F. P. Juster

Iseult/INUMAC Whole Body 11.7 T MRI Magnet Status

A Whole Body 11.7 T MRI Magnet is presently being developed at the CEA Saclay for the Iseult/Inumac project, a French-German initiative focused on very-high-magnetic-field molecular imaging to improve sensitivity, spatial, temporal, and spectral resolution for preclinical and/or clinical MR systems. The magnet will be installed at the Neurospin center, Saclay, in 2012. This actively shielded magnet system, with a stored energy of 338 MJ and an inductance of 308 H, has external dimensions of 5 m in diameter and 5.2 m in length. The magnet will operate at a homogeneous field level of 11.75 T within a 90 cm warm bore and at a current of 1483 A. The technological choice for the cryostable winding is a double pancake structure, using NbTi conductors cooled with a pressurized bath of Helium II at 1.8 K. In April 2009, the project passed an important milestone with the publication of the Technical Design Report, which defines the engineering parameters, design of the magnet, and establishes its engineering feasibility. In the paper, the status of the 11.7 T magnet is reviewed and the future developments are presented.

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.

A New Design for the Superconducting Outsert of the GHMFL 42+ T Hybrid Magnet Project

A new superconducting coil outsert has been designed to be integrated within the existing infrastructure of the GHMFL hybrid project. Based on the novel development of a Nb-Ti Rutherford Cable On Conduit Conductor (RCOCC) cooled at 1.8 K by 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 bore diameter. Combined with resistive insert coils, an overall continuous magnetic field of 42+ T will be produced in a 34 mm warm aperture. The main results of the conceptual study are reported including the conductor and coil specifications, the mechanical stress analysis, the coil protection scheme as well as the required cryogenics infrastructure. First developments and tests regarding the RCOCC are also presented.

Quench Propagation in YBCO Pancake: Experimental and Computational Results

High-temperature superconductors are promising materials for future applications such as high field magnets thanks to their ability to carry high current densities. Nevertheless, their protection still remains a key issue mainly due to the slow velocity of quench propagation. To understand the quench behavior of a YBCO coil, a simulation code has been developed using the CASTEM-CEA finite element software. Simulations can be performed considering constant current and magnetic field. Results of those simulations will be displayed and a way for improving the protection by adding a stabilizer will be discussed. Two well instrumented YBCO coils were fabricated in order to obtain experimental data on quench propagation in pancake configuration. Their design and some measurements are reported in this paper along with another experiment on a double pancake made by and tested at CNRS Grenoble. Finally, we compare the numerical and experimental results and discuss the accuracy of our simulations.

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 ¿m) to enable the magnetic field homogeneity. Secondly, it must attain simultaneously a low electrical resistance (20 ¿¿/m at 10 K and 12 T) and a high mechanical strength (¿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.

Design and Test of a Small React‐and‐Wind MgB 2 Double Pancake

In the framework of the project on development of an integrated system for the production of PET tracers based on a dry NbTi supraconducting cyclotron called Lotus, the CEA and SigmaPhi examine the possibility of replacing the NbTi by MgB2. The aim of this work is to develop design tools and technologies for dry MgB2 magnet winding by the react-and-wind process. To validate this work, two dry prototype magnets have been developed: a solenoid of 1 T and a double pancake. To test these prototypes in conditions close to the Lotus cyclotron, a dry test facility, previously developed, will be used up to 3 T. This paper presents the double pancake design, fabrication, instrumentation, and the first test. The critical current and the n-value of the double pancake have been measured and compared with the sample measurement.

Iseult/INUMAC 11.7 T Conductor Production Status

The Iseult/INUMAC 11.7 T MRI magnet uses NbTi conductors larger than those typically used in conventional MRI magnets. The principal conductors are the main coil one, producing the magnetic field of 11.7 T and the conductor of the shielding coil that limits the fringe field. Both conductors are being produced by Luvata Waterbury Inc. The main coil conductor is a Rutherford cable in a copper channel (160 km) and carries 1500 A at 12 T and 2.8 K (2727 A at 9.5 T and 4.2 K). The shielding coil conductor is a wire in channel (60 km) and carries 2100 A at 5 T and 4.2 K. The conductor shape must be very precise with reproducible dimensions (tolerances below 15 microns) to enable good magnetic field homogeneity. They must also simultaneously exhibit a low electrical resistance (20 μΩ/m at 10 K and 12 T) and a high mechanical strength (σ0.2%>;250 MPa). Conductors of this industrial production are characterized by mechanical, electrical and geometrical measurements.

Magnetic Tests of the CMS Superconducting Magnet

The superconducting magnet for CMS has been designed to reach a 4 T field in a free bore of 6 m over a length of 12.5 m, with a stored energy of 2.6 GJ at nominal current. The magnet has been extensively and successfully tested in a surface hall at CERN in August and October 2006. Its characteristics make it the largest superconducting solenoid ever built in terms of bending power for the physics, stored energy and stored energy per unit of cold mass. The tests of the magnet were carried out by charging it to progressively higher currents. Long current flattops were used for magnetic measurements, generally ending with triggered fast discharges. During the tests, all the relevant parameters related to electrical, magnetic, thermal and mechanical behavior have been recorded and will be reported in the paper. Special emphasis will be put on the results and analysis of phenomena related to induced fast discharges, such as coupling and quench-back effects.

Stability and quench propagation velocities measurements on the 'racetrack' mock-up of ATLAS toroid coil

A mock-up of ATLAS toroid coil, which is one of the 3 detectors presently under construction for the future Large Hadron Collider at CERN, had been tested at Saclay. Various experiments have been led to check the validity of important technical options for the magnet. This paper focuses on thermal stability and quench propagation velocities measurements. For a 70/spl times/7 mm/sup 2/ aluminum-stabilized conductor carrying a 20 kA current, a 4-5 joule minimum quench energy and a 20 m/s longitudinal quench propagation velocity were found. We also studied the dependence of those features according to the operating current in the 5-20 kA range.

A New Test Facility to Characterize React and Wind

A new test facility was developed at CEA/Saclay in collaboration with the SigmaPhi Company in order to perform studies of a dry MgB2 magnet operating at 10 K and medium range field (1 T up to 4 T). For a rapid use of the MgB2 conductors in an industrial product, notably in the medical sector, the “react and wind” technique must be used to wind magnets. However, the reacted MgB2 conductors have a minimum winding radius, classically around 100 mm, which is incompatible with the existing Saclay test facility. A new test facility has been constructed with a 600 A dc current power, a 300 mm diameter sample holder, and conduction cooling by a two-stage GM cryocooler. The background field for this test facility is provided by a NbTi coil, which has a warm bore of 350 mm and a maximum field of 3 T. This paper presents the design of this test facility, especially the design of the current leads, the insulated thermal contacts with the development of a new type of insulation based on aluminum nitride and the dry sample holder. Results of critical current tests in self-field are presented and compared with manufacturer data for a reacted MgB2 conductor, a Ni/MgB2 tape soldered on an OFHC copper stabilizer tape, supplied by Columbus Superconductors SpA.