Superconducting Magnet

Rare Earth based coated conductors are very promising conductors for the construction of high field solenoids. Development of coil winding technique was started at the Tsukuba Magnet Laboratory: coils of various sizes (from 18 mm to 220 mm of an inner diameter) have been fabricated by layer-winding without impregnation in order to test the mechanical and superconducting properties. In the thin 220 mm diameter coil the Hoop stress reached over 500 MPa at 130 A in 14 T background field, without degradation of the superconducting properties. In the small diameter coils (18 mm of inner diameter) the tape was insulated using enamel to minimize the cross section and to enhance the coil current density. The highest field generated was 2.1 T in a background field of 18 T (total field was 20.1 T) at 4.2 K and the coil current density was 240 A/mm 2 .

High temperature superconductors such as MgB2 focus on conduction cooling of electromagnets that eliminates the use of liquid helium. With the recent advances in the strain sustainability of MgB2, a full body 1.5 T conduction cooled magnetic resonance imaging (MRI) magnet shows promise. In this article, a 36 filament MgB2 superconducting wire is considered for a 1.5 T full-body MRI system and is analyzed in terms of strain development. In order to facilitate analysis, this composite wire is homogenized and the orthotropic wire material properties are employed to solve for strain development using a 2D-axisymmetric finite element analysis (FEA) model of the entire set of MRI magnet. The entire multiscale multiphysics analysis is considered from the wire to the magnet bundles addressing winding, cooling and electromagnetic excitation. The FEA solution is verified with proven analytical equations and acceptable agreement is reported. The results show a maximum mechanical strain development of 0.06% that is within the failure criteria of −0.6% to 0.4% (−0.3% to 0.2% for design) for the 36 filament MgB2 wire. Therefore, the study indicates the safe operation of the conduction cooled MgB2 based MRI magnet as far as strain development is concerned.

Využitie MRI zariadení pre účely úschovy elektrickej energie It is well known, that the electrical energy storage in the large scale is basically a difficult process. Such a process is connected with energy losses, as most frequently it is the conversion of electrical energy into another form, for example mechanical, and then back to the primal electrical form. Though, the SMES technology offers the energy storage in an unchanged form, which is advantageous primarily in the achieved efficiency. The magnetic resonance imaging (MRI) devices, commonly used in the medical facilities are based on the basis of superconducting magnet. After its rejection from operation, (basically caused only by its "software fustiness" and not by functional faults), there is a possibility of using such devices for the energy storage purposes. Additionally, such a technology of storage is also ecological. A research project is running at the Faculty of Mining, Ecology, Process Control and Geotech...

Wendelstein 7-X (W7-X) is a fully optimized low-shear stellarator and shall demonstrate the reactor potential of this fusion plant. It is presently under construction at the Greifswald Branch Institute of IPP. The superconducting magnet system will allow continuous operation, limited only by the plasma exhaust system whose capacity is designed for 30 min full power operation. The Wendelstein 7-X (W7-X) coils and structures are part of the largest superconducting fusion device being constructed at present. They represent a technical challenge at industrial level and the need for proven techniques and manufacturing processes in accordance to the highest quality standards. The production of these components requires a management of monitoring for quality and tests. The coil system consists of 20 planar and 50 non-planar coils. They are supported by a pentagonal 10 m diameter, 2.5 m high coil support structure (CSS). The CSS is divided into five modules. Each module consists of two equal half modules. The manufacturing status of the CSS and the main project management and technical challenges will be presented. The lessons learned in the large scale production of this difficult kind of support structure will be presented as relevant experience for the realization of similar systems for future fusion devices, such as ITER.

To expand CERN testing capability to superconducting devices that cannot be installed in existing test facilities because of their size and/or mass, CERN is building a new cryogenic test facility for large and heavy devices. The first devices to be tested in the facility will be the S-FRS superconducting magnets for the FAIR project that is currently under construction at the GSI Research Center in Darmstadt, Germany. The facility will include a renovated cold box with 1.2 kW at 4.5 K equivalent power with its compression system, two independent 15 kW liquid nitrogen precooling and warm-up units, as well as a dedicated cryogenic distribution system providing cooling power to three independent test benches. The article presents the main input parameters and constraints used to define the cryogenic system and its infrastructure. The chosen layout and configuration of the facility is presented and the characteristics of the main components are described.

Copper-to-superconductor ratio O/SC ratio) is an important design parameter for a conductor for a high-current-density magnet. In this paper its influence on stability is studied, focusing on the disturbance due to a conductor motion. It is pointed out that minimum quench energy (MOE) is not significantly dependent on the Cu/Sc ratio and that is it difficult to explain the experimental results on training characteristics of SSC conductors with Cu/Sc ratios of 1.2 and 1.5 in terms of the dependence of MOE on the Cu/Sc ratio. In this paper, experimental results for SSC conductors are investigated by estimating the movable length of the conductor.

The cost of superconductor material is a significant portion of the total cost of an SMES (Superconducting Magnetic Energy Storage) system. The mass of superconductor required to store a given amount of energy is a function of the magnet structure. Five magnetic structures applicable for SMES are examined in this paper from the viewpoint of their energy storage capacities along with the peak field magnitudes. Two force-balanced structures are analyzed and compared.

In most magnetic resonance imaging (MRI) systems, pulsed magnetic gradient fields induce eddy currents in the conducting structures of the superconducting magnet. The eddy currents induced in structures within the cryostat are particularly problematic as they are characterized by long time constants by virtue of the low resistivity of the conductors. This paper presents a three-dimensional (3-D) finite-difference time-domain (FDTD) scheme in cylindrical coordinates for eddy-current calculation in conductors. This model is intended to be part of a complete FDTD model of an MRI system including all RF and low-frequency field generating units and electrical models of the patient. The singularity apparent in the governing equations is removed by using a series expansion method and the conductor-air boundary condition is handled using a variant of the surface impedance concept. The numerical difficulty due to the "asymmetry" of Maxwell equations for low-frequency eddy-current problems is circumvented by taking advantage of the known penetration behavior of the eddy-current fields. A perfectly matched layer absorbing boundary condition in 3-D cylindrical coordinates is also incorporated. The numerical method has been verified against analytical solutions for simple cases. Finally, the algorithm is illustrated by modeling a pulsed field gradient coil system within an MRI magnet system. The results demonstrate that the proposed FDTD scheme can be used to calculate large-scale eddy-current problems in materials with high conductivity at low frequencies.

Abstruct -The eddy currents induced on the super conducting magnet (SCM) vessels of magnetically levitated vehicles (MAGLEV) have been analyzed. A 3D eddy current analysis code, based on a finite element method with thin shell approximation, is developed and verified through a mock-up SCM experiment. Through a coupled electromagnetic and mechanical analysis under SCM vibration, a SCM structure with low resistivity material coating on the inner vessel of SCM is found to be suitable for the significant reduction of helium evaporation due to eddy current loss.

Although many cryostats have been designed with refrigerated shields covered by multilayer thermal insulation, the theory behind it has not yet been fully developed. In this paper, a thermodynamic analysis is made to minimize the power consumption of cryogenic systems containing refrigerated shields, considering all the design variables (temperatures, number of layers/cm present in the insulation and refrigeration efficiencies). In what concerns the temperature optimization, the theory of Eyssa and Okasha is extensively revised and improved, and analytical solutions are presented. We also analyze several typical cases concerning some optimization options.

The primary issue facing Nb 3 Sn cable-in-conduit conductors (CICCs) has been degradation, often observed during electromagnetic cycling, in the current sharing temperature, n-index, and critical current, in respect to measured strands values, due to strain effects. In the last years, work performed mostly relating to fusion magnet technology has led to a better understanding of the parameters required to improve the constraints imposed by the brittle nature of the Nb 3 Sn filaments, such as cables low void fraction and long twist pitch sequence. On the other hand, experimental campaigns on bent Nb 3 Sn wires, pre-compressed into a stainless-steel jacket, have shown that an appreciable decrease in the n-index values already occurs at the strand level, well below the irreversible mechanical load regime for filament breakage. This result is explained, with the support of simulation results, taking into account the broadening of the critical current distribution on wires cross section due to the presence of the jacket and to bending strain. Considering the CICC's layout impact on their overall performances, the effective resemblance between pre-compressed bent wires and strands inside cables is emphasized, and an innovative interpretation of cabled conductors test results is given, suggesting a tool to predict their performances in terms of the n-index versus critical current relation of constituting strands, characterized under simultaneous pre-compression and bending strain. Index Terms-Cable-in-conduit conductors (CICC), current sharing temperature, Nb 3 Sn strain degradation, superconducting magnets.

An undulator based positron source is a baseline for the International Linear Collider (ILC). The HeLiCal collaboration in the UK is carrying out an R&D programme on a short period superconducting helical undulator with the goal to develop modelling, measuring and manufacturing techniques. Several undulator prototypes have been built and successfully tested. This paper summarizes the results of the R&D phase of the project.

To achieve high luminosity at the collision point of the Compact Linear Collider (CLIC) the normalized horizontal and vertical emittances of the electron and positron beams must be reduced to 500 nm and 4 nm before the beams enter the 1.5TeV linear accelerators. An effective way to accomplish ultra-low emittances with only small effects on the electron polarization is using damping rings operating at 2.86 GeV equipped with superconducting wiggler magnets. This paper describes a technical design concept for the CLIC damping wigglers.

To explore the limits of layer wound (RE)Ba2Cu3O7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment > 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.

SuperKEKB is an upgrade project of KEKB to increase its luminosity to 8 x 10 35 cm −2 s −1 based on the nano-beam scheme. In SuperKEKB, one of a key element is a final-focus system; it reduces í µí±’ − /í µí±’ + beam size to 50 nm in vertical and 10 μm in horizontal direction at an interaction point (IP). The system consists of eight superconducting quadrupole magnets and four quadrupoles are aligned on the each beam line. The quadrupole, QC1P(QC1E), which is located at the closest position to the IP on the í µí±’ + (í µí±’ −) beam line, generates a field gradient of about 70 T/m. An inner diameter of coil and a magnetic length for QC1P(QC1E) are 25(33) mm and 334(373) mm, respectively. The production of all quadrupole magnets are completed. To confirm their field qualities, we performed magnetic measurement for each magnet in advance to be integrated into cryostats on the beam lines. In the measurement, the quadrupoles were cooled down to 4.2 K in a test vertical cryostat and magnetic field were measured with harmonic coils. The amplitudes of higher order harmonics for all magnets met requirements from beam optics design. In this paper we describe the measurement results.

The design and performance of an electron spin resonance spectrometer operating at 3 and 9 GHz microwave frequencies combined with a 9-T superconducting magnet are described. The probehead contains a compact two-loop, one gap resonator, and is inside the variable temperature insert of the magnet enabling measurements in the 0-9 T magnetic field and 1.5-400 K temperature range. The spectrometer allows studies on systems where resonance occurs at fields far above the g 2 paramagnetic condition such as in antiferromagnets. The low quality factor of the resonator allows time resolved experiments such as, e.g., longitudinally detected ESR. We demonstrate the performance of the spectrometer on the NaNiO 2 antiferromagnet, the MgB 2 superconductor, and the RbC 60 conducting alkaline fulleride polymer.

We first present a review of the existing analytical equations for electromagnetic forces and stress in a sector coil quadrupole, evaluating their extent of application in function of the coil geometrical layout. We analyze the distribution of stress provided on the coil retaining structure as well as on the coil mid plane, this one related to the degradation of critical current in the superconductor. We focuse on the maximum compressive stress dependence on the magnetic gradient at short sample conditions, considering two possible low temperature superconductors: Nb-Ti and Nb 3 Sn. In the last part the effect of an iron yoke on the magnetic field and forces is presented, proposing a correction of the critical current density expression when an infinite permeable iron yoke is used.

High-Field MRI provides high resolutions, welldefined chemical shift spectra and large data acquisition rates, and may bring about a paradigm shift in medicine through the in-vivo observation of metabolism. An 11.7 T whole body MRI magnet, for example, should be able to observe metabolic reactions occurring in a human body in addition to producing very precise images of body structures. At this field 13 C-NMR and biochemical reactions of organic molecules can be detected and analyzed in-situ. Then, organs, tissues, vessels and biochemical processes responsible for irregularities in question will be identified. However, an 11.7 T MRI magnet with a bore diameter of 900 mm is a big challenge to the present magnet technology. Field strengths, magnet sizes and superconducting materials to be needed for future high-field MRI are described.

The production of high magnetic fields using low temperature superconductors (LTS) has become common place. However, large magnet sizes and associated high cooling costs have often precluded the full utilization of these research capabilities. Recent advances in internal Sn superconductors and cryogen free technology have opened up a new era in superconducting magnet development. Ultra-compact, laboratory sized magnets producing fields up to 22 Tesla are available. This new class of high field magnet weighs under 200 kg and is suitable for general laboratory installation. In addition, extremely compact, high field, split pair magnets with open access are now operating at the elevated temperature of T = 4 2 K. Beyond conventional wet magnet technology, there is a growing trend to utilize cryogen free technology. Cryogen free magnets do not require liquid Helium baths and, with the addition of active shielding, both the experimental sample access and siting availability is improved. The influence of enabling technologies required to realize the above practical applications for high field, superconducting magnet systems is described.

ABSTRACT We have investigated critical current Ic properties of 600 A/cm-class GdBa2Cu3O7-δ (GdBCO) coated conductor (CC) deposited on IBAD template. 2.5 μm thick GdBCO layer has been obtained by pulse laser deposition without degradation of critical current density by an improved heating condition in reel-to-reel deposition process. This enables stable production of long length CC with Ic (77 K, self-field) of 600 A/cm-w. In-filed Ic has also shown high value e.g., Ic@77 K, 3 T=33 A/cm-w, Ic@20 K, 27 T=107 A/cm-w. These experimental results obtained in a wide range of bias conditions of temperature T, magnetic field B and field angle θ are useful as a fundamental data for design of superconducting devices such as coil winding and magnet. Furthermore, we have also shown that our proposed analytical expression of electric field vs. current density (E-J) characteristics agrees well with the experimental results. This analytical expression allows us to predictIc-B-T property as well as E-J characteristics at arbitrary conditions of B and T.

ABSTRACT Superconductors for high field magnets should have high mechanical strength, high Young modulus as well as high critical current density. The optimization of these properties is very important in the design of a magnet and its conductors. In case of high field solenoids, the main factor limiting the coil current is the mechanical properties of the conductors. A new optimization procedure for conductors is introduced, starting from the competition between the transport properties and the mechanical properties. The balance between mechanical and transport properties are calculated depending on the coil diameter and on the applied magnetic field, and examples of applications to Bi2223 tapes are presented.

To explore the limits of layer wound (RE)Ba 2 Cu 3 O 7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment > 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.

This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/hightemperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF.

We first present a review of the existing analytical equations for electromagnetic forces and stress in a sector coil quadrupole, evaluating their extent of application in function of the coil geometrical layout. We analyze the distribution of stress provided on the coil retaining structure as well as on the coil mid plane, this one related to the degradation of critical current in the superconductor. We focuse on the maximum compressive stress dependence on the magnetic gradient at short sample conditions, considering two possible low temperature superconductors: Nb-Ti and Nb 3 Sn. In the last part the effect of an iron yoke on the magnetic field and forces is presented, proposing a correction of the critical current density expression when an infinite permeable iron yoke is used.

Pzazzlvss ||||||lWllllllllIllllNIIUIIHIIIPIINIIIIMill CERN LIBRHRIES, GENEWR dipole·sextupole corrector magnet are given as examples. dipole magnet, a main quadrupole prototype and a combined into the causes of measured field imperfections can be deduced. A model Although the uniqueness of the results remains uncertain, useful insights of a least-squares minimization using the Levenberg-Marquard algorithm. unwanted multipole terms. The inverse problem solving is done by means field problem is formulated in order to explain the origin of the content of superconducting magnet for the Large Hadron Collider (LHC) an inverse After measuring the magnetic field of a model or prototype Abstract S. Russenschuck, T.