2) a 1-m-long, 88-mm-single-aperture model, referred as MFRESCA [3]. MFISC was designed by a team led by D. Leroy in collaboration with the Helsinki University of Technology. It was built and cold tested at CERN and reached (in a few quenches) a record magnetic flux density of 10.53 T at 1.77 K. MFRESCA was designed also by a team led by D. Leroy, but was built by HMA Power Systems in the Netherlands. It is now implemented in the CERN cable test facility and is operated routinely up to 10 T (note that, at this field level, the Lorentz forces developed in the MFRESCA coils are about twice those developed in regular LHC dipole magnet coils Manuscript
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