C. Mayri

The Iseult/Inumac Whole Body 11.7 T MRI Magnet R&D Program

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 when compared to the largest MRI systems ever built, it is being developed within an ambitious R&D program, Iseult, focused on high field MRI. The conservative MRI magnet design principles are not readily applicable, 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 order to develop the magnet design on an experimental basis, an ambitious R&D program has been set-up based on magnet prototypes, high field test facility (Seht) and stability experiments. The main results from these experiments and their impact on the Iseult magnet design will be discussed.

HTS Dipole Insert Developments

Future accelerator magnets will need to reach a magnetic field in the 20 T range. Reaching such a magnetic field is a challenge only reachable using high temperature superconductor (HTS) material. The high current densities and stress levels needed to satisfy the design criterion of such magnets make YBaCuO superconductor the most appropriate candidate especially when produced using the IBAD route. The HFM EUCARD program is aimed at designing and manufacturing a dipole insert made of HTS material generating 6 T inside a Nb3Sn dipole of 13 T at 4.2 K. In the HTS insert, engineering current densities higher than 250 MA/m2 under 19 T are required to reach the performances. The stress level is consequently very high. The insert protection is also a critical issue as HTS shows low quench propagation velocity. The coupling with the Nb3Sn dipole makes the problem even more difficult. The magnetic and mechanical designs of the HTS insert will be presented as well as the technological developments underway to realize this compact dipole insert.

Study and Development of the Superconducting Conductor for the Grenoble Hybrid Magnet

To produce a continuous magnetic field of at least 8.5 T in a 1.1 m cold bore diameter, the superconducting outsert of the Grenoble Hybrid magnet is based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled to 1.8 K by a bath of superfluid helium pressurized at atmospheric pressure. The main results of the conductor studies and development are presented after a brief introduction to the specificity of hybrid magnets, namely the electromagnetic couplings between resistive and superconducting coils. Results obtained with short samples of conductor are reviewed including the measurements of the elastic limit, AC losses, stability and critical current. The final specification of the RCOCC is presented highlighting the proposed method for the industrialization of the insertion process of the Rutherford cable on the hollow Cu-Ag stabilizer as well as its validation phase on short samples.

Manufacturing and integration progress of the ATLAS barrel toroid magnet at CERN

ATLAS is one of the two experiments dedicated the search of the Higgs boson, which will be installed on the LHC ring at CERN in 2006. The ATLAS barrel toroid air-core magnet (BT) is 20 m in diameter and consists of 8 superconducting coils, each one 25 m long and 5 m wide. After several years of technological development, the major concepts have been proved in 1999/2000 during the construction of the B0 prototype; a technological model for BT. The delivery by several European industrial companies of all the major components for BT is nearly finished. The eight BT coils are now being integrated at CERN. The paper presents a general overview of the component manufacturing and integration progress. A special emphasis is put on the major component delivery (conductor, double pancake windings, aluminum coil casing and cryostat) together with a description of the two phases of the integration process: integration of the windings into their coil casings and integration of the cold mass into the vacuum vessel. The integration of the windings in their coil casings will be completed in October 2003. The closure of the first cryostat is planned for the end of the year. The start of the first cold test and the assembly in the cavern is foreseen for the beginning of 2004.

Design Status of the R3B-GLAD Magnet: Large Acceptance Superconducting Dipole With Active Shielding, Graded Coils, Large Forces and Indirect Cooling by Thermosiphon

The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering design is undertaken. One main feature of this butterfly-like magnet with graded, tilted and trapezoidal racetrack coils is the active shielding. It makes it possible to decreasing the field by two orders of magnitude within a 1.2 m length, despite the large opening on the outlet side of the magnet (around 0.8 square meters). The fringe field is lower than 20 mT in the target area beside the entry, while the main field is larger than 2 teslas, out of 2 m length. The other principal characteristics are as follows: first, a high level of magnetic forces (300 to 400 tons per meter), with little place to block the coils, requiring a very specific mechanical structure; then, the magnet protection system that is based on an external dump resistor, coupled to a strong quenchback effect, to prevent any damage of the coils which could be caused by the 24 MJ of stored energy; lastly, the indirect cooling of the cold mass with a two-phase helium thermosiphon. The overall size of the conical cryostat will be around 3.5 m long, 3.8 m high and 7 m broad.

Assembly Concept and Technology of the ATLAS Barrel Toroid

The ATLAS detector for the LHC collider at CERN requires a large superconducting Barrel Toroid (BT) with overall dimensions of 25 m length, 22 m diameter which is installed in the ATLAS cavern 100 m underground. The Barrel Toroid provides the magnetic field for the muon detector. The toroid is assembled from 8 flat race track coils of dimensions 25 m times 5 m. Following the on-surface acceptance test of the 8 BT coils, they are successively inserted in the underground cavern and assembled as a full toroid by using 16 supporting rings of struts that link the 8 coils to form a rigid and stable structure. The total mass of the toroid is 850 t. Particular issues are that the axis of the toroid has to be horizontal and the final shape of the toroid cylindrical with a tolerance of +/-10 mm with respect to an overall system diameter of 22 m. The desired shape of the toroid can only be controlled by installing the 8 coils in calculated positions in space (forming an elliptic shaped structure), and by linking them using bolted struts linking the coils. The final release of the structure is done under its self weight hydraulically. This required very large tooling essentially to support all the 8 coils in space in a nearly stress free condition until the toroid supporting rings have been closed. The theoretical positions are found by performing detailed 3-D Finite Element Calculations that predict the shape of the toroid under its operational load. The assembly of this huge toroid is unique and no experience basis exists. This paper presents the concept and technology required for the assembly of the toroid as well as the cryogenic supply lines, highlights the FEA mechanical calculations performed to predict the shape, summarizes the tooling required and reviews the experience gained during the installation

Cold Mass Integration of the ATLAS Barrel Toroid Magnets at CERN

The ATLAS Barrel Toroid, part of the ATLAS Detector built at CERN, is comprised of 8 coils symmetrically placed around the LHC beam axis. The coil dimensions are 25 m length, 5 m width and 0.4 m thickness. Each coil cold mass consists of 2 double pancakes of aluminum stabilized NbTi conductor held in an aluminum alloy casing. Because the magnet is conduction cooled a good bonding between the superconducting winding and the coil casing is a basic requirement. Due to the high load level induced by the Lorentz forces on the double pancakes, a pre-stressing technique has been developed for the assembling of the double pancake windings in the coil casing. This prestressing technique uses inflatable bladders made of extruded aluminum tubes filled with glass microballs and epoxy resin then cured under pressure. The paper describes the design of the system as well as the problems occurred during the assembling of the 8 superconducting ATLAS coils and the ATLAS B0 prototype coil, and the behavior of the Barrel Toroid coils with respect to this prestress during the cold tests

Suspension System of the Barrel Toroid Cold Mass

The ATLAS Barrel Toroid consists of 8 racetrack coils symmetrically placed around the LHC beam axis. The coil dimensions are 25-m of length, 5-m of width and 1-m of thickness. Each cold mass is held in its cryostat by different types of supports. The paper describes the design, the tests and the behavior of each element during on surface test of individual coils

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.

Progress in Design and Construction of the

The R3B-Glad superconducting Magnet is a large acceptance dipole, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. It takes part in the FAIR Project at GSI. As the superconducting NbTi Rutherford cable was under production, detailed studies of the mechanical structure (with both simulation and experiment on a half-scale mock-up) led to revise the magnet design and to abandon the grading of the coils in three stages. Due to the large magnetic forces (up to 400 tons/m), the maximum shear stress level of 20 MPa was impossible to meet in the coils. The main reasons consist in the orthotropic thermo-mechanical behavior of the coils together with the large differential thermal shrinkage between the Cu stabilized coils and their Al alloy casings. Indeed after several studies of different mechanical designs, we decided to simplify the magnet in order to cope with these difficulties. One innovative point is that the coils are not blocked at room temperature, but only at 4.5 K. This paper presents the magnetic calculations of this active shielded magnet, and shows how the new design features meet the specifications. Currently, the 22 tons magnet cold mass, i.e. the 6 coils and their integration in the casings, is ordered and under construction. Meanwhile, the design of the magnet cryostat has evolved into a shape of elliptical cylinder with a lateral satellite. The total weight is expected to be around 50 tons.