Objective To assess the possible influence of third-order shim coils on the behavior of the gradient field and in gradient–magnet interactions at 7 T and above. Materials and methods Gradient impulse response function measurements were performed at 5 sites spanning field strengths from 7 to 11.7 T, all of them sharing the same exact whole-body gradient coil design. Mechanical fixation and boundary conditions of the gradient coil were altered in several ways at one site to study the impact of mechanical coupling with the magnet on the field perturbations. Vibrations, power deposition in the He bath, and field dynamics were characterized at 11.7 T with the third-order shim coils connected and disconnected inside the Faraday cage. Results For the same whole-body gradient coil design, all measurements differed greatly based on the third-order shim coil configuration (connected or not). Vibrations and gradient transfer function peaks could be affected by a factor of 2 or more, depending on the resonances. Disconnecting the third-order shim coils at 11.7 T also suppressed almost completely power deposition peaks at some frequencies. Discussion Third-order shim coil configurations can have major impact in gradient–magnet interactions with consequences on potential hardware damage, magnet heating, and image quality going beyond EPI acquisitions.

The whole-body Iseult 11.7T CEA magnet has delivered its first images after nearly 20 years of research and development. Before reaching this long-waited step, a gradient coil–magnet interaction test campaign was run for several months at 3T, 7T, 10.2T and 11.7T on the same identical system. It included acoustics, vibrations, magnet safety system voltage and power deposition in the He bath measurements. Some vibration results versus field strength are presented here. Vibration amplitudes are shown to increase less than with B0 field strength.

The Iseult project started in 2001 and is a collaborative effort involving CEA and the University of Freiburg in academics, Guerbet, Siemens Healthineers and Bruker Biospin as industrial partners. One central aspect of the project has been the design by CEA of a whole-body magnet of 11.7T field strength with a 90-cm wide bore. After nearly 20 years of research and development, prototyping, integration and tests, first images have been acquired with this unique MRI scanner. Some key validation results are presented here.

The Iseult project is a French-German initiative focused on very high magnetic-field molecular imaging. The project includes a Whole Body 11.7 T MRI magnet installed at Neurospin, a neuroscience research center operating at CEA Saclay since November 2006. After 7 years of fabrication at Belfort by GE Power (Ex Alstom), the Iseult magnet was delivered to CEA in June 2017, its connection with the cryoplant and all the ancillary equipment was completed in October 2018. After 4 months of cooldown and another 4 months of tests, the Iseult magnet reached its nominal field of 11.72 T without any quench for the first time, on July 18th. This paper deals with the magnet connection at Neurospin with the cryoplant and with the electrical and control systems. Finally, the paper will present the magnet commissioning data, from the cooling phase to the step-by-step energization up to the nominal current.

We present results of calculations of the ultimate forces for the worst-case scenario, an important safety concern in hybrid magnets. They appear during a simultaneous and immediate burnout of some or all upper or lower resistive coil halves, or shorts between the coils in the mid-plain. Because of their intensity, they have a dramatic impact on the mechanical layout of a hybrid magnet. An electromagnetic shield between insert and outsert, as it is the case for the Grenoble hybrid magnet, takes up part of these forces and reduces them considerably. It makes the calculation of the now time dependent forces rather complex. The ultimate forces have been calculated for two models: a) conservation of magnetic flux with instantaneous energy transfer from the shorted coils to the remaining parts, and b) conservation of energy of the whole hybrid system, including the power supplies, with energy transfer via mutual axial and radial coupling to the other coils. Only for case a) we find an instantaneous force of 6 MN between resistive magnet and its housing at t = 0. The maximum force between resistive magnet and shield appears, when the resistive power supply is switched off at t = 50/100 ms: it is 3.7 MN/4.4 MN for case a) against only 1.5 MN for b). The force on the superconducting magnet is reduced from 210 kN for a) to 130 kN for b). The results underline the usefulness of a shield between insert and outsert to reduce their electrodynamic interaction. They also confirm that the Grenoble hybrid magnet is well suited for inserts of much higher power levels. Our findings have also consequences for the layout of hybrid magnets without shield.

A new innovative whole body 11.7 T MRI magnet is currently being manufactured at Belfort as part of the Iseult/Inumac project, a French-German initiative focused on very high magnetic-field molecular imaging. It will be installed in a neuroscience research center with other very high field MRI equipment, operating in France at CEA Saclay since November 2006. This actively shielded magnet system, m...

A new innovative whole-body 11.7-T MRI magnet is currently being manufactured at Alstom Belfort as part of the Iseult/Inumac project. The magnet will be installed by the end of the year in a neuroscience research center with other very high-field MRI equipment operating in France at CEA Saclay since November 2006. This actively shielded magnet system, which was manufactured from a NbTi superconductor, will generate a homogeneous magnetic field of 11.75 T within a 90-cm warm bore. This paper presents the geometrical controls performed on the Iseult/Inumac magnet during the different fabrication stages, and it compares them to the specifications. A FEM analysis taking into account magnet cooling down and energizing has also been performed, in order to estimate the final magnet homogeneity, taking into account load tests and geometrical measurement performed on the main coil. Measured field maps will be analyzed and compared to the field computation based on geometrical measurements.

In the new 43-T LNCMI hybrid magnet, a good conducting shield is inserted between the resistive insert magnet and the superconducting outsert magnet. Its goal is to decrease the ac losses induced in the superconducting conductor during a fault of the insert, disruption of the resistive coils (i.e., fast discharge) by smoothing the flux variations, and avoidance of a quench of the superconducting coil. The induced currents within the shield are very large due to the presence of copper material, which is the drawback of a good screening effect. Such currents result in large Lorentz forces, particularly during the most severe fault scenario of the resistive insert with the burnout of half of the Bitter coils. Finally, the detection system must be specially designed to handle the effects of the shield on the induced voltages.

Standard Magnetic Resonance magnets produce a single homogeneous field volume, where the analysis is performed. Nonetheless, several modern applications could benefit from the generation of multiple homogeneous field volumes along the axis and inside the bore of the magnet. In this communication, we propose a straightforward method using a combination of ring structures of permanent magnets in order to cancel the gradient of the stray field in a series of distinct volumes. These concepts were demonstrated numerically on an experimentally measured magnetic field profile. We discuss advantages and limitations of our method and present the key steps required for an experimental validation.

The end design is a critical step in the design of superconducting accelerator magnets. First, the strain energy of the conductors must be minimized, which can be achieved using differential geometry. The end design also requires an optimization of the magnetic field homogeneity. A mechanical and magnetic model for the conductors, using developable strips, is described in this paper. This model can be applied to superconducting Rutherford cables, and it is particularly suitable for High Temperature Superconducting tapes. The great advantage of this approach is analytic simplifications in the field computation, allowing for very fast and accurate computations, which save a considerable computational time during the optimization process. Some 3D designs for dipoles are finally proposed, and it is shown that the harmonic integrals can be easily optimized using this model.

A Nuclear Magnetic Resonance (NMR) instrument providing a rotating field oriented at the magic angle with the rotation axis has the potential to record high resolution NMR spectra from static heterogeneous samples exhibiting susceptibility broadening. The requirement of a high uniformity field and the possible need of imaging gradients induces several challenges in terms of shim and gradient generation. We discuss here key theoretical aspects in this context.

A novel one-sided NMR magnet has been validated for accurate measurements of diffusion in thin samples. Results are presented from the measurement of self-diffusion in several solvents, including the room temperature ionic liquid 1-butyl-3-methyl imidazolium bis(trifluoromethane)sulfonimide (BMIM-TFSI). We also present results from diffusion measurements of BMIM-TFSI confined in nanoporous anodized aluminum oxide (AAO) membranes (thickness 100 mu m), a promising electrolyte/membrane combination for portable energy devices. A reduction in the diffusion coefficient, compared to the bulk, has been observed in BMIM-TFSI confined in narrow pores (55 nm). The possible application of this instrument to in situ measurements of portable energy devices is discussed. (C) 2013 Elsevier Inc. All rights reserved.

In particle accelerators, the bending magnets have to be wound with flared ends. This particular shape induces an inhomogeneity in the magnetic field in the ends, which degrades the particle beam stability. This paper proposes a 3D modeling for conductors with rectangular cross-sections. The coil is first divided into blocks (parallelepipeds and arcs). Then the magnetic field is evaluated in every point of space by means of analytical formulas which allow an accurate computation. This method is also faster than numerical integrations of Biot and Savart law. Some optimization examples are finally presented and show that it is possible to minimize, with a few degrees of freedom only, the first field harmonics, integrated along the beam tube.

We present a thorough analysis of eddy currents that develop in a rectangular cross section toroid rotating in a uniform magnetic field. The slow rotation regime is assumed. Compact expressions for the current density, the total dissipated power, and the braking torque are given. Examination of the topology of current lines reveals that depending upon the relative dimensions of the side and length of the toroid two different regimes exist. The conditions of existence of the two regimes are analytically established. In view of nuclear magnetic resonance (NMR) applications, we derive the angular variation of the magnetic field created by eddy currents and lay down the formalism necessary for calculating the effect of this field on the NMR spectra of the conductor itself or of a sample co-rotating with the conductor, a situation encountered when dealing with rotating detectors. Examples of calculations for cases of practical interest are presented. The theory is confronted with available data, and we give guidelines for the design of optimized rotating micro-coils.

Mapping (or plotting) the magnetic field has a critical importance for the achievement of the homogeneous magnetic field necessary to standard MR experiments. A powerful tool for this purpose is the Spherical Harmonic Expansion (SHE), which provides a simple way to describe the spatial variations of a field in free space. Well-controlled non-zero spatial variations of the field are critical to MRI. The resolution of the image is directly related to the strength of the gradient used to encode space. As a result, it is desirable to have strong variations of the field. In that case, the SHE cannot be used as is, because the field modulus variations are affected by the variations of all components of the field. In this paper, we propose a method based on the SHE to characterize such variations, theoretically and experimentally, in the limit of an axisymmetric magnetic field. Practical applications of this method are proposed through the examples of single-sided magnet design and characterization, along with Stray-Field Imaging (STRAFI).

In this paper, we discuss the application of a systematic approach to magnet design to single‐sided magnets [1]. This approach, based on analytical expressions of the spherical harmonic expansion terms for basic magnet blocks allows to compute exact geometry parameters for structures optimized in homogeneity and field strength for a given amount of material. The case of homogeneous fields and a controlled strong gradients are treated separately. This method can be applied to both in situ and ex situ configurations. We present a possible single‐sided structure generating a strong gradient at a remote distance. This structure adopt an axial symmetry and is magnetized along its axis, generating a field along that axis. A prototype of this model has been fabricated and we report its initial performances. This magnet has been integrated with an optimized planar coil for single‐sided excitation and detection. Initial images of thin olive oil layers are also presented.

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.