Rolf Pfister

Final Design of the New Grenoble Hybrid Magnet

A CEA-CNRS French collaboration is currently developing a new hybrid magnet; this magnet combines a resistive insert composed of Bitter and polyhelix coils and a new large bore superconductor outsert to create an overall continuous magnetic field of 42+ T in a 34 mm warm aperture. The design of the superconducting coil outsert has been completed after thorough studies and successful experimental validation phases. Based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by the mean of a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m cold bore diameter. The main results of the final design studies of the superconducting coil are presented including the 2D and 3D mechanical stress analysis, the conductor and coil specifications, the coil protection system as well as the required cryogenics infrastructure. The final design of the resistive insert coils is also described.

Design Study of High Field Resistive Magnets for Diffraction Experiments

The European Synchrotron Radiation Facility (ESRF), and the Institut Laue Langevin neutron facility (ILL) in collaboration with the Laboratoire National des Champs Magne¿tiques Intenses (LNCMI-CNRS) have performed during 2008 a design study for the implementation of continuous high magnetic fields suitable for diffraction studies. Two main designs have been studied: a horizontal field magnet suitable for back scattering and absorption experiments and a split magnet.

A new test station to measure the critical current of superconducting strands

A test station for critical current measurements of superconducting strands with lengths up to 1.6 m has been developed at LNCMI-Grenoble. A modular cryostat has been designed for its integration within the existing infrastructures of the laboratory including the 24 MW sites of resistive magnets for continuous magnetic fields up to 35 T. The sample holder can carry up to 10 strands wound in coils of 44 mm diameter and stacked up around a common current lead, which allows using the expensive magnet time more efficiently. To reduce the thermal load, a novel integrated switching unit containing 10 high current contactors operating in liquid helium has been implemented in order to connect alternately the remaining terminal of each strand sample to the second current lead. First results of critical current measurement obtained in a 10 T superconducting solenoid are presented. They allow the determination of the sensitivity and precision of this set-up. Finally, solutions to further improve this station are discussed .

Cryogenic system for the 43 T Hybrid Magnet at LNCMI Grenoble: from the needs to the commissioning

LNCMI is one of the unique worldwide laboratories offering the scientific community access to various experimental conditions with continuous magnetic fields well above 20 T. LNCMI is currently developing a large field flexible experimental platform. One configuration will produce a continuous magnetic field of 43 T in a 34 mm warm bore aperture from the combination of homemade resistive electromagnet inserts and a large bore outer superconducting magnet (1.1 m internal cold dia.), the latter being built in close collaboration with CEA-IRFU Saclay. The superconducting magnet with its mechanical structure and its helium vessel will represent a mass of 22 tons to cool down to 1.8 K and maintain at this temperature 10 months per year. An overview of the project will be given focusing on the cryogenics and particularly on the helium liquefier designed and manufactured by Air Liquide Advanced Technologies. This system - the most powerful even produced in the Helial ML range - and its ancillaries has been integrated and commissioned as a turnkey system in the existing site of LNCMI.

Two-Dimensional and Three-Dimensional Mechanical Analyses of the Superconducting Outsert of the LNCMI Hybrid Magnet

Current technical superconductors, such as Nb3Sn, are limited to fields around 20 T by their intrinsic material properties. Generating significantly stronger magnetic fields can only be done by using resistive magnets, or by combining superconducting and resistive magnets (hybrid magnets), at the expense of large power consumption and operating cost. A CEA-CNRS French collaboration is currently developing a new hybrid magnet, which combines a resistive insert composed of Bitter and polyhelix coils and a new large-bore superconductor outsert to produce an overall continuous magnetic field of more than 42 T in a 34-mm warm aperture. Based on the novel development of a NbTi/Rutherford cable on conduit (RCOCC) cooled down to 1.8 K by means of the bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1-m cold bore diameter. This paper summarizes the results of the mechanical behavior study of the cold mass cooled from room to operating temperature and Lorentz forces at operating temperature. Computations have been performed in 2-D axisymmetry and 3-D, to take into account the axisymmetric discontinuous distribution of the tie rods.

Status of the 43-T Hybrid Magnet of LNCMI-Grenoble

Based on a close collaboration between CEA and CNRS, a new hybrid magnet is being built at LNCMI-Grenoble. By combining a resistive insert, which is made of Bitter and polyhelix coils, with a large bore superconducting outsert, an overall continuous magnetic field of at least 43 T will be produced in a 34-mm warm bore aperture. The superconducting coil relies on the novel development of a Nb-Ti/Cu Rutherford cable-on-conduit conductor cooled down to 1.8 K by a bath of superfluid helium at atmospheric pressure and will produce a nominal magnetic field of 8.5 T in a 1.1-m cold bore diameter. After thorough reviews of the hybrid magnet design, which have anticipated possible upgrades of the maximum magnetic field produced, the project has entered in its production phase. The status and the next steps of the project will be reviewed highlighting the remaining technical challenges.