Neurospin is a neuroscience research center located in France at the Atomic Energy Commission (CEA Saclay). The facility is hosting an innovative whole-body 11.7 T MRI system that has delivered its first images in October 2021. The core part of the Iseult MRI is an actively shielded NbTi magnet cooled with a pressurized superfluid helium bath at 0.125 MPa and 1.8 K, providing a homogeneous magnetic field of 11.7 T within a 90 cm warm bore. After nearly twenty years of work and efforts, the magnet successfully reached its nominal field for the first time in July 2019. The field homogeneity has been adjusted and the control system tested against internal and external faults that could affect the future MRI operation. MRI peripheral equipment has been integrated and interactions between the gradient coils and the magnet and their impact on cryogenics and on the magnet safety system have also been studied. The MR scanner is now kept permanently at nominal field and the final calibration is on-going to prepare the first acquisition on a human volunteer. The paper will present the Iseult MRI commissioning status and the first images obtained, as well as a first feedback on the cryogenic plant operation after three years and a half at 1.8 K.

The Iseult whole-body MRI delivered its first images in October 2021. The masterpiece of this MRI is an actively shielded NbTi magnet providing a homogeneous magnetic field of 11.7 T within a 90 cm warm bore. A dedicated cryoplant was constructed to cool the magnet at 1.8 K using a superfluid helium bath and it is in nominal operation since March 2019. This paper will present the cryoplant design, as well as the connection of the cryogenic ancillary equipment with the magnet. Estimated thermal losses will be compared with experimental data collected since the beginning of the cooling phase. Then, we will describe the system maintenance and the periodic controls of the various pressurized components performed keeping the continuous nominal operation of the MRI. Finally, we will present the first lessons learned on this unique cryogenic system operation and possible options to improve its reliability.

A new innovative whole-body 11.7-T MRI magnet is currently being manufactured at Alstom Belfort as part the Iseult/Inumac project, a French-German initiative focused on very high magnetic field molecular imaging. It will be installed at the end of year 2016 in a neuroscience research center with other very high field MRI equipment, operating in France at CEA Saclay since November 2006. The main coil constructed from a stack of 170 double pancakes of 2-m diameter, with a finished height of 4 m and 50 t in weight, has been completed within required tolerances. The two shielding coils, vacuum impregnated solenoids of 4 m in diameter and 10 t in weight, have been also completed within tolerances. A crack has been discovered inside the 2-m diameter mandrel of the cryogenic correction coils. A new mandrel has been manufactured, with delivery in July 2015. The main coil and the shielding coils have been integrated inside the helium vessel, and the assembly of thermal shield and vacuum vessel is due to start, with completion expected by the middle of 2016. The magnet will be serviced by a separate cryogenic and electrical facility; the installation of this external equipment will be completed by the end of 2015 when the first phase of the commissioning will start. Full tests and commissioning of the magnet at 1.8 K are expected at NeuroSpin at the beginning of 2017.

The Iseult system is a highly homogeneous 11.7 T superconducting magnet. This high field 900 mm warm bore coil will provide the main field of the Iseult/Inumac MRI system, dedicated to the Neurospin center of the CEA life science division. The cold mass structure of the magnet is designed to support and accurately locate the central and shielding coils. The main winding is made of a 3.8 m length stacking of 2 m outer diameter double-pancakes. Under self load, the axial compression of the main coil reaches 8100 t. The two shielding coils are 4 m outer diameter short length solenoids. The cold mass assembly consists of the main coil suspension and preload system, surrounded by the shielding coils casing. It weighs 105 t with envelop dimensions of 4 m diameter × 4 m length. The engineering design of the cryostat has been carried out. This paper gives a description of the system, and an overview of the mechanical behavior of the cold mass assembly.

A neuroscience research center with very high field MRI equipments has been opened in November 2006 by the CEA life science division. One of the imaging systems will require a 11.75 T magnet with a 900 mm warm bore. Regarding the large aperture and field strength, this magnet is a real challenge as compared to the largest MRI systems ever built, and is then developed within an ambitious R&D program, Iseult, focus on high field MRI. The conservative MRI magnet design principles are not readily applicable and other concepts taken from high energy physics or fusion experiments, namely the Tore Supra tokamak magnet system, will be used. The coil will thus be made of a niobium-titanium conductor cooled by a He II bath at 1.8 K, permanently connected to a cryoplant. Due to the high level of stored energy, about 340 MJ, and a relatively high nominal current, about 1500 A, the magnet will be operated in a non-persistent mode with a conveniently stabilized power supply. In order to take advantage of superfluid helium properties and regarding the high electromagnetic stresses on the conductors, the winding will be made of wetted double pancakes meeting the Stekly criterion for cryostability. The magnet will be actively shielded to fulfill the specifications regarding the stray field.

In the framework of the cryogenic cooling system design of the 4T CMS magnet, heat and mass transfer has been experimentally studied at CEA-Saclay on a 9-m high helium two-phase convection loop under atmospheric pressure. The loop includes a 5-m high heated section surmounted by a 4.5-m high collector and is connected to the final CMS phase separator. The heated section of the loop is composed of seven aluminum tubes placed in parallel and heated on one side to reproduce the heating configuration of the magnet cooling system. We focused in this paper on the hydraulic characteristics of the two-phase convection loop. Evolutions of mass flow rate and vapor quality are presented and analyzed as a function of the heat flux with an equations system based on the homogeneous model.

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.

We studied heat transfer between copper tube and two-phase helium for different flow patterns. We can reach stratified wavy, intermittent and dispersed flow. The copper cell have two temperature sensors placed on top and bottom of the tube. For all flow regimes the upper and lower sensors record different heating in spite of the copper high thermal conductivity. The temperature ratio between upper and lower sensors can be up to 20. This difference vanishes for dispersed flow. Moreover, for both intermittent and stratified wavy flow, the boiling crisis occurs for heat flux of about 2 000 Wm−2 and for the whole section. As expected no boiling crisis appears for dispersed flow.

Two experimental apparatus have been built in our laboratory to study He I Two Phase Flow at atmospheric pressure. The first apparatus has been designed to create horizontal flows in a 0.01 m diameter tube. A 0.1 m long visualization has been realised to study flow patterns. Two types of heat transfer coefficient measurement cells have been developed (copper or stainless steel). Some typical results are shown. The second apparatus (under test) is designed to realise vertical flows in 0.01 to 0.014 m diameter tube. For flow patterns study, visualization is possible up to 0.9 m on a upward flow.