Conceptual Design and Sensitivity Analysis of MRI Magnets from REBCO HTS Tapes

An actively shielded wide-bore magnet system has been designed for magnetic resonance imaging. The gradient-based optimization solver of COMSOL Multiphysics has been used to obtain an optimum geometrical arrangement of symmetrical electromagnets in the magnetic resonance imaging (MRI) system. To generate a high and homogeneous magnetic field, we employed a second-generation rare-earth barium-copper-oxide (REBCO) high-temperature superconductor (HTS), which was wound into 10 double pancake coils (DPC). The dimensions of the DPC sets have been chosen considering the size of REBCO HTS tapes, and the optimized design solution provides magnetic field, stray field, and current passing through the HTS tapes on each DPC set. The design details of a 1.5 T actively shielded magnet as well as the sensitivity analysis of the inhomogeneity, stray field, and currents with respect to coil positions have been presented. Optimum parameters for various designs are listed. The inhomogeneity of 1.23 ppm in the 200 mm diameter of spherical volume (DSV) and a stray field of as low as 0.05 G outside of the 5 m distance were achieved. Additionally, a low peak field of 2.40 T in DPC sets has been accomplished. © 2002-2011 IEEE

Taşıma akımının tip-II süperiletkenlerin pimlenmeye bağlı manyetostriksiyon üzerindeki etkisi

Teorik olarak taşıma akımının ve uygulanan manyetik alanın tip-II süperiletkenlerin manyetostriksiyonu üzerindeki etkisini araştırdık. Bir süperiletken levha örneğinin manyetostriktif tepkisini incelemek için, mevcut çalışmada numunenin üç manyetik geçmişi dikkate alınmıştır: (1) sıfır alan soğutmasından sonra uygulanan taşıma akımı, (2) akım ve alan aynı anda uygulandığında, (3) akım mevcut kritik durumda uygulanır. Önerilen modelde, yeterince küçük taşıma akımına ve uygulanan manyetik alana maruz kalan levha içindeki akı profilini hesaplamak için üstel kritik durum modeli ve Bean modeli kullanılmıştır. Bu manyetik profil açısından iç gerilme ve manyetostriksiyon için basit ifadeler türetilmiştir.We investigated theoretically the influence of the transport current and applied magnetic field on the magnetostriction of type-II superconductors. In order to study the magnetostrictive response of a superconducting slab specimen, three cases of magnetic history of the sample are considered in the present work: (1) the transport current applied after zero-field-cooling, (2) the current and field are applied simultaneously, (3) the current is applied at the remenent critical state. In the proposed model, the exponential critical state model and the Bean model is employed to compute the flux profile within the slab subjected to sufficiently small transport current and applied magnetic field. Simple expressions for the internal stress and the magnetostriction in terms of this magnetic profile are derived. The magnetostriction curves versus the transport current and applied field are presented

AC Loss Analysis of HTS Pancake Coil of Coated Superconductors with Ferromagnetic Substrate

The influence of the ferromagnetic substrate on the AC loss of an HTS coil is extensively investigated by the finite element method. The model assumes the utilization of the coated conductors with a ferromagnetic substrate to construct the coil windings consisting of several turns. The calculations for both the strong and weak ferromagnetic layers were accomplished. The calculation is presented how to change the current distribution inside a superconducting region by the ferromagnetic layer.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [114F424]This study is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the grant number 114F424

Alternating-current losses in two-layer superconducting cables consisting of second-generation superconductors coated by U-shaped ferromagnetic materials

Cicek, Ahmet/0000-0002-7686-0045WOS: 000329565500080Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. the alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. the ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. in contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.Fund from the Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110T876]Project supported by the Fund from the Scientific and Technological Research Council of Turkey (TUBITAK) (Grant No. 110T876)

Numerical analysis of temperature distribution of superconducting coil stack

In this study, magneto-thermal studies were carried out by solving Ampere and heat conduction equations together in superconducting coil stacks wounded by coated conductors. The coil stack used in the calculations consists of 4 bobbins in the solenoidal structure and each bobbin has 100 windings. Coated conductors are 12mm in width, 100 µm in thickness and has 100 A critical current density. The two-dimensional temperature distributions of the coil stack for different current amplitudes were obtained. The effect of the distance between the coils and the frequency of the applied current on the coils temperature was investigated. As the current amplitudes increases, the temperature in the coils increases and as the distance between the coils increases, the temperature decreases

Magnetization of Gd diffused YBa2Cu3O7-x superconductor: experiment and theory

Ozturk, Kemal/0000-0002-8847-1880WOS: 000321898100083The magnetization of Gd diffused YBa2Cu3O7-x is measured by a vibrating sample magnetometer (VSM) at selected temperatures (5, 25, 50, 77 K). the experimental results for the magnetization are analyzed in the critical state framework involving Kim-Anderson field dependence J(c)(H) = J(c0)/(1 + vertical bar H vertical bar/H-0)(n) of critical current density and equilibrium magnetization M-eq. It is found that the inclusion of the equilibrium magnetization becomes more important at higher temperatures. At 77 K, the shape of the isothermal M-H hysteresis curve is governed by the equilibrium magnetization. Some superconducting parameters are determined by fitting the calculated curves to the experimental data

Numerical study of AC loss of two-layer HTS power transmission cables composed of coated conductors with a ferromagnetic substrate

This work includes the simulation of hysteretic AC losses in two-layer HTS power transmission cables made of second-generation high-temperature superconducting tapes with a ferromagnetic substrate subject to an oscillating AC transport current, calling upon the COMSOL Multiphysics nite-element software program and exploiting an AC/DC module. How the AC transport loss is in uenced by the arrangement of tapes, as well as the optimized design of superconducting power cables based on YBCO-coated conductors, are investigated. According to the radial arrangement of the tapes, four different orientations of ferromagnetic substrate are considered: 1) out-in (substrate of inner/outer layer facing outward/inward), 2) in-out (substrate of inner/outer layer facing inward/outward), 3) in-in (substrates of both inner and outer layers facing inward), and 4) out-out (substrates of both inner and outer layers facing outward). We found that the AC loss of the superconducting layer for the out-in arrangement is the lowest. We also compare our calculations with experimental results.This work includes the simulation of hysteretic AC losses in two-layer HTS power transmission cables made of second-generation high-temperature superconducting tapes with a ferromagnetic substrate subject to an oscillating AC transport current, calling upon the COMSOL Multiphysics nite-element software program and exploiting an AC/DC module. How the AC transport loss is in uenced by the arrangement of tapes, as well as the optimized design of superconducting power cables based on YBCO-coated conductors, are investigated. According to the radial arrangement of the tapes, four different orientations of ferromagnetic substrate are considered: 1) out-in (substrate of inner/outer layer facing outward/inward), 2) in-out (substrate of inner/outer layer facing inward/outward), 3) in-in (substrates of both inner and outer layers facing inward), and 4) out-out (substrates of both inner and outer layers facing outward). We found that the AC loss of the superconducting layer for the out-in arrangement is the lowest. We also compare our calculations with experimental results

A theoretical study for temperature dependence of levitation force of high-T-c superconductors

WOS: 000316932700007The temperature effect on the levitation force of a cylindrical type-II superconductor was investigated theoretically by solving the critical state equation. Analytical expressions are obtained for the levitation force versus increasing temperature for zero-field-cooled (ZFC). Examining the behavior of levitation force-temperature curves the critical parameters are the critical current density, lower critical field and the pinning strength. the calculation qualitatively agrees with the experimental results for high-Tc superconductors. Employing exponential decay of the critical current density we have reproduced temperature- levitation measurements published in the literature. Some important macroscopic parameters may be obtained by fitting the expressions introduced in this paper with the experimental data. (C) 2012 Elsevier B.V. All rights reserved.TUBITAK-BIDEBTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)One of the authors (F. I.) is grateful to TUBITAK-BIDEB for fellowship. We would like to thank to Mrs. Wendy Kasap for the linguistic corrections