P. Bredy

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.

Status of the construction of the CMS magnet

CMS (compact muon solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The stored magnetic energy is 2.6 GJ. The magnet is being assembled in a surface hall and will be tested at the beginning of 2005 before being transferred to an experimental hall 90 m below ground level. The design and construction of the magnet is a common project of the CMS Collaboration. The task is organized by a CERN based group with strong technical and contractual participation of CEA Saclay, ETH Zurich, Fermilab, INFN Genova, ITEP Moscow, University of Wisconsin and CERN. The return yoke, 21 m long and 14 m in diameter, is equivalent to a thickness of 1.5 m of saturated iron interleaved with four muon stations. Manufacture of the yoke and vacuum tank is completed and the first sub-detectors have been installed. The indirectly-cooled, pure-aluminum-stabilized coil is made up from five modules internally wound with four layers of a 20 kA mechanically-reinforced conductor. The manufacture of the conductor is completed and winding is in progress for a final assembly in 2004. All ancillaries are delivered or under contract. The magnet project is described, with emphasis on the present status of the fabrication.

Final design of the CMS solenoid cold mass

The 4 T, 12.5 m long, 6 m bore diameter superconducting solenoid for the CMS (Compact Muon Solenoid) experiment at LHC will be the largest and the most powerful superconducting solenoid ever built. Part of the CMS design is based on that of previous large superconducting solenoids-the use of a high purity aluminium stabilized conductor, a compact impregnated winding with indirect cooling and quench back protection process. However, the dimensions and the performances of this solenoid have imposed solutions which are more than extrapolations of the previous ones : the use of a mechanically reinforced conductor and a five module winding, each module being made of four layers, internally wound. This design, which is now frozen, relies on numerous magnetic, mechanical and thermal calculations, on various experimental tests (characterization of structural and insulating materials, electrical joints...) and specific mock-ups. Two pre-industrialization programs, concerning the conductor and the winding process have also been carried out with industrial partners to support the foreseen solutions. Both the final design and the experimental results obtained to validate this design are presented in this paper.

Commissioning of the CMS Magnet

CMS (compact muon solenoid) is one of the large experiments for the LHC at CERN. The superconducting magnet for CMS has been designed to reach a 4 T field in a free bore of 6 m diameter and 12.5 m length with a stored energy of 2.6 GJ at full current. The flux is returned through a 10 000 t yoke comprising of five wheels and two end caps composed of three disks each. The magnet was designed to be assembled and tested in a surface hall, prior to be lowered at 90 m below ground, to its final position in the experimental cavern. The distinctive feature of the cold mass is the four-layer winding, made from a reinforced and stabilized NbTi conductor. The design and construction was carried out by CMS participating institutes through technical and contractual endeavors. Among them CEA Saclay, INFN Genova, ETH Zurich, Fermilab, ITEP Moscow, University of Wisconsin and CERN. The construction of the CMS Magnet, and of the coil in particular, has been completed last year. The magnet has just been powered to full field achieving electrical commissioning. After a brief reminder of the design and construction the first results of the commissioning are reported in this paper.

Tests of a Prototype for Assessing the Field Homogeneity of the Iseult/Inumac 11.7 T Whole Body MRI Magnet

A neuroscience research center with very high field MRI equipment was opened in November 2006 by the CEA life science division. One of the imaging systems requires a 11.75 T magnet with a 900 mm warm bore, the so-call Iseult/Inumac magnet. Regarding the large aperture and field strength, this magnet is a challenge as compared to the largest MRI systems ever built, and will be developed within an ambitious R&D program. With the objective of demonstrating the possibility of achieving field homogeneity better than 1 ppm using double pancake windings, a 24 double pancakes model coil, working at 1.5 T has been designed. This model magnet was manufactured by Alstom MSA and tested at CEA. It has been measured with a very high precision, in order to fully characterize the field homogeneity, and then to investigate and discriminate the parameters that influence the field map. This magnet has reached the bare magnet field homogeneity specification expected for Iseult and thus successfully demonstrated the feasibility of building a homogenous magnet with the double pancake winding technique.

CMS Solenoid Assembly

CMS (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with a 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The assembly of the solenoid on CERN site starts with the building up, the electrical and hydraulic connection of the 5 coil modules. After instrumentation cabling, the outer thermal shield is mounted. The cold mass is then swiveled and inserted inside the outer vacuum tank. The cold mass is supported from the outer vacuum tank by a set of titanium tie rods. After inserting the inner vacuum tank and its thermal shield, both end of the cryostat are closed. In parallel, the current leads and the cryogenic chimney are connected to the coil. This paper describes all these activities and in particular the checks performed at each step of the coil assembly

CMS coil design and assembly

The Compact Muon Solenoid (CMS) is one of the general-purpose detectors to be provided for the LHC project at CERN. The design field of the CMS superconducting magnet is 4 T, the magnet length is 12.5 m, and the free bore is 6 m. The construction phase of the superconducting coil is now in full progress. Due to the size and characteristics of the coil (4 T central field, 2.7 GJ stored energy), its design and the practical realization thereof require solutions which are more than extrapolations of those previously used for superconducting solenoids dedicated to physics experiments. This paper summarizes the coil design with a particular emphasis on the engineering aspects of its components, and their status. The developments that have been done to validate the solutions that are now finalized, will be reported. Finally, the assembly scenario of the coil, which will be mainly done in a vertical position before swiveling to a horizontal position, will be described.

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.

High Reliability and Availability of the Iseult/Inumac MRI Magnet Facility

A new innovative Whole Body 11.7-T MRI magnet is currently being manufactured at Alstom Belfort as part of the Iseult/Inumac project. It will be installed in 2016 in a neuroscience research center with other very-high-field MRI equipment, operating in France at CEA Saclay. The magnet has external dimensions of 5 m in diameter and 5 m in length, with a stored magnetic energy of 338 MJ. 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 in driven mode. The external cryoplant is connected to the magnet, and it provides pressurized Helium II at 1.8 K. The magnet facility has to operate 24 h a day continuously for several years. Therefore, all external components have been designed to avoid magnet discharge as much as possible in case of failure from the mains, power supplies, liquefier, helium compressor, etc. In order to increase its reliability, the quench detection system is based on majority voting redundancy. This paper describes the redundancy of the power supplies system, the architecture of the magnet safety system, the high availability of the magnet control system, and cryogenic supply.

High Field Insert Demonstrator Design, Manufacturing, and Tests of the Iseult Whole Body 11.75 T MRI Magnet

A neuroscience research center with very high field magnet resonance imaging (MRI) equipment has been opened in November 2006 in the Neurospin site of French Atomic Energy and Alternative Energies Commission (CEA, Saclay, France). One of the imaging systems, the so-called Iseult project, will require a whole body 11.75 T MRI magnet with a 900-mm warm bore. The coil is made of a niobium-titanium conductor cooled by a He II bath at 1.8 K, permanently connected to a cryoplant. The main coil is made of a stack of 170 double pancakes submitted to a peak field up to 12 T. A demonstrator made of six reduced double pancakes using the conductor developed for this project has been designed, manufactured, and tested at CEA/Saclay. The objective was to demonstrate that the Iseult main coil winding pack is able to sustain the high stress level calculated, 170 MPa azimuthally and 110 MPa radially. This demonstrator has been successfully energized up to 6000 A in a background field. A maximum azimuthal stress of 225 MPa has been reached, much higher than the nominal Iseult value. This paper presents the design, the manufacturing, and the cryogenics test results of this demonstrator.