The Next European Dipole (NED) Joint Research Activity was launched on 1st January 2004 to promote the development of high performance Nb 3 Sn conductors in collaboration with European industry (aiming at a non-copper critical current density of 1500 A/mm 2 at 4.2 K and 15 T) and to assess the suitability of Nb 3 Sn technology to the next generation of accelerator magnets (aiming at an aperture of 88 mm and a conductor peak field of ~ 15 T). It is part of the Coordinated Accelerator Research in Europe (CARE) project, involves eight collaborators and is half-funded by the European Union. After briefly recalling the Activity organization, we report the main progress achieved over the last year, which includes: the manufacturing of a double-bath He II cryostat for heat transfer measurements through Nb 3 Sn conductor insulation, detailed quench computations for various NED-like magnet configurations, the award of two industrial subcontracts for Nb 3 Sn conductor development, the first results of a cross-calibration program of test facilities for Nb 3 Sn wire characterization, detailed investigations of the mechanical properties of heavily cold-drawn Cu/Nb/Sn composite wires and the preliminary assessment of a new insulation system based on polyimide-sized fiber glass tapes. Last, we briefly review the efforts of an ongoing Working Group on magnet design and optimization.

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Electrical insulation is one of the most challenging issues governing the engineering exploitation of niobium-tin conductors. This is especially true for future accelerator magnets manufactured by the "wind-and-react" route. Applications such as the LHC Interaction Region upgrade or in the longer term an LHC energy upgrade will require magnets to operate at high fields in demanding thermal and radiation environments. The Next European Dipole (NED) programme is aimed at the development of a large aperture (up to 88mm) high field (up to 15T conductor peak field) superconducting dipole magnet relying on niobium-tin conductors. Conventional insulation development is being addressed in two key areas, the engineering requirements for large scale magnet manufacture and the improvement of materials properties for magnet operation and performance. The paper will review the status of insulation technology for niobium-tin accelerator magnets and define the special requirements for NED. Particular emphasis will be placed on the development of fibre sizing technology and its influence on magnet manufacture and electrical/mechanical performance of insulation laminates. This work is supported in part by the European Community ABSTRACTElectrical insulation is one of the most challenging issues governing the engineering exploitation of niobium-tin conductors. This is especially true for future accelerator magnets manufactured by the "wind-and-react" route. Applications such as the LHC Interaction Region upgrade or in the longer term an LHC energy upgrade will require magnets to operate at high fields in demanding thermal and radiation environments. The Next European Dipole (NED) programme is aimed at the development of a large aperture (up to 88mm) high field (up to 15T conductor peak field) superconducting dipole magnet relying on niobium-tin conductors. Conventional insulation development is being addressed in two key areas, the engineering requirements for large scale magnet manufacture and the improvement of materials properties for magnet operation and performance. The paper will review the status of insulation technology for niobium-tin accelerator magnets and define the special requirements for NED. Particular emphasis will be placed on the development of fibre sizing technology and its influence on magnet manufacture and electrical/mechanical performance of insulation laminates.

The Short Model Coil (SMC) assembly has been designed, as test bench for short racetrack coils wound with Nb 3 Sn cable. The mechanical structure comprises an iron yoke surrounded by a 20 mm thick aluminium alloy shell, and includes four loading pads that transmit the required pre-compression from the outer shell into the two coils. The outer shell is pre-tensioned with mechanical keys that are inserted with the help of pressurized bladders and two 30 mm diameter aluminium alloy rods provide the axial loading to the coil ends. The outer shell, the axial rods, and the coils are instrumented with strain gauges, which allow precise monitoring of the loading conditions during the assembly and at cryogenic temperature during the magnet test. Two SMC assemblies have been completed and cold tested in the frame of a European collaboration between CEA (FR), CERN and STFC (UK) and with the technical support from LBNL (US). This paper describes the main features of the SMC assembly, the experience from the dummy assemblies, the fabrication of the coils, and discusses the test results of the cold tests showing a peak field of 12.5 T at 1.9 K after training.

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Abstract-Thecable, by applying different levels of pre-stress. To fully satisfy this purpose, a versatile and easy-to-assemble structure has been realized. The design of the SMC magnet has been developed from an existing dipole magnet, the SD01, designed, built and tested at LBNL with support from CEA. The goal of the magnetic design presented in this paper is to match the high field region with the high stress region, located along the dipole straight section. For this purpose, three-dimensional nonlinear parametric models have been implemented using three codes (CAST3M, ANSYS, and OPERA). This optimization process has been an opportunity to cross-check the codes. The results of this benchmarking are presented here, along with the final design which incorporates the use of end spacers and a surrounding iron structure to deliver a nominal field of 13 T uniformly distributed along the cable straight section.

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