C. Berriaud

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.

On-Surface Test of the ATLAS Barrel Toroid Coils: Overview

The Barrel Toroid (BT) provides the magnetic field for the muon detectors in the ATLAS experiment at CERN. The Toroid is built up from eight superconducting coils. Each coil consists of two 25 m times 5 m racetrack shape double pancakes impregnated and pre-stressed inside an aluminum coil casing. The 42-tons cold mass is cooled by forced-flow liquid helium circulating in aluminum pipes glued to its surface. The coils are tested on surface prior to their underground installation. The test program has started in September 2004 and finished in June 2005. This paper describes the test set up and various commissioning tests performed at the ATLAS Magnet Test Facility. It includes the aspects of test preparation, vacuum pumping, leak testing, cooling down, powering and warming up. The 8 coils have passed the tests successfully and have been assembled into the Toroid in the ATLAS cavern. The testing completes the production of the so far largest racetrack coils in the world

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.

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

Progress Report on the 43 T Hybrid Magnet of the LNCMI-Grenoble

A CEA-CNRS French collaboration is currently developing a new hybrid magnet to produce in a first step a continuous magnetic field of 43 T in a 34-mm warm bore aperture. This magnet combines a resistive insert, composed of Bitter and polyhelix coils, and a large bore superconducting “outsert.” The superconducting coil is based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by a bath of superfluid helium at atmospheric pressure. It aims at producing a nominal magnetic field of 8.5 T in a 1.1-m cold bore diameter. The specifications of the RCOCC will be presented together with the design and parameters of the cryogenic system. The solution to reduce the coupling between resistive and superconducting coils will be recalled as well as the constraints for designing the mechanical structure. The design study phase is coming to an end. The status of the conductor production and the next steps of the project are presented.

On-Surface Tests of the ATLAS Barrel Toroid Coils: Acceptance Criteria and Results

Each superconducting coil of the ATLAS Barrel Toroid has to pass the commissioning tests on surface before the installation in the underground cavern for the ATLAS Experiment at CERN. Particular acceptance criteria have been developed to characterize the individual coils during the on-surface testing. Based on these criteria and the limited time of the test, a compressed test program was proposed and realized. In only a few cases some additional tests were required to justify the coil performance and acceptance. In this paper the analysis of the test results is presented and discussed with respect to the acceptance criteria. Some differences in the parameters found between the identical coils are analyzed in relation to coil production features

Theoretical and Experimental Investigation of the Ramp Losses in Conductor and Coil Casing of the ATLAS Barrel Toroid Coils

Each of the eight huge coils of the Barrel Toroid of the ATLAS detector consists of two double pancakes which are embedded in an aluminum alloy coil casing. The 57 mm times 12 mm sized conductor is a Rutherford cable with NbTi-Cu strands co-extruded with a high purity aluminum stabilizer. The race track coils have overall dimensions of 25 m times 5 m and the length of the conductor in the windings is 6.7 km. The coils are conduction cooled with forced flow helium. The nominal operating current is 20.5 kA and the nominal ramp rate is 4 A/s. During the test program of the individual coils the ramp losses are measured to confirm that they do not exceed the design cooling capacity of the ATLAS cryogenic system. The losses are determined from the amount of evaporated helium in the return flow. The ramp losses in the conductor consist of the hysteresis and coupling current losses in the Rutherford cable and eddy current loss in the pure aluminum stabilizer. Ohmic losses are generated in the coil casing which acts as a low resistive secondary of a transformer formed by the coil and the casing. In this paper the results of the loss measurements on the different coils, with different RRR (residual resistance ratio), are presented. Measurements are performed at various ramp rates. The results are in good agreement with the calculated losses, which are dominated by the loss in the coil casing

Completion of the Manufacturing of the ATLAS Barrel Toroid Magnet at CERN

The last two years have seen the completion of the integration and the cryostating of 8 superconducting coil windings for the ATLAS Barrel Toroid air-core magnet (BT). The Barrel Toroid is a 20 m in diameter, 25 m long and 5 m wide superconducting magnet for ATLAS, one of the two experiments dedicated to the search of the Higgs boson, which will be installed on the LHC ring at CERN in 2006. The paper presents the last steps of this integration progress which ends with the cold acceptance tests. A special emphasis is put on the integration of the cold mass into the vacuum vessel. The integration of the windings in their coil casings has been completed in October 2003 and the last coil cryostating was performed in June 2005. The BT coils are now being installed in the ATLAS cavern at CERN