Nb3Al superconductor has some advantages compared with traditional Nb3Sn superconductor, such as better stress characteristics, make it performance better at high field. However, the technology for Nb3Al magnet is not mature yet; the related technics are still under study. In this paper we will present the Nb3Al magnet technology progress in our lab. We have designed and manufactured an experimental coil with Nb3Al wire. Vacuum heat treatment which can reach 850 degree Celsius has also been done. To meet the demand of heat treatment, some techniques have been adopted in the coil manufacture, for example the bobbin is coated with Al2O3 ceramic which can withstand high temperature, and vacuum pressure impregnation technology is adopted to improve the performance of insulation structure. The coil is designed to generate 1 T in a 15 T background field and will be test actually, the results will also be analyzed. These will be done in the near future.

The rotating gantry for carbon cancer therapy is one of the attractive applications of magnets wound with coated conductors. Higher magnetic fields and less weights of coated-conductor magnets cooled by using cryocooler are their advantage as compared to copper magnets, whose magnetic fields are limited by the magnetic saturation of iron return yokes and whose weights are much larger because of the use of heavy iron return yokes. The possibility of operation at higher temperature is the advantage of coated-conductor magnets as compared to NbTi magnets. Meanwhile, the wide monolithic shapes of coated conductors should lead to large magnetization (screening current), which might substantially deteriorate the field qualities of magnets.
We studied the influence of the coated-conductor magnetization on field qualities of magnets for a rotating gantry. We designed the cross-section of a cosine-theta dipole magnet as well as that of a dipole magnet consisting of racetrack coils. Numerical electromagnetic field analyses, where considering the superconducting properties of the coated conductors, were carried out to obtain the temporal evolution of the current distribution (magnetization current or screening current) in each turn of the magnet. When carrying out the analyses, the temporal profiles of the current supplied to the magnet were determined based on the actual excitation schemes of magnets for a rotating gantry. From the obtained current distributions in the entire magnet, we calculated the magnetic field harmonics and estimated the field quality of the magnet. Higher harmonics normalized by the dipole were the order of 10^-4 at stages of the current profiles where irradiating carbon irons to a patient. They were stable enough and were reproducible in repeated excitations. The results of the analyses are encouraging the use of coated conductors in magnets of rotating gantries for carbon cancer therapy.

This work was supported by AMED and METI as Development of Fundamental Technologies for HTS Coils Project.

A new innovative Whole Body 11.7 T MRI magnet which is currently being manufactured at Alstom Belfort as part the Iseult/Inumac project, a French-German initiative focused on very high magnetic-field molecular imaging.
It will be installed in 2016 in a neuroscience research center with other very high field MRI equipment, operating in France at CEA Saclay since November 2006.
The whole Body 11.7 T MRI Magnet has external dimensions of 5 m in diameter and 5 m in length, with a stored magnetic energy of 338 MJ and an inductance of 308 H. 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 in driven mode, i.e. permanently connected to a power supply. The external cryoplant is connected permanently to the magnet and it provides pressurized Helium II at 1.8 K. The magnet facility has to operate 24 hours a day continuously for several years. Therefore all external components have been designed to avoid magnet discharge as much as possible in case of a failures from the mains, power supplies, liquefier, helium compressor, etc... In order to increase its reliability, the quench detection system is based on majority voting redundancy.
This paper describes the redundancy of power supplies system, the architecture of the magnet safety system, the high availability of the magnet control system and cryogenic supply. The issues about mains supply, the water cooling, the cryogenic plant and the Programmable Logic Controller (PLC) architecture will be presented.

We have been developing high-temperature superconducting (HTS) magnet system of heavy -ion accelerator for particle cancer therapy. A novel HTS cyclotron is designed to be more compact and have higher efficiency than the conventional heavy-ion synchrotron accelerator. The magnet system of the HTS cyclotron is composed of HTS split coils for isochronous field and HTS spiral sector coils for azimuthally varying field (AVF). High current density is required for the HTS magnet to realize the compact HTS cyclotron. Thus, a high-strength reinforcing structure for the HTS magnet against the large Lorentz force caused by the high current density is absolutely necessary to prevent the magnet deformation and maintaining the required high accuracy field.
In the previous study, a novel coil structure named “Y-based oxide superconductor and reinforcing outer integrated (YOROI) coil” was developed and tested at 4.2 K in 8-T backup magnetic field. The YOROI model coil showed no degradation after the excitation test with a maximum hoop stress of 1.7 GPa determined by the product of magnetic field, current density, and coil radius. The reinforcing structures of the HTS cyclotron magnet based on the YOROI coil was proposed and numerically simulated in the previous papers.
In this study, the reinforcing properties of the HTS cyclotron magnet were numerically compared with two reinforcing materials of Glass fiber reinforced plastics (GFRP) and stainless steel (SUS304). In addition, the coil deformation and magnetic field redistribution caused by the thermal contraction and Lorentz force of the HTS cyclotron magnet were also compared with the original design on the two materials.

This work was supported by a Grant-in-Aid for Scientific Research (A) from the Ministry of Education, Science, Sports, and Culture (No. 26249036).

We have been carrying out a feasibility study on the application of high temperature superconducting (HTS) coil to medical cyclotron systems for particle cancer therapy. It is expected to be compact, highly efficient, is able to extract high energy beam and to consume low less power. In cyclotron application, the high accuracy magnetic field distribution with isochronous field and azimuthally varying field (AVF) is required on medium plane of coil system for the stable acceleration of particles. In REBCO coils, large screening currents are induced in the REBCO tape by the radial component of the magnetic field. The magnetic field generated by the screening currents affects the magnetic field distribution for the cyclotron application in aspects of spatial field accuracy, temporal field stability, and field repeatability.
In previous study, in order to evaluate the effect of screening current in HTS coils, we developed the novel numerical simulation based on the finite element method, boundary integral equation and fast multipole method. Furthermore, we proposed and designed the magnet system of HTS cyclotron. In this study, we investigated the behavior of isochronous field and azimuthally varying field, which are affected by screening current in REBCO coil composing our designed HTS cyclotron system.

This work was supported by a Grant-in-Aid for Scientific Research (A) from the Ministry of Education, Science, Sports, and Culture (No. 26249036).

A HTS hybrid magnet wound with no-insulation(NI) racetrack double pancakes is fabricated, which is designed to generate 0.5T at 77K and 5.6T at 20K, the hybrid magnet utilizes 8 BSCCO pancakes and 2 YBCO pancakes. As the NI magnet is promising for high field application, it is necessary to test the current carrying ability and electrical-thermal stability of the magnet. In this paper, we test the performance of each pancakes at the operating temperature of 77K, the variations of voltage, magnetic field and temperature during charging are investigated. Then, assemble the pancakes into magnet, the difference and interaction between the quench characteristic of BSCCO and YBCO NI pancakes are taken into consideration to evaluate the performance of the magnet. Finally, the test results of the NI hybrid magnet are discussed.

In recent years, the research and development on ultra-high field MRI magnets wound with REBCO tape wires are in progress. The MRI magnets have to generate a highly homogeneous field to the order of sub-ppm. The configuration of an ultra-high field MRI magnet is design so as to eliminate the high-order coefficients of spherical harmonic expression on magnetic field around the center. Commonly, it is assumed that the current flows uniformly on the cross section of the coils. However, the REBCO tape wires has a REBCO superconducting layer of ~2.0 µm; nevertheless the thickness of the REBCO tape wire is ~100 µm. That is, the current flows in extremely small cross-sectional area of REBCO tape wire. Consequently, the magnet designed by the common way cannot generate the magnetic field of the expected homogeneity.
In this study, we developed a design configuration method for MRI magnet wound with REBCO tape wires, taking into account the REBCO superconducting layer. The developed method needs a lot of computation cost, therefore a co-processor, Intel Xeon Phi, is used for shortening the computation time.

This work was supported by the Ministry of Economy, Trade and Industry of the Japanese Government.

In MRI applications, the coil systems are fabricated from various combinations of the multiple coils in order to generate highly homogenous field. In the multiple coil systems using REBCO coils, the behavior of the screening current which deteriorates the field homogeneity depends on the pattern of transport current, the charging sequence of coils and various experienced magnetic field. Therefore, we have to investigate and clarify the behavior of the irregular magnetic field and the screening current in multiple coil systems in various operating environments. Moreover, we have to develop the reduction method for the irregular magnetic field generated by screening current taking advantage of the coil configuration and charging sequence. In previous study, we experimentally and numerically clarified the different behavior of irregular magnetic field in the charging sequence of coils in REBCO multiple model coil.
In this study, we calculated the irregular magnetic field in our designed REBCO multiple coil for MRI applications under the various charging sequences using our developed three-dimensional numerical simulation based on a finite element method (FEM) and fast multiple method (FMM). From the numerical results, we discuss about the behaviors of irregular magnetic field in various operating conditions in the REBCO multiple model coils.

This research was supported by the Ministry of Economy, Trade and Industry of the Japanese Government, and Grant-in-Aid for Scientific Research(C), the Ministry of Education, Science, Sports and Culture (No.25420253)

Development of an HTS magnet wound with REBCO coated conductor for ultra-high field MRI is in progress. Our final targets are 9.4 T MRI systems for a whole-body and for brain imaging. Since REBCO-coated conductors feature high mechanical strength under a tensile stress and high critical current density, superconducting magnets could be smaller by using REBCO coils. Superconducting magnets for MRI requires homogeneous and stable magnetic field. The homogeneity of the magnetic field is highly dependent on the size and current density of the coils. Furthermore, in the REBCO magnet, the screening-current-induced magnetic field that changes the magnetic field distribution of the magnet is one of the critical issues. In order to evaluate the magnetic field homogeneity and the screening-current-induced magnetic field of the REBCO magnet, a conduction-cooled REBCO magnet with a room temperature bore of 200 mm was fabricated and tested. The REBCO coil is composed of 12 single pancake coils. The central magnetic field was as high as 1.05 T at 300 A. This paper describes the design of the conduction-cooled REBCO magnet and test results of the magnetic field homogeneity.

This work has supported by the Ministry of Economy, Trade and Industry of the Japanese Government.

In recent years, the research and development on applications of REBCO superconducting coil to the high field magnets for MRI applications are in progress. In REBCO coils, large screening currents are induced in the winding tape by the radial component of the magnetic field. The screening currents lead to the serious problem in REBCO magnets for MRI applications in which very high field quality is required. Thus, the irregular magnetic field generated by the screening currents affects can deteriorate the field quality spatially and temporally. Therefore, the evaluation of screening current in REBCO coil is essential for the design and development of coil systems for MRI applications. In previous study, we investigated current distribution in REBCO tape and spatial and temporal behavior of magnetic field using our developed three-dimensional numerical simulation code using finite element method (FEM) and fast multipole method (FMM).
In this study, we designed various high-field and homogenous-field REBCO coils and numerically investigated the irregular magnetic field generated by screening current in these REBCO coils. And we discuss the irregular effect of magnetic field generated by screening current in REBCO coil from the aspects of shape and arrangement of coil windings and field.

This work was supported by the Ministry of Economy, Trade and Industry of the Japanese Government.

Hyperpolarization (HP) technique can temporarily enhance the magnetic resonance (MR) signal of nuclei used in MR imaging by several orders of magnitude. Such HP enhanced signals enable imaging of key biochemical processes in vivo with unprecedented sensitivity and resolution, what particularly is beneficial for detection of the ¹³C isotope. However, measurements are challenging because the MR signal is non-renewable, decays with T₁ relaxation, and is already depleted during excitation. Any methods that improve the intrinsic signal-to-noise ratio (SNR) of the MRI set up can ultimately be leveraged for higher sensitivity and/or spatiotemporal resolution. We report on development of Cu and YBCO receive MRI coils, which can provide very significant SNR gain for _¹³C detection at 7 T, due to lower than for protons (¹H) Larmor frequency of ¹³C nuclei therefore lower body loss compared to ¹H ions. Our objective is to investigate the practical limit of such SNR gain for the 7T MRI ¹³C (75 MHz) receiver probe. The coils were designed and integrated with a custom-made cryo setup (pulsed tube) for small animals (compatible with 7T Bruker scanner) and a low-loss matching, tuning, and decoupling circuitry. High frequency laminate with ε=2.2 and thickness of 0.381 mm was used for the Cu coil fabrication. For YBCO prototype, films on both sides of a 0.33 mm thick Al₂O₃ (ε=10.4) wafer were patterned using optical lithography and wet etching. Calculations and measurements of SNR gain from cooling included cryostat and electronic losses, in addition to coil and body resistances. SNR gains obtained at 7T for cooled Cu and HTS ¹H coils (18-20 mm in diameter) over room temperature copper, tested on rat phantoms at 300 MHz, were 80-100% (~6 dB) and 150-170% (~8 dB), respectively. We have compared SNR gain performance of ¹H and ¹³C Cu coils. It turned out that the optimized for L/C (butterfly) designs of 75 MHz 13C coil can achieve the same gain for much larger coil compared to ¹H (24x34mm vs. 18-20mm, respectively). For the ¹³C coil of the same size as the ¹H coil, it was found that almost 400% SNR gain (for rat brain load) can be obtained compared with only 90-100% SNR gain achievable for ¹H coil. Further increase of the SNR gain (when using smaller coils) will require a cryogenic preamplifier and also further reduction of the tuning/matching circuit losses.

We are developing superconducting magnets for MRI with REBCO superconducting tapes. MRI magnets need uniformity of produced magnetic field within 1 ppm order in time and space. The disturbance in magnetic field is mainly caused by the induced shielding current in REBCO superconducting tapes. We have studied on the decay of the shielding current induced in a REBCO superconducting tape itself and also have proposed how to reduce the shielding current. However, for actual superconducting magnets, a current capacity of REBCO superconducting tapes should be enhanced from the viewpoint of the protection of superconducting magnets. We proposed the configuration of transposed parallel conductors so as to increase the current capacity of HTS tapes without the increment of ac loss. We adopted parallel conductors with REBCO tapes to build a 66/6.9kV-2MVA superconducting transformer operating at 65 K. Now we try to apply them to dc superconducting magnets for MRI. Here we have to reconsider the applicability of parallel conductors to dc superconducting magnets in which uniformity of magnetic field is required. That is strictly even current sharing among the constituent tapes is required. In this study, we investigated the current sharing properties among the tapes in 3-strand parallel conductors with REBCO superconducting tapes. Practical REBCO superconducting tapes have small n-values on the I-V curves and also dispersion in Ic. Taking into account of them, we numerically calculated the branch current ratios with a frequency as a parameter. As a result, we found out that the difference in n-value and Ic among the constituent tapes led to uneven current sharing, especially at low frequency. The more difference in n-value and Ic, the more unbalance in current sharing. In this conference, we will discuss on that.

A part of this work is supported by the Minister of Economy, Trade and Industry (METI) as "Development of Fundamental Technologies for HTS Coils".

We are developing REBCO superconducting magnets for MRI. We intend to operate them in subcooled liquid nitrogen at 65 K. Superconducting magnets for MRI need uniformity of produced magnetic field within ppm order in time and space. The disturbance is mainly caused by the induced shielding current in REBCO superconducting tapes. That corresponds to the magnetization of the tapes. The shielding current also decays due to flux creep and/or flux flow. That corresponds to the relaxation of magnetization. Therefore it is necessary to reduce the magnetization itself for the uniformity of produced magnetic filed. We proposed the method to reduce the magnetization and the ac loss of REBCO superconducting tapes. It is the combination of scribing tapes into a multifilamentary structure and specially winding of the tapes. We successfully applied the technique to the construction of a 66/6.9kV-2MVA superconducting transformer in a national project in Japan. In this study, we applied the technique to develop dc superconducting magnets for MRI. We fabricated 2-pieces of small test coils with REBCO superconducting tapes. One was wound with a non-scribed tape and the other was with a laser-scribed tape into a 4-filament structure. We inserted them inside a NbTi superconducting magnet individually. Bath-cooling them down to 65 K with subcooled liquid nitrogen and applying a dc bias magnetic field of 1, 0.5, 1 and 2 T, we applied transport current to them step by step and observed the magnetic field at the coil center by a hall probe with high accuracy. Though, in both the coils, the magnetic field followed the sweep and hold of transport current with a delay, the drastic difference between them was revealed. The influence of shielding current to the produce magnetic field in the scribed one was smaller than the non-scribed one. In addition the decay of shielding current, that is the relaxation of magnetization in the scribed one appeared to be faster than the non-scribed one. In this conference we will show the effect of scribing in superconducting magnets for MRI.

A part of this work is supported by the Minister of Economy, Trade and Industry (METI) as “Development of Fundamental Technologies for HTS Coils”.

We are developing superconducting magnets for MRI with REBCO tapes. We intend to operate superconducting magnets in subcooled liquid nitrogen at 65 K. It will bring us high stability due to a large heat capacity at high operating temperature and very good cooling with liquid nitrogen. To realize a few T superconducting magnet at 65 K, we are developing REBCO superconducting tapes with artificial pinning centers. We have already attained Ic of 616 A/cm at 65 K and 3 T. Further, for the uniformity of produced magnetic field in time and space, we have to clarify and reduce the influence of shielding current induced by the perpendicular component of applied magnetic field to a tape face. To investigate that, we made small test coils with REBCO tapes. REBCO tapes 5 mm wide and 30 m long were wound into multilayered solenoid coils with an inner diameter of 78 mm. Test coils were inserted into a NbTi superconducting magnet, which provided a dc bias magnetic field of 0 to 2 T. Test coils were cooled down to 65 to 77 K with subcooled liquid nitrogen. Transport current was increased up to around Ic step by step with an interval of 10 to 20 A. Using a hall probe with a high accuracy, we observed the magnetic field at the center of each test coil individually. The center field increased with a time lag against the variation of transport current due to the induced shielding current. It was revealed that the apparent decay time constant of the shielding current increased with magnitude of transport current and decreased abruptly below around Ic. It seems to originate from the equivalent resistance of the REBCO tapes, which is calculated from the I-V characteristics expressed with a power law. In this paper, we will show such an interest phenomena and propose a new operation method of REBCO coils for MRI

A part of this work is supported by the Minister of Economy,Trade and Industry(METI) as"Development of Fundamental Technologies for HTS Coils".

Achieving considerably homogenous magnetic field inside a given volume so called diameter of sphere volume (DSV) between magnetic resonance magnet coils is particularly important for the full body imagination to be scanned. Therefore, the design and the optimization of the magnet geometry has to be implemented accurately by employing the numerical calculation method. In this work, we have tried to design a MRI magnet coil to be able to generated 0.5 T magnetic field and to optimize with respect to the minimum volume of coils configuration. The finite element method have been utilized for the design and as well the linear programing method for the optimization. The optimized coil configuration parameters and the magnetic field distributions have been introduced

Project supported by the Fund from the Scientific and Technological Research Council of Turkey (TUBITAK) (Grant No: 114F424).

Current research has identified a need for greater magnetising fields during vibrating sample magnetometer (VSM) measurements and other measurement options. We present here the methodology involved in our development of a VSM system with 22 T superconducting magnet, a unique system and the highest field combined with a VSM anywhere in the world.
Recent developments in HTS conductors have allowed greater reliability than previous coils made from YBCO and BISCO and thus facilitate the consistent achievement of higher magnetising fields at the sample with operation at 4.2 K rather than 2.2 K.
Cryogenic Ltd wind HTS coils in both solenoid and pancake forms with an emphasis on solenoids, since they have been found to give a more reliable performance with less thermal transfer to the surrounding liquid helium. The 22T VSM system has been developed using 2G YBCO coated and BSSCO tape which exhibit critical currents up to 5 times greater than those seen in YBCO and BISCO at 4.2 K.

Almost the only opportunity to expand the synchrotron radiation (SR) spectrum range to rigid part of SR sources is to install of superconducting high field magnets. The SR spectrum property is defined by product: ~E2B, where E-energy of electrons in a storage ring, B- magnetic field value in a radiation point. Use of a superconducting material for magnet production allows to receive magnetic field much higher than with using traditional materials with normal conductivity or permanent magnets. One of opportunities of an essential expanding the spectrum and an intensity increasing of SR is installation of multipole superconducting high field wiggler. In the report the description of the superconducting wiggler with field of 7.5 Tesla made by Budker INP and installed on the storage ring of CAMD LSU (USA) is given. Wiggler consists of 11 main bending magnets with sign alternating magnetic field and amplitude of 7.5Tesla and four side poles (two on each end of the magnet array) which are intended for receiving zero of the first and second field integrals in the longitudinal direction at any field level of the main poles. The main attention at design and production of magnetic system of the wiggler was paid to the magnetic field quality at all field levels. Results of field magnetic measurements with use of Hall probes are presented. Dynamic behavior of the first and second field integrals during ramping field up and down measured with use of a method of the stretched wire with current are discussed. The wiggler was installed and successfully commissioned on the CAMD LSU storage ring in 2013.

We are grateful to scientific director Jhon Scott and associate director CAMD LSU Vic Suler for the problem definition and for interest in the course of works, Rupal Amin and Morris Kevin for the technical support during installation and commissioning of the wiggler on the CAMD LSU site.

This work was supported in part by United States National Science Foundation grants PHY-09-58726 and PHY-11-02511

HTS shield prototype for electron cooling system of charge particle beams is presented in this paper. The shield has 500 mm length and designed for the magnetic field up to 0.2 T.
Research of the shield was carried out under different quasi-stationary operating conditions. It is shown that selection of the optimal position of the HTS shield may significantly expand the scope of the magnetic field homogeneity. HTS shield was proposed to obtain the required magnetic field homogeneity (about 10^-5) in the 6 meters length solenoid of the electron cooling section which will be installed in the heavy ion collider of the NICA project (JINR, Russia).

The NICA (Nuclotron-based Ion Collider fAcility) project is now under realization at the Joint Institute for Nuclear Research. The main goal of the project is a study of hot and dense strongly interacting matter in heavy ion (up to Au) collisions at the centre-of-mass energies up to 11 GeV per nucleon. Two modes of operation are foreseen, collider mode and extracted beams, with two detectors: MPD and BM@N. The both experiments are in preparation stage. A study of spin physics problems with extracted and colliding beams of polarized deuterons and protons at the energies up to 27 GeV (for protons) is foreseen at the SPD detector, which is under design at the present time, The NICA Complex is based on the use of different types of superconducting magnets. We briefly review their general status and describe more detailed set of the magnets that should provide operation of the facility in polarized proton and deuteron mode.

The Future Circular Collider (FCC) study at CERN is investigating the feasibility of a future proton-proton collider with center of mass energy of 100 TeV and tunnel circumference of 100 km. Arc dipoles with 50 mm aperture and 16 T field are required for this application. Among the possible magnetic layouts, block-coils offer attractive features in terms of conductor packing, separation between high-field and high-stress locations, use of flat cables and fewer coil parts of simple geometry. In order to assess these potential advantages, the HD series of block-coil models was designed, fabricated and tested at LBNL. These models achieved the highest dipole field to date both in technology tests and accelerator configurations. The current record for a magnet with accelerator features is HD2, with 36-43 mm aperture depending on the assembly configuration, and a maximum field of 13.8 T at 4.5K. In this paper, we discuss the possible options for extending the HD2 design to an aperture of 50 mm and a short sample dipole field above 18 T at 1.9K, suitable for a first demonstration of the FCC baseline parameters.

This work was supported by the DOE Office of High Energy Physics under contract number DE-AC02-05CH11231

First few nested superconducting multipole magnets to be used in the Super Separator Spectrometer (S3) device which is under construction at the GANIL laboratory in France have been manufactured and tested. The multipole magnets are based on a novel winding configuration for transverse magnetic fields of given multipole order, which closely approximates a pure cosine(n-Theta) current density distributions over the entire length of the coil including the coil ends. The windings are implemented as stacked saddle coils, a patented configuration, in which multiple conductor layers are inserted in precisely machined grooves. The resulting superconducting saddle coils achieve unprecedented magnetic field uniformity. In addition to highly suppressed systematic field errors, the resulting coils offer insignificant random field errors.
Multipole magnet measurements at room temperature and at of 4.2K have been performed. Tests have shown that the magnet meets the stringent magnetic field quality requirements and also that the magnet does not require any quench training which is unprecedented. We will present the novel coil design, practical implementation and discuss the performance of the magnets at final operating conditions.

This work partially supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357 using resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.

For the hadron version of the Future Circular Collider (FCC) the most costly component is the high field dipole magnet. In the present FODO lattice about 4500 units of 14.3 m in effective length are arranged in groups of eleven between the focusing and defocusing quadrupoles. The length of the units is the maximum that can be reasonably envisaged for transport and handling. It is proposed to replace these groups of dipole units by a single entity of about 165 m in length that is assembled in the tunnel. In such an arrangement the 22 end windings would be replaced by two end connections of a different type, thereby increasing the filling factor and decreasing both the nominal field required for a given collision energy and the quantity of superconducting cable to be purchased. The new end connections would be longer, but could be entirely composed of Nb-Ti cables, or a combination of Nb-Ti cables and YBCO tapes. It is also proposed to incorporate HTS poleface windings for control of multipoles. Furthermore, if deemed to be useful, a gradient component could be included in the dipole field to allow the shifting of some of the focusing power to the arc and make way for the replacement of the present Nb3Sn quadrupoles by relatively conventional Nb-Ti magnets in a partially combined function lattice. Technological aspects of the concept are discussed.

The US LHC Accelerator Research Program (LARP) has been developing Nb3Sn quadrupoles of progressively increasing performance for the high luminosity upgrade of the Large Hadron Collider. The High-field Quadrupole (HQ) models, designed to operate at 170 T/m in a 120 mm aperture, are the last step in the R&D phase supporting the development of the new IR Quadrupoles (MQXF). Three series of HQ coils were fabricated and assembled in a shell-based support structure. Tests of the first series of coils revealed the necessity for further optimization of the design and fabrication process. These changes were systematically implemented in the second-generation coils, leading to significantly improved performance. Finally, a third set of coils was fabricated and assembled in the HQ03a model to consistently apply the optimized design features, and assess performance reproducibility. In this paper, we report on the quench performance HQ03a, including training history, quench origin and propagation, protection, temperature and ramp rate dependence studies.

Work supported by the U.S. Department of Energy through the US LHC Accelerator Research Program (LARP). Additional support by EU FP7 HiLumi LHC - Grant Agreement 284404.

The dimensions of Rutherford cables have an implication on the coil cross section design in accelerator magnets such as the Nb₃Sn, low-β, Interaction Region quadrupole magnets MQXF being developed by the US LHC Accelerator Research Program (US LARP). A cable, after fabrication, often requires insulation, coil winding, curing, and a formation heat treatment (HT) which converts physically separated Nb and Sn in an as-drawn wire to form the superconducting phase. This phase transformation during the heat treatment drives the cable width, mid-thickness, and keystone angle in a heat treated coil to be considerably different from the cable specifications that are defined in the as-fabricated state and used for qualification purposes. In this study, we shall analyze coil cross sections to compare the dimensions of cables in a reacted and impregnated coil to those measured on cables reacted in tooling that leave the cables un-constrained. This will provide feedback or justification for the assumed conductor dimensions in the second generation MQXF coil design.

Research supported by DOE via the US-LARP program and by the High Luminosity LHC project.
Two of the authors (IP, EFH) gratefully acknowledge the support granted by the USLARP Toohig Fellowship.

The US LHC Accelerator Research Program (USLARP) is developing low-β, Interaction Region Nb₃Sn quadrupoles for the Hi-Lumi LHC upgrade. The 120 mm aperture HQ magnet series is the basis for the 150 mm aperture IR QXF quads to be implemented in the LHC upgrade. The design of the second generation magnet, HQ02, allowed the conductor to expand 2.7% in width and 5% in thickness during the Nb₃Sn heat treatment. The allowed for expansion reduces strain during heat treatment but may have allowed slight displacement of each turn which collectively may affect field quality. Field quality was previously measured in HQ02 with a new multi-layer circuit board probe and compared to design and similar HQ01 measurements. For the first time in a superconducting magnet, this work directly explores methods of measureing turn displacement and possibly correlating to measured field quality. HQ02 was water jet cut at locations in the magnet assembly corresponding to previous magnetic multipole probe measurements. From the coil cross sections the location of each turn was measured and input into a magnetic field model. Comparison between measured multipoles and simulated poles from measured turn displacement will be presented and discussed.

Research supported by the DOE via the US-LARP program and by the High Luminosity LHC project.
Two of the authors (IP, EFH) gratefully acknowledge the support granted by the USLARP Toohig Fellowship.

The FCC-hh presently under study at CERN will make use of 16 T superconducting dipoles for achieving 100 TeV p-p center-of-mass collision energy in a 100 km ring collider. A beam screen will shield the 1.7 K dipole cold bores from the 28 W/m/beam of synchrotron radiation, operating at 50 K as best compromise temperature among several different requirements, with the goal of reducing the wall-plug power consumption of the cryogenic system. In the LHC, a stainless steel beam screen with a 80 µm copper coating is used for the same purpose, kept at 20 K to minimize beam coupling impedance. However copper operating at 50 K might not provide low enough beam coupling impedance in the FCC-hh. It has then been proposed to reduce the beam coupling impedance by adding a thin layer of a High-Temperature Superconductor (HTS). Purpose of this paper is to describe the basic properties of a superconductor in the RF field induced by beam image currents and exposed to a high magnetic field, to study the validity of the approach and to identify the best candidate materials and coating processes.

High Temperature Superconducting (HTS) materials have been shown to be convenient and effective in shielding magnetic fields. Second Generation ReBCO HTS are manufactured as wide tapes with high critical current density at 77 K. The properties improve significantly as the operating temperature is lowered. It is however, more expensive to operate the magnetic shields at lower temperatures. To optimize the magnetic shield designs both in terms of their shielding efficacy and operating expenses, it is necessary to have AC loss data available at lower temperatures. For this study, we used a cryogenic helium circulation device that allows simultaneous magnetic shielding measurements and calorimetric magnetization AC loss measurements. Magnetic shielding characteristics and AC losses were measured on sample magnetic shields with cylindrical shape that are 5 cm in diameter and 20 cm in length fabricated from 40 mm wide 2GHTS tapes. The measurements were made at variable temperatures as low as 15 K. Shielding factors were measured in AC magnetic fields in frequency interval 5 – 400 Hz and magnetic field magnitudes up to 100 mT. The alternating magnetic field is generated by liquid nitrogen cooled copper coils that produce a uniform magnetic field over the test shields. The measurement protocol used and the results of shielding properties and magnetization loss measurements on single and double layer cylinders are discussed.


This work was supported by the Office of Naval Research under Grant N00014-14-1-0155 and by the
American Superconductor, who provided the superconducting material.

Hysteresis losses of five Nb3Sn ITER reference strands were investigated by means of magnetization loop measurements in a vibrating sample magnetometer (VSM). Samples in the form of a “mini-coil”, a small spiral consisting of 7 turns of the strand, were prepared and placed in the VSM in a homogenous magnetic field applied perpendicular to the strand’s length. The magnetization loops were recorded while continuously sweeping the applied field between two extreme values +Bm and –Bm, covering a wide range of maximum applied fields Bm in the experiments (from approximately 0.3 T to 10 T). On the basis of the loop with Bm = 10 T the dependence of the width of the magnetization loop on the magnetic field (deltaM(B)) was determined.

In the paper we compare the directly measured hysteresis losses and the losses calculated by integrating the deltaM(B) dependence determined from the 10 T magnetization loop.

We propose a suitable fitting function for the critical current density to describe the deltaM(B) dependence. Use of this fitting function leads for each strand to an excellent agreement with the experimentally determined hysteresis losses, magnetization and pinning force.

Disclaimer:
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

A theoritical coupled thermal, mechanical and electromagnetic simulation of a YBCO disk during pulsed field magnetization was performed and the simulated resulting magnetic field was compared to experimental measurements. Due to the symmetry of the problem, a 2D axisymmetrical modelling using Finite Element Method was chosen, and A and T-formulations were compared. One of the complexity of modelling superconducting bulks is the actual determination of the currrent path within the bulk and how the micro-structure may play a role in limiting the intensity of induced current. Assuming an isotropic material, the pure knowledge of the temperature distribution resulting from the local resistivity of YBCO allows to define the limitation of the intensity of persistent current. However, the induced current in conjunction with the applied pulsed magnetic field in addition to thermal induced local stresses which is very little studied may play a role in the local dissipation as well. In the present work, the influence of one or the combination of both phenomena is studied to determne how they may explain early onset of local normal-zone transition and some of the experimental results reported hereinafter.

Use of high temperature superconducting (HTS) magnets has been considered for reducing the size of a rotating gantry for carbon therapy. In recent carbon therapy, three-dimensional raster scanning is employed in which the depth dose-distribution is determined by beam energy. In order to accommodate the various beam energies multiple flattop operation is required for the gantry magnets. On each flattop the beam must be scanned laterally that requires good field stability of the magnets during the flattop. The HTS magnets, because of large shielding currents existed in the coated conductor, may have large field change during the flattop. In order to evaluate the field change during the flattop a small pancake coil wound by a coated conductor was fabricated and temporal field change was measured with operation patterns that simulate the multiple flattop operation. The measurement was made using a hall probe array and taken with various operation patterns that change field ramp rate prior to the flattops. The paper summarizes the measurement results and evaluates possible operation patterns with HTS magnets.

This work is supported by the Ministry of Economy, Trade and Industry (METI), Japan

Screening currents induced in HTS-wound magnets require special care during the design process as the impact of such currents can lead to severe degradation of the field properties.
The following article will focus on a screening-current simulation code implemented in Cast3M, a finite-element open-source software developed by CEA (French Alternative Energies and Atomic Energy Commission). This simulation is based on an integral formulation for the current vector potential T in the HTS tape, which geometry is simplified with a thin-strip approximation. Superconducting behavior is described through an E-J power-law relation with B-dependent critical current. Simulated systems can be tested under external B field or transport current.
Accuracy of the simulation is then assessed by comparison with our experimental measurement. We prepared a small insulated coil with 80 turns of 4 mm-wide YBaCuO tape provided by SuperOx. It was tested at 77 K, after injection and removal of transport current, the decay of the screening-current induced field was monitored for several days with high sensitivity Hall probes. Finally, simulation performances are also benchmarked against the Minimum Electro-Magnetic Entropy Production (MEMEP) code developed at the Slovak Academy of Sciences.
The present aim is to provide a user-friendly free and open-source screening-current simulation code for HTS tape-based systems that will benefit magnet designers on current and future projects.

A split-gap superconducting magnet with a center field of 8 T has been designed and fabricated. There are two BSCCO coils and six NbTi coils in the superconducting system. Due to the large aspect ratio of the high temperature superconducting tape, there will be a large ac loss while the magnet is ramping up and down. Accurate estimation of the total ac loss in the coil is essential in cryogenic system design. In the BSCCO coil, the total ac loss originates from two parts, one is transport loss caused by the transport current in the coil, and another is magnetization loss due to the external magnetic field generated by the NbTi superconducting magnet. In [1], it shows that there is temperature dependence for the transport loss and magnetization loss in the high temperature superconducting tapes. In this paper, we investigated temperature dependences of transport loss and magnetization loss in the BSCCO coil separately. In the calculation, we take the Jc dependency of each turn into consideration to improve the accuracy. The calculations are divided into four parts; firstly, we calculate the transport loss under different transport currents and temperatures. Secondly, we calculate the magnetization loss under different external magnetic fields and temperatures. Thirdly, we get the total ac loss when the BSCCO coil is charged into a transport current and exposed to an external magnetic field generated by the NbTi coils under different temperatures. Fourthly, we change the sequence of charging transport current and exposing to external magnetic field to get the total ac loss. The effects of the sequence of the transport current and external magnetic field on total ac loss in the coil are also discussed.

In general, the AC loss is lower when the operating current is small than when the one is large, at the same operating temperature. HTS coils could have wider range of the operating temperature than the low temperature superconducting (LTS) devices. The loss of the coil at the lower temperature with the same operating current is expected to be lower because of the higher critical current. But the temperature dependency is not so simple. In case of the short HTS tapes with the same size and different critical currents (Ic), the one with higher Ic has lower AC losses only below certain magnetic field. It is not known yet for the AC loss variations in the HTS coil at the various temperature with the same operating temperatures. We analyzed the temperature dependency of the loss of high temperature superconducting (HTS) coils.We have designed and tested several sample HTS coils to establish the design criterion based on the temperature dependency of the loss.

This research was supported by Korea Electric Power Corporation Research Institute through Korea Electrical Engineering & Science Research Institute. [grant number : R14XA02-23]

The problem of demagnetization in superconducting bulks in practical applications has received considerable attention in recent years. Yet the redistribution of the current inside a superconducting bulk because of the crossed and rotating magnetic field is the biggest objection on their practicability in rotating machines. Recently, the stacked-tape-configuration unveiled a great potential as an alternative to superconducting bulks. On the basis of the finite element analysis, a detailed assessment is carried out to ascertain how the physical geometry of a sample can not only enhance the initial magnetization, but also, more importantly, to lessen the demagnetization. It is proven that the trapped field is logarithmically proportional to the number of layers and its maximum trapped field occurs while the aspect ratio is around one (with non-magnetic substrate). In this regards, the magnetic substrate plays an important role as it decreases the leakage of the magnetic field that results in higher trapped fields. Furthermore, it is shown that the amount of demagnetization due to crossed or rotating magnetic field is greatly smaller in stacked tapes in comparison with HTS bulks. This feature of stacked tapes will work better with magnetic substrate as the high permeability of the substrate will prevent the field to enter to the substrate that results in smaller demagnetization. In addition to self-protective intrinsic nature of stacked tapes that is associated with the thick- ness of superconducting tapes, a state-of-the-art technique is introduced for further protection of tapes as opposed to crossed and rotating magnetic fields. This technique, which is based on the shielding characteristic of superconducting tape, becomes even more interesting when it is applied to superconducting bulks, where a striking reduction of the demagnetization is achieved.

Due to the rapid progress in the superconducting material fabrication technologies, several kinds of commercial 2G HTS coated conductors are available from the market. Since different manufacturers have different producing routines, the properties are quite different. So it is quite important to characterize and access the performance of superconducting coils with different tapes. This paper is devoted to study the critical current and ac loss of superconducting coils with SuperPower and SuNAM conductors in self field.
The experimental part firstly measure Ic in short tape sample with different external field direction. Then critical current and AC loss of two 20-turn superconducting coils are performed in liquid nitrogen. The simulation is done based on magnetic minimisation approach taking the superconducting layer as strip in cylindrical coordinate. The simulation process sovles the current density distribution, then the magnetic field is calculated using finite element method. After this, the critical current on each element is calculated combined with measured Jc with external magnetic curve. This is repeated until the current density distribution of the coil converges. The critical current of coil and ac loss is well estimated by our model. We also discuss the different anisotropy characteristics of coated conductors in critical current and AC loss estimation.

Abstract: The turn-to-turn direct contact of no-insulation (NI) coil will radially bypass the current from original superconducting winding layer at high charging/discharging rate or over-current testing, which results to the enhancement of coil electrical and thermal stabilities. The NI HTS coils therefore enable a high overall current density with compact size and protection-free design technology. However, in the case of AC current, the heat dissipation resulted from characteristic resistance of turn-to-turn contacts has made an additionally major contribution to the total AC losses. This part of loss needs to be quantified and carefully removed by the cryocooler. Unlike the frequency independence of the superconducting hysteresis loss, the turn-to-turn characteristic resistance is frequency dependant under the same coil winding tension due to the nature of the ohmic loss . In order to calculate the characteristic resistance, 30 turns single pancake coils with and without insulation were fabricated separately, the winding tension of the coils are carefully kept at constant value. AC loss measurements at various frequencies based on the electrical method were performed on the two coils and the variation of AC losses indicate the turn-to-turn characteristic resistance effect. The experimental results were compared with coil FEM modelling to validate the proposed characteristic resistance determination approach.

Key words: AC loss, FEM, no-insulation coil, turn-to-turn characteristic resistance

Because of the high current density and good mechanical performance in high magnetic field, there is much interest in fabricating high field magnet with 2G HTS tapes. While there are several newly commercialized coated conductors, it is quite important to characterize and access the performance of superconducting coils in external field. This paper is devoted to study the critical current and ac loss of superconducting coils with SuperPower and SuNAM conductors in external parallel fields.
The experimental part firstly measures Ic in short tape sample with different external field direction. Then critical current and AC loss of two 20-turn superconducting coils are performed in liquid nitrogen. The simulation is done based on magnetic minimisation approach taking the superconducting layer as strip in cylindrical coordinate.
The Ic measurements revealed that the field dependencies of SuNAM and SuperPower tapes in external magnetic field are quite different. While SuNAM tape has more Ic degradation in perpendicular field, the newly developed tape by SuperPower degrade more in parallel field. This results in considerable different behaviours in coils, especially taking the external field account.
Different field dependency expressions are inserted into the simulation models. Good agreements are found in Ic determination and AC loss measurement.

Cryogenic coolers have been widely used in superconducting devices for their advantages in easy maintenance and economical operations. The utilization of cryocoolers requires the impregnation of the superconducting tapes and coils to enhance the thermal and mechanical stability. This paper analyses ac loss and critical current of superconducting coil impregnation process experimentally.
Two coils are wound by insulted tapes from SuperPower and SuNAM. AC loss and critical current are characterized before insulted them with epoxy resin, Stycast Black and liquid metal GaInSn. After the winding with epoxy resin, the coil is vacuumed to vacuum degree of 1 mbar for 5 mins. Then the vacuum is released and the coil is cured in room temperature for 24 hours. After curing process, the AC loss and critical current are measured again in liquid nitrogen bath. This is repeated with several thermal cycles. The influence of impregnation process and thermal cycles are fully discussed.

MgB₂ coils are being developed in the Suprapower project for their use in wind turbine generators. MgB₂ conductors have a multifilamentary superconducting structure encased in sheaths of different materials. When working in magnetic field, conductors with ferromagnetic sheaths, such as Ni or Fe, distribute the magnetic field concentrating it in the magnetic material, while the non-magnetic materials does not cumulate the magnetic flux lines. The distribution of the magnetic field can affect the superconducting filaments performance, decreasing the critical current, I_c, of the coil, thus it is an important parameter to evaluate the load-line of coils.
When characterising the load-line of MgB₂ coils made with ferromagnetic sheaths the winding is considered as a bulk ferromagnetic material, without considering the internal magnetic field distribution. This assumption has shown lower I_c numerical predictions compared with the experimental results. Hence more representative modelling will lead to savings in cost and weight of the coil design.
In this work the full multifilamentary structure of Columbus tape, with 19 MgB₂ filaments, Ni outer matrix and Cu stabilizer is built using electromagnetic finite element modelling. As a first step the load-line results is verified against experimental data. Further to this the variation of the load-line with a wider set of µ values is explored. Detailed information about the magnetic field distribution inside the conductor and a clear identification of the filaments most affected by the magnetic field are presented. Subsequently the filament architecture is be optimized, and the load-line compared to the original conductor.

This work has been partially funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 308793

The study of AC losses is of utmost importance for power applications of high temperature superconductors, namely in components such as coils, as they must be removed by expensive cryogenic systems which can ultimately dictate the economic viability of these technologies. When considering applied currents with more than one harmonic component, the measurement of such losses becomes complex as common electromagnetic methods, where single frequency signals are required, cannot be considered. In this paper, a calorimetric method based on the measurement of evaporated nitrogen is implemented in order to measure losses in HTS coils carrying transport currents with multiple harmonics. Experimental data obtained using this method considering one harmonic is compared to that acquired using an electromagnetic method, for validation purposes. Results obtained considering more than one harmonic component are presented and discussed. Losses are measured in a HTS coil with 128 turns, implemented with BSCCO tape and considering harmonics at 50, 250 and 350 Hz (respectively power grid fundamental, 5th and 7th harmonics).

Nuno Amaro acknowledges Fundação para a Ciência e Tecnologia - MCTES for financial support through a PhD scholarship with the reference SFRH/BD/78418/2011

The continuous increase in demand for smart electrical distribution grids and related power systems operating in low, medium or high voltage networks has recently raised the world-wide interest on the development of efficient protection systems against short-circuits, such as superconducting fault current limiters (SFCL). Important parameters for assessing an SFCL are price, size, cooling, and weight, plus reliability. This paper concentrates on improving the reliability figures on the technical assessment of resistive type SFCL, from the physical point of view. The model described herein enable us to fully analyse both the current limiting characteristics of an SFCL before, under, after fault conditions, and importantly its detailed thermal behaviour. Being able to predict the instantaneous distribution of heat enables us to militate against the hot spot formation and cyclic degradation. For this purpose, here we introduce a sophisticated proprietary 3D electro-thermal computational package for multilayer structures, where the design and selection of materials is straightforward. The software operates on the basis of a fully 3D electrical-circuit model coupled to the Fourier Law for solving the heat transfer equation. In the case of SC materials, the anisotropy parameters related to the thermal and electrical physical properties along the ab-planes and c-axis are directly considered from experimental data. For the superconducting state, the conventional E-J power law as a function of the temperature has been considered, whilst for the normal state (or normal materials) the temperature dependent electrical resistivity is defined. On the other hand, the thermodynamic properties of the materials involved have been included through the temperature dependence of the thermal conductivity (anisotropic for SCs) and their heat capacity. Finally, it is worth mentioning that different cooling conditions can also be included. In particular, the boil-off properties for LN2 have been incorporated by a weighted least squares fit to a large amount of experimental results reported into the literature.

This work was supported by the UK-EPSRC under Grant NMZF/064

Superconducting fault current limiters (SFCL) are expected to withstand inrush currents without quenching. Since inrush currents are relatively slow, heterogeneous quenching may take place, leading to the formation of hot-spots. In this work, the FDM-ADI method has been employed to investigate the quench process in resistive SFCL devices under inrush conditions. We have recently reported on the use of finite difference method (FDM) combined with the alternating direction implicit (ADI) routine to simulate superconducting fault current limiters devices (SFCL). This method has been shown to be an alternative approach due to the possibility of including inhomogeneities regarding critical current values as well as values of the index of transition n. Furthermore, the FDM-ADI method can provide relatively fast algorithms, since the simulation time is lower than that of traditional methods. The tested devices are a MCP-BSCCO-2212 module and an YBCO 2G coil. Each SFCL was submitted to current levels up to 2-3 times the normal operating current for a few seconds. Experimental results were compared with simulations. Both devices showed an optimum inrush behavior under the testing conditions.

 Due to the large stored energy and the small allowed number of fast discharges, severe requirements have been put for the Toroidal Field (TF) system in comparison with the Poloidal Field (PF) and Central Solenoid (CS) systems, aiming at avoiding fast discharges not related to a quench. The TF quench detection system is complicated due to the direct strong coupling with huge plasma current and eddy current .Even minor disruption and ELMs may cause inductive voltage on the TF coils and it is essential that it is not permitted to generate false quench detection signals after a plasma event, or to selectively weaken the detection criteria which would result in a risk of permanent damage of the magnet in case of real case.Several false fast discharges of TF coils had been generated by using traditional voltage detection method in the past EAST runs. 
   Due to fast the normal zone propagation velocity (NZP)of LTS quench,detecting voltage shall be increased along one direction very sharply in case of real events which is completely different with residual noise voltage.
  Compared with detection voltage , the unidirectional voltage change rate as discriminant criterion should be more fast response and stronger anti-interference ability.The feasibility study 
have been carried out through a simulation platform and a real ,superconducting  Running Tokamak System in advance.The latest experimental results on EAST showed that the upgraded quench detection system of TF coils has met the requirements of experiments.
 

The work described is the work of EAST quench detection team.

Stability is one of the most important aspects in design of superconducting conductor which determine the reliability of magnet, and deserves much attention in magnetic application. Although the stability experiment is regard as the most reliable approach, modeling of CICC is available for its advantage in efficiency and performed well in optimizing CICC in magnetic system.
This paper is aim to introduce a finite element method with ANSYS to deal with the integrated analysis of thermal, electrical and fluid model of CICC. This model is based on typical CICC with cooling channel. It is cooling by supercritical helium.1D element types of thermal and fluid are used to represent CICC components of strands and two separated fluid area of bundle and central hole respectively. Temperature of these three components is treated separately. Electrical distribution in conductor strands which related to heat generation rate is as function of temperature, current density and magnetic field. The friction factor of the two fluid areas which used to determine the flow mass division has also been discussed.
This method is supposed to simulate quench triggering and quench propagation in CICC’s. It is a feasible way to estimate stability performance under operating condition, and giving access to all parameters and detail during thermal runaway or quench-recovery process. The stability evaluation of CICC of China Fusion Engineering Test Reactor (CFETR) central solenoid model coil with this method is also concerned.

Thanks for all the colleagues' contribution for CFETR CS model coil in ASIPP.

No-Insulation (NI) winding technique to REBCO pancake coils has been received attention. This technique is expected to improve the dynamic thermal stability and increase the overall current density. Since the turns of NI REBCO pancake coils electrically is used NI REBCO tapecontact each other on the large flat surface, the transport current can bypass and flow into adjacent turns to prevent from flowing to a local hotspot. Therefore, the bypass current makes the coil stability high. The NI REBCO pancake coil is characterized by Between turns of an NI REBCO pancake coil are indicated as the contact resistivity between turns. Here, an NI REBCO tape commonly consists of a superconducting (REBCO) layer, a (Hastelloy) substrate (Hastelloy) layer, a copper (or silver) stabilizer, and so on. When the transport current flows into the adjacent turn, the transport currentit cannot flows through the stabilizer at the both sides of REBCO tape to the superconducting layer of the next turn, escaping into from the Hastelloy substrate withlayer because of its high resistivity, and flow to the REBCO layer of the adjacent turn through the copper stabilizer at the both edges of REBCO tape. Therefore, the thickness of copper stabilizer at the both sideedges of REBCO tape is an important factor as well as the contact resistivity. Hence, it is important necessary to investigate the electrical behavior of the current flow to adjacent turns by the thickness of copper stabilizer. It also affects the thermal stability of NI REBCO pancake coil. Since it is difficult to investigate the behavior inside an NI REBCO pancake coil by experiment, it is necessary to use a numerical simulation to investigate the influence of the thickness of copper stabilizer on the bypass current to adjacent turnssimulate it.
In this paperstudy, an NI REBCO pancake coil is simulated to investigate the electrical transient behavior. In the simulation of an NI REBCO pancake coil, a two-dimensional finite element method (2-D FEM) is used as the electrical simulation method. Through the simulation using the 2-D FEM, we investigate the electrical behavior in the rectangular cross section of REBCO tape, and will reveal the influence of the copper stabilizer thickness on the bypass current to adjacent turns.

Liquid hydrogen has excellent properties such as large latent heat, low viscosity and so on. Because of these properties, liquid hydrogen is expected to be used as a coolant for high critical temperature superconductor (HTS), including MgB₂. Over current properties of HTS are important for stable designs of HTS devices cooled by Liquid hydrogen, but temperature change of sheathed superconducting wire cannot be revealed only by current-voltage properties beyond critical current.
In this study, temperature change of Cu-sheathed MgB₂ wire cooled by Liquid hydrogen was obtained by applying electric current to give transitional heat input. In addition, validity of the obtained temperature was discussed by numerical analysis. It was found that the temperature transition while transport current exceeds critical current is affected by external magnetic fields and degree of subcooling.

Thermosyphon refers to a method of heat exchange based on natural convection circulating a fluid without the requirement of a mechanical pump. Thermosyphon cooling is used for circulation of liquids and volatile gases in cooling for HTS machine systems. The cooling system was focused on the temperature range of 25 K to 40 K, currently suitable for applying HTS machine systems. The system is composed of condenser, evaporator and adiabatic tubes. A heat transfer capacity is decided by each component performance. We have conducted a study of guiding and behavior of liquefied refrigerant under gas-liquid two phase system with effect of diameter of the adiabatic tube in the heat transfer system for HTS machine　systems. In the course of this work, we study survivability of a model of 100 W grade systems by using neon-gas condensation and circulation with respect to unsteady heat load, transient heat conduction problem with transient thermal stress. We report the effect of the diameter of adiabatic tube on the heat transport and discuss the result of the heat load test with applying adiabatic tube of different inner diameter and the limit of heat transfer capacity.
Ref.: Brice Felder, Motohiro Miki,Keita Tsuzuki, Nobuyuki Shinohara, Hironao Hayakawa and Mitsuru Izumi, A 100-W grade closed-cycle thermosyphon cooling system used in HTS rotating machines, AIP Conf. Proc. 1434, 417 (2012); 13–17 June 2011, Spokane, Washington, USA.

AMIT cyclotron is a compact device aimed to produce radioisotopes (mainly carbon-11) for medical imaging. A uniform 4T field is created by means of two NbTi coils in a Helmholtz arrangement. Both coils are embedded in a stainless steel casing which hold the Lorentz forces. The refrigeration scheme is based on a low pressure forced internal flow of biphase liquid-vapour helium through a winding narrow channel machined in the casing. Preliminary thermohydraulic analysis showed that this concept is capable of cooling the coils and taking a heat load of 1W with just an small amount of mass flow (about 0.1 g/s). These numbers matches the specifications coming from the custom re-liquefaction closed-circuit system (CSS). The CSS is powered by just one cryocooler to minimize the cryogenicscosts. This paper will present the results of a scaled mock-up of the magnet, cooled by such a kind of helium flow, tested to check the thermal loads, quench training, fluid-solid interaction and the necessary control system to handle the Helium mass flow. It will prove the viability of the concept while advising the potential problems that could arise in the real system.

This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project reference CEN-20101014.

In the frame of the SUPRAPOWER Project, MgB2 conduction-cooled coils are used in the rotor of synchronous wind turbine generators as induction field DC coils with working temperature of around 20 K. As a result, a conceptual design of a 10 MW superconducting generator will be made and a Rotating Magnetic Validator (RMV) will be constructed and tested, with two rotating superconducting coils, keeping the same winding dimensions. The main working conditions of the 10 MW generator, as superconducting coil operating current, temperature, magnetic field, cryogen free cooling system and rotating conditions will be kept. The RMV has been conceived is such a way that it can be transformed easily in an electric generator with some additional components (mainly two more superconducting coils with their corresponding modular cryostat and armature winding). Numerical quench simulations have to be performed in order to design a suitable protection system to ensure that this event will not damage the coils of the RMV and the machine. Due to the uncertainty of some material properties and its importance for the machine operation, an experimental validation must be performed in order to resolve discrepancies. Under this premises, the MgB2 DC field coils have been designed, manufactured and instrumented to trigger a controlled quench and to register the evolution of the main magnitudes during this event. This paper describes the models developed to perform the simulations and obtained results are discussed.

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 308793.

The magnetization of layered high-temperature superconductors was studied by using Monte Carlo method. The magnetization curves for typical parameters of ReBCO, BSCCO, MgB2 and iron-based superconductors were calculated, the effect of anisotropy on the magnetization and transport properties was analyzed. The vortex configurations arising during magnetization were obtained. The ferromagnetic nanorods of arbitrary radius and constant magnetization were considered as bulk pinning centers, the effect of extended ferromagnetic defects of arbitrary shape was also analyzed. The magnetic part of the interaction energy between a ferromagnetic cylinder and an Abrikosov vortex was calculated in London approximation. The calculations were done for both ferromagnetic and nonmagnetic extended defects.

Research was done with the financial support of RSF under grant № 14-22-00098

The scope of this article is to compare transient responses of 2G HTS tapes under alternating overcurrent. The authors performed the series of measurements of the SF4050 and SCS4050 HTS tapes produced by Superpower Co. The measurements were carried out for various amplitudes of current exceeding critical value given by manufacturer (Ic=100 A, DC, @77 K, self-field). Seven measuring probes were soldered to the each tape, which allow for simultaneous recording of the supplying current and voltages in each test segment. Tapes were immersed in liquid nitrogen bath under atmospheric pressure and supplied from the 50 Hz voltage source with adjustable amplitude.
The specific heat values of the tapes were measured using differential scanning calorimeter (DSC PYRIS Diamond, Perkin Elmer, USA) in the temperature range 100 K-523 K. Obtained characteristics allow to determine the instantaneous tape temperatures during overcurrent transients.
Numerical models of SF4050 and SCS4050 tapes were build using PSPICE environment. The models assume the nonlinear dependence of tape parameters in the function of temperature and the variable cooling conditions during transient state. The numerical results were compared with the measurements and good correlation was achieved. Elaborated models allow for calculation of the overcurrent responses of 2G HTS tapes and tapes with copper shunts.

Permanent magnets have been the magnetic materials forming the excitation system of electromechanical converters. However, with the emergence of high-temperature superconductors, it has been open the possibility of trapping higher magnetic fields. From about 1.4T in NdFeBs, bulk superconductors can trap fields near 2T at 77K using liquid nitrogen. Also, new means of multiphysics analysis and simulation is making possible the study, analysis and design of converters with bulk HTS materials inserted into their magnetic circuit.

In that context, synchronous generators using HTS magnets, particularly low-speed ones for renewable sources of energy, can become extremely attractive. Increasing their magnetization level, lighter (less iron or air-core) and higher power density are expected milestones.

This paper presents the first results to characterize the coupled electromagnetic-thermal behavior of YBCO superconductors to verify the ability to maintain not only its superconducting state but also its level of magnetization when subjected to a time-variant magnetic field (variant amplitude and frequency) when inserted in a low-speed generator.
A Comsol electromagnetic-thermal coupled model of the YBCO allowed us not only the computation of its circulating currents and excessive power dissipated by Joule and hysteresis effects, but also computation of temperature rise in the YBCO, losing or not its superconductivity in certain YBCO spots.
The YBCO behavior in a FC (Field-Cooled) mode and when in magnetic field confinement, ,point out the advantages and disadvantages of this solution for the realization of excitation systems for low-speed generators. Experimental results show that the magnetization is lost more rapidly for higher magnetic fields (the frequency remaining at 50 Hz) in about 15 min, as previewed by the FEM model. This time gives the first indication concerning the YBCO magnets fiability when, for example, a three-phase short circuit happens in the generator.

The analysis of the magnetization process of superconducting tapes has a relevant role to improve the performance of superconductor devices such as motors and electrical generators. Modeling this process permits to determine the behavior of the stack.

Modelization of one superconducting stack with few tapes has several approximations. In this work we show the results of 2D model of a 20 mm long stack composed by ten tapes and we determine the profile of trapped magnetic field.

The model shows the results of magnetization process when the magnetic field applied is: (i) homogeneous sinusoidal magnetic field, (ii) the field produced by a sequence of permanent magnets with inverted poles.

In case (i), after magnetization process is finished, we studied the behavior of the stack when a transient magnetic field is applied for a full period.


The research leading to these results has received funding from EU-FP7 NMP-LA-2012-280432 EUROTAPES project, MAT2011-28874-C02 national project.

Performing a quench propagation simulation of full size superconducting coils is a challenging problem due to complex coil structures and internal arrangement of superconducting wires. In addition superconducting wires and cables themselves may have complex 3D arrangements comprising of superconductor, matrix, stabilizer, insulation and other materials. Modelling quenches in complete coils is therefore a complex multi-scale and multi-physics problem that is difficult to solve with conventional techniques like finite element or finite difference methods. Monte Carlo methods have been successfully used to simulate various multi-scale and multi-physics problems, but to our knowledge have not been exploited for quench propagation simulations. In the presented work the application of the Monte Carlo method for quench propagation problems has been studied and first results are presented. A mesh free Monte Carlo method has been used that lends easily to parallelization. Quench simulation for a simple case of short straight superconductor wire using the Monte Carlo method has been performed and compared with other methods.

Authors would like to acknowledge the support extended by IIT Kharagpur, India.

With the development of large superconducting generators based on MgB2 conductors, the question of protection against electrothermal instabilities in both the stator and rotor needs to be addressed. The stator conductors, in addition to having fine filaments and a short twist pitch to limit the AC losses needs to present a high resistivity matrix material. Interupting the current in the stator is not an issue since the current naturally has a zero value twice a cycle. The rotor conductor's requirements are different aiming more towards increased stability since quench protection relies on the discharged of the stored energy limited by the rotor winding inductance. The stator conductor will likely be based on a CuNi matrix while the rotor conductor will mostly use Cu. Understanding the impact of the matrix material on quench propagation is paramount to design an effective detection system. This paper will present numerical analysis of quench propagation in the stator and rotor winding of a fully superconducting machine. The dtat generated can be used as guideline for the design of fully superconducting machines. Detection and protection will also be discussed for both the rotor and stator.

Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) is responsible for the design, construction and test of 8 pair of 6 kA and 7 pair of 12 kA high temperature superconductor (HTS) current leads for the NICA accelerator magnet at the Joint Institute for Nuclear Research (JINR) since 2012. The 6 kA current leads are of the binary type, the HTS part covering the temperature range between 4.5 K and 77 K while the heat exchanger covers the range between 77 K and room temperature being cooled by liquid nitrogen, and the current leads are required with a nominal current of 6 kA and a maximum current of 8 kA. This paper describes the test setup and test results of 6 kA HTS current leads.

High temperature superconducting (HTS) bulk materials of RE-Ba-Cu-O (RE: Y or rare earth elements) called “QMG”, developed by Nippon Steel & Sumitomo Metal Corporation, are an ideal material for current lead applications, and QMG current leads have been successfully utilized in many practical systems. It is well-known that melt-processed HTS bulk materials exhibit excellent J_c-B properties even at 77 K, leading to large current capacity and superior magnetic field tolerance. In addition to the fact that the thermal conductivity of HTS bulks is two orders of magnitude smaller than that of the conventional current lead material of copper, Dy-Ba-Cu-O is employed in QMG current leads because of its lower thermal conductivity in the family of RE-Ba-Cu-O. Different from HTS wires, HTS bulks have no metal sheath such as silver or silver alloys with high thermal conductivity, resulting in the reduction of heat leak through the current lead even in the compact size. Although RE-Ba-Cu-O may be a kind of brittle ceramics or oxides, they can be reinforced by combing with the support cover made of glass fiber reinforced plastics (GFRP) with low thermal conductivity and high strength. The rigid GFRP reinforcement double-fastened by epoxy resin bond and stainless steel bolts improves the mechanical properties of QMG current leads with the total heat leak kept low. Furthermore, QMG current leads are robust not only for external mechanical stress but also for thermal stress, which was experimentally demonstrated in the thermal cycle test where the rapid cooling from room temperature to the liquid nitrogen temperature of 77 K was repeated over 100 times. Thanks to distinctive advantages such as compact, robust and superior field tolerant, QMG current leads have made it much easier to design superconducting coil magnets cooled by refrigerator without cryogen such as liquid helium. HTS bulk current leads are expected to more and more contribute to developing and spreading the cryogen-free magnets.

A new cryogenic DC superconducting current transformer (CryoDCCT) has been developed and fully commissioned at the Facility for Research on Superconducting Cable (FReSCa) at CERN. The device has been designed to provide current measurements with accuracy of the order of 10 ppm for a rated current of 100 kA at an operating temperature of 4.2 K. In a previous work, the authors reported on the effectiveness of the device through metrological characterization at 80 kA. However, the CryoDCCT was mainly conceived to be exploited as current transducer for the secondary current of a superconducting transformer used to test superconducting cables. In this full paper, the commissioning of the CryoDCCT is reported, once installed in a purpose-developed cryogenic insert housing a 70 kA superconducting transformer in the FReSCa test station. The performance of the CryoDCCT was demonstrated through the characterization of a Nb3Sn sample cable using the aforementioned superconducting transformer insert.

The authors thank C. Berriaud at CEA Saclay for sharing his expertise. The authors also thank M. Cerqueira Bastos, Greg Hudson, and M. Martino for the fruitful discussions and useful suggestions. The authors are grateful to Hitec for allowing intellectual property material to be used.

CRPP hosts two unique conductor test facilities SULTAN and EDIPO, which allow the test of high current superconductors in high magnetic fields (SULTAN 11 T, EDIPO 12.5 T). Sample currents up to 100 kA are supplied by means of a NbTi transformer. For the test of high current HTS conductor samples at temperatures between 20 and 50 K, an HTS adapter and counter flow heat exchanger have been manufactured. The HTS adapter, each leg made of 75 RE-123 coated conductors of 12 mm width, reduces the heat flux between the HTS sample under test and the NbTi transformer to less than 5 W per leg at an HTS sample temperature of 50 K. A tube-in-tube counter flow heat exchanger supplies 4-10 g/s of helium gas with a temperature of 20-50 K. The warm helium leaving the HTS sample under test is in counter flow with helium of 4.5 K and a pressure of 10 bar supplied by the cryoplant. The inlet temperature to the HTS sample under test is adjusted with a heater. The commissioning of the HTS adapter and the heat exchanger is combined with the test of a 60 kA HTS prototype sample assembled at CRPP. Important aspects addressed by the commissioning are the joint resistances (NbTi transformer – HTS adapter, HTS adapter – HTS sample), the current carrying capacity of the HTS adapter and the relations between helium mass flow rate, heater power and helium inlet temperature.

Electrical Quality Assurance (ELQA) of the superconducting electrical circuits in the LHC requires an advanced test equipment accompanied by the specialised software, data storage system and analysis toolset.
In 2007 the measurement system was built in order to carry out the Test Procedure 4 (TP4), namely the qualification of the complete superconducting circuits in terms of instrumentation routing, insulation quality and other electrical parameters. This measurement system has become the main ELQA tool at the LHC.
During the testing campaign at LHC in 2007-2009 a set of new functionalities was proposed. For the Long Shutdown 1 of the LHC (2013-2015) the number of the measurement systems had to be increased from existing four to eight units. In view of these facts in 2010 the decision was made to perform the upgrade of the TP4 system.
In this paper we describe the requirements, the upgrade process which was carried out in the Institute of Nuclear Physics Polish Academy of Sciences in Krakow, the architecture and parameters of the upgraded system, including the maintainability improvements. We also present examples of the automated electrical tests of the LHC superconducting circuits performed with the upgraded TP4 system which show very high flexibility and extendability of the implemented solution.

The authors thank Andrzej Kotarba from IFJ-PAN, Krakow, Poland and Mateusz Bednarek from CERN, Geneva, Switzerland for participation in the design of the initial version of the described measurement system and valuable consultations during the upgrade process.

To make practical use of the high-temperature superconducting(HTS) magnets, it is important to detect a sign of failures by the temperature monitoring. Because quench protection of HTS magnets is difficult. HTS magnets has temperature distribution when it is cooled by conduction cooling. Therefore, reliable multipoint temperature monitoring method is necessary.
Unlike the conventional resistance temperature sensor, the optical temperature sensor can measure multipoint temperatures with a single fiber. The optical fiber is not affected by the fluctuation of magnetic field and has low heat invasions.
A Fiber Bragg Grating (FBG) is a type of the optical fiber temperature sensor. When the FBG sensor thermally contracts, the refractive index of it changes and the wavelength of the light reflected from it changes. The thermal expansion rate of an optical fiber decreases at cryogenic temperature. Therefore, the accuracy of the measurement also decreases. It has been proposed to coat the FBG sensor with a metal or a resin to increase thermal contraction at cryogenic temperature.
Zinc is suitable for the coating material, because it has high thermal expansion rate and its coating process is simple. Three types of zinc coating methods were evaluated in this research: sputtering, electroplating after sputtering titanium and copper, electroplating after electroless nickel plating. The production cost of these methods were evaluated. These zinc-coated FBG sensors were compared in the sensitivity at cryogenic temperature, the durability against vibration and thermal shock, the repeatability during the cooling cycle.
We report the evaluation results of the zinc coating method on the optical fibers as a cryogenic temperature sensor.

This work was financially supported by the Japanese Ministry of Land, Infrastructure, Transport and Tourism.

Measurement of the AC magnetization loss is a standard and often used method to characterize the superconducting samples such as tapes, wires and cables. One of the methods suitable for this type of measurement is a calibration free method. The original measurement setup consists of two identical AC coils connected in series. A substantial part of the method is the measurement coil wound in parallel with the first AC coil and the compensation coil wound in parallel with the second AC coil. The measurement coil and the compensation coil are connected in opposite in order to compensate the measured signal. The sample is located inside the AC coil with the measurement coil, and the signal is measured by the lock-in technique. In the modified method we propose only one AC coil, in particular that one with the measurement coil. The measured signal is now compensated with a new compensation coil which is located inside the AC coil together with the sample in such a way that they do not influence each other. The modified method results in decrease of costs for both the construction of AC coil (now we have only one coil) and the coolant. Simultaneously the requirements on the AC power supply are lower because of the lower self-inductance and resistivity of the AC coil. The other option is to design the AC coil which either enables to measure longer samples or generates higher magnetic field. Such a modified apparatus was designed, constructed and tested. The AC coil is made with copper cable (1+6+12 strands) and cooled by liquid nitrogen. The specific feature of the AC coil winding is the utilization of the cooling channels between individual layers. This allows us to operate the coil with higher current than corresponds to the case of compact winding, generating the magnetic field up to 200 mT. The magnetization loss of the BSCCO sample was measured using the modified calibration free method and compared with the results obtained by the original calibration free method.

The definition of the magnetic field quality is important part for the accelerator magnets production. The quadrupole magnets which are situated in the accelerator beam line have to be characterized with respect to magnetic axis stability and higher field error. This can be done with a rotating coil method by using high precision equipment. The paper presents a rotating coil setup which provides synchronized measurements of the magnetic field stability and harmonic analyses at the different currents as well as higher order field error. The mathematical processing is also presented in this paper. The described rotating coils setup was used for the acceptance tests of the XFEL quadrupoles magnets.

We are desiging a new separating device and among several other components we had designed vapour-cooled current leads. This current leads are based on a classical design (for proper stability and robustness of the full device that does not allow many degrees of freedom) and therefore made of Low-Tc material connected with copper wires and some parts of High-Tc material. Its design is calculated keeping in mind the heat transfer by diffusion to a vapour-cooled stream that surrounds the conductive materials. We have also designed forced-flow cooled current leads, for comparision purposes. The actual current lead heat influx is best determined in the vapor cooled mode.
The design and the calculations performed, and also the background theory of the heat diffusion applied in this part of the device will be described.

The Magnet Test Facility (MTF) at LBNL belongs to the Superconducting Magnet Group, and serves a core mission of testing performance characteristics of high field superconducting accelerator magnets. Several magnet parameters, such as maximum quench current, training behavior, and field quality are tested and characterized at the MTF. The facility is currently being upgraded to expand the magnet characterization range. Three key new systems are going through a series of tests: the High Current Power Supply (HCPS), the Energy Extraction System (EES), and the Quench Detection System (QDS).
The new power supply built by Alpha Scientific with the maximum operating current of 25 kA and voltage of 20 V was designed specifically to satisfy requirement of superconducting magnet testing such as uniform current ramping at different rates, as well as withstand magnet quench conditions. The output current regulation is better than +/- 0.04% of full scale over the full range of operation from DC to 1 MHz.
As a magnet quenches, its resistance grows via quench propagation and the internal temperatures as well as the voltage in the coils increase rapidly. To protect the magnet from thermal and voltage induced damage, a prompt detection of the developing quench and subsequent energy extraction should be accomplished. The new EES provides real time FPGA-based quench detection, and is very flexible and adjustable for a broad range of magnet testing scenarios. Quench condition is detected either by monitoring the differential voltage (imbalance) between the two halves of the magnet, or by detecting an excessive differential voltage (over-voltage) between the ends of any magnet part. Several other magnet conditions can potentially trigger the QDS and will be discussed.
Once quench is detected, power supply is shut down and the energy of the magnet is extracted by the EES. The key components of the EES are the configurable dump resistor, and the high current capacity silicon-controlled rectifiers (SCRs) that are responsible for commutating the current flow from the magnet through the dump resistor.
An overview of the new facility focusing on the three above mentioned systems as well as operational experience from the first magnet test will be presented.

The authors would like to thank J. Galvin, R. Albright and T. Lipton for their dedication and support in operating the magnet test facility.

Due to the high capability of energy transport, superconducting materials are rising as a good option for the development of electrical devices, such as cables, transformers, electrical machines and fault current limiters. One of the most promising superconducting materials is the second generation (2G) high temperature superconductor (HTS) tape. The 2G tapes have been successfully tested in order to replace conventional conductors in electrical device windings. However, it is well known that every superconducting material loses its superconducting state, if one of its critical parameters, which are the current density, temperature and magnetic field, is exceeded. As these critical parameters are related to each other, a magnetic field could lead to a reduction on the critical current of a superconducting material. In this context, this work aims to study the self magnetic field influence on the electrical characteristic of a 2G double pancake coil with different topologies using ferromagnetic material, where the field is created by the current on the device. The coil topologies are defined through 2D and 3D finite element simulations, in order to minimize the magnetic field crossing the 2G tape, and their IxV characteristic is measured. The results show that an optimal design could contribute to reduce self field influence on the IxV characteristic improving the performance of HTS equipment.

Bulk (RE)Ba₂Cu₃O₇ materials (where RE denotes a rare earth element) have exceptional magnetic flux trapping ability and represent a competing technology for powerful permanent magnets at 77 K. Well established contactless characterization techniques for large bulk superconductors (e.g. Hall probe mapping, magnetoscan) are primarily sensitive to the supercurrent distribution near the surface. If volume properties are required, classical magnetometers (e.g. SQUID, VSM) can be used. Such measurements techniques, however, are destructive since commercial devices usually accommodate relatively small size samples that need cut out from the original bulk pellet.

In the present work, we report measurements on whole bulk large grain GdBa₂Cu₃O₇ superconductors (up to 15 mm in diameter) using a recently designed bespoke magnetometer that can be used to measure magnetic moments as large as 1 Am² (1000 emu) on samples up to 20 mm diameter at 77 K. The magnetometer is based on a scale-up of the flux extraction technique. Its measurement range extends significantly that of commercially available devices. Both pick-up coil dimensions and integration bounds of the measured signal are optimized so that the device is able to extract the dipole magnetic moment of the sample, while being insensitive to moments of larger order within user-defined confidence bounds. The device is shown to be able to record the time dependence of the trapped magnetic moment of the whole bulk superconductors. In the present study, two significant applications are highlighted. First we study the influence of the magnetization process (FC, ZFC) and show that the magnetometer is able to quantify the significant increase of the magnetic relaxation rate when the superconductor is not fully magnetized. Second we show that the device is convenient to measure the trapped flux enhancement caused by a soft ferromagnetic disk attached to the bulk sample.

We thank the Communaute Française de Belgique for cryofluid, and equipment grants, under reference ARC
11/16-03.

In this paper, the peak current limiting characteristics of the superconducting fault current limiter (SFCLs) using dual iron core were compared to each other. Two magnetically coupled SFCLs connected in parallel or series between two coils. The peak current limiting and the recovery characteristics of these SFCLs can be varied depending on design conductions such as the winding direction and the inductance ratio between two coils. Through the fault current limiting and the recovery experiment, the peak current limiting effect and the recovery characteristics for these SFCLs were definitely explained.

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2013R1A1A2004916).

In this paper, we proposed a series connection-type superconducting fault current limiter (SFCL) that can prevent the internal magnetic flux generation of cores during normal operation, and prevent the saturation of cores due to a sudden magnetic flux generation at the initial stage of fault occurrence while limiting the peak current. The proposed SFCL does not mediate two cores, as reported previously, but mediates a single E-I core having a configuration of two magnetically coupled circuits using the first, second, and the third windings. The other magnetic path is formed by third coil and the other superconducting element isolated from two coils. Through a short-circuit experiment, we analyzed the operating status of the two superconducting elements and peak current limiting properties according to the amplitude of the fault current before and after the failure. Further, the peak current limiting characteristics according to the winding directions as well as the current and the voltage of each coil were compared and analyzed.

This work was supported by the research grant of the Kongju National University in 2014.

I would like to thank Prof. Yasuyuki Shirai and Prof. Jumpei Baba for their warm guidance and gentlemanly support. I would also like to appreciate Mr. Naoki Yonemura and Miss. Mariko Mukai for their valuable advice and important support in experiments.

The REBCO coated conductor (cc) tapes show great improvement in the critical current when compared with the YBCO cc tapes. Because of the critical current improvement on the REBCO cc tapes it became the most attractive properties for Superconducting Fault Current Limiter (SFCL) applications. Nevertheless in spite of these process evolution on the Ic and n-index values the effect of inhomogeneity on long tape lengths must be investigated in particular for resistive-type SFCL application where several hundred meters must be used for 15 kV voltage level units. The degradation or irreversible damage in REBCO tapes, assisted by an optimized external shunt resistor was investigated on 12 mm-width tapes. The modular unit with 6 stacks of 0.7 m-length tapes was built and tested by applying repetitive overcurrent during 80ms, with recovery time interval of 1 s (under load and no-load conditions), for prospective current level from 0.8 to 3 kA, with the rated current of Ir(rms) = 0.8*Ic. The electro-thermal model to simulate the REBCO cc tapes transition and recovery process was used for comparison with experimental results of the current limiting performance of a resistive SFCL.

The dc coil, ac coil, and the iron core are key components for a saturated iron core superconducting fault current limiter, determining the device performance in fault current limiting as well as in normal power transmission. They are also have great impact on the size, weight, and manufacture cost of the device, which are considerable factors influencing the utility's acceptance for the device. We have intensively investigated how the design parameters of the dc coil, ac coil, and the iron core are co-related and how they affect the functional characteristic of a saturated iron core superconducting fault current limiter. The investigations include theoretical analysis, computer simulation, and experiments. Design methods to optimize the performances and to minimize the size, weight, and manufacture cost were developed. These work and methods will be presented in this paper.

This work was supported in part by the National High-tech R&D Program (863 Program) under Grant 2015AA0501954.

Due to the field-dependent anisotropy, high perpendicular field located at two ends in a superconducting reactor winding leads to low critical current and high AC loss, while a superconducting non-inductive winding has nearly zero field to enhance its fault-current-limiting effect. This paper introduces a superconducting air-core power reactor (SACPR) having a series-connected non-inductive coil insert. The SACPR has a fixed inductance from the reactor unit and an adjustable resistance from the insert unit. It can be used as a smoothing reactor with nearly zero-loss, while it can also be served as a resistive-type fault current limiter when a power system fault occurs.

For the reactor design, 200A Type-HT DI-BSCCO tapes are adopted to wind a long solenoidal winding and two compensation windings located at two ends. The numbers of axial layer and radial turn are 34 and 12. The inner, outer diameter and height of the long winding are 180mm, 189.6mm and 219mm. The gap between the adjacent layers in the long winding is 2mm. Each compensation winding has 3 single-pancake coil units, with optimal adjacent gaps of 3.3mm, 4.3mm and 5.3mm inserted.

For the coil insert design, 50A Type-ACT DI-BSCCO tapes are adopted to wind a bifilar winding. Two insulated tapes having the same length are soldered in one tape terminal, and then wound in parallel into a non-inductive solenoidal coil. The non-inductive coil is inserted into the inner cavity of the reactor to obtain a background field.

With a FEM model, the critical current of the prototype reactor increases from about 67.9A to 97.7A with the two compensation windings having optimal gaps, and the AC loss is only 0.02W for 73A current. The background field for the non-inductive coil unit is 0.105T, and thus its voltage drop is 0.497V/m. However if the non-inductive coil is operated as an independent unit, its voltage drop is only 0.224V/m.

Conclusions can be made as follows: i) As compared to a traditional copper iron-core reactor or a superconducting iron-core reactor, the total reactor volume and operational loss of the SACPR are reduced to about 1-5%. ii) As compared to an independent non-inductive coil unit, the fault-current-limiting capability of the designed unit having a background field is increased to twice or above. iii) The SACPR can be tailored to suit various DC/AC power applications.

After the fault current limiting operation, the SFCL must be recovered to the superconducting state within a proper time according to a relay operation scheme in a power system. The recovery time defined as the time during which the superconducting component recovers to its initial condition after the current limiting operation, is very important to design an SFCL because the repetitive faults may occur in a real power system.
In the current limiting operation of the resistive type SFCL, the heat generation period is rather short (a few hundred ms), but the peak value of generating heat may be too large to be cooled in the nucleate boiling region of LN2. That means the heat flux at the superconductor surface easily exceeds the critical heat flux and heat transfer phenomena shifts to the film boiling region. Moreover, it was reported that the direct transition phenomena from non-boiling regime to film boiling regime is observed in the transient heat transfer in the pool of liquid nitrogen depending on the surface conditions of the superconductor.
Because the recovery time becomes long due to the low heat transfer coefficient of film boiling regime, it is important to promote the nucleate boiling, to prevent the stable vapor film and to back to the nucleate boiling regime as soon as possible after the fault clear.
Heat transfer property between heated metal and LN2 depends on the surface condition of the metal. In addition to increasing the cooling surface area, it is expected that the fins promote the nucleate boiling and prevent from quick jump to film boiling regime. Teflon coating is also expected to promote the nucleate boiling and to make vapor film unstable.
In this paper, the cooling properties of YBCO tape with fins or with Teflon coating are investigated. Superconducting tape was heated by current, which is larger than its critical current and then shut down, in liquid nitrogen.
The cooling down speed after the current shut down back to the superconducting state was investigated. To clarify the effect of the surface conditions on the heat transfer characteristics, the superconducting test tapes with various shaped fins or with Teflon coating were compared with that without any fins or coating. It was confirmed experimentally that the recovery time is improved both with fins and with Teflon coating.

In this paper, a 220V resistive superconducting fault current limiter (SFCL) prototype is built and tested under different prospective fault currents, which vary from 0.8kA to 7.4kA. A 2D superconductor model is integrated into an experimental circuit model in COMSOL to simulate the performance of the SFCL prototype in the experimental system in fault tests. In the simulation, a new E-J relationship is proposed to enhance the convergence of calculation. Comparison between simulation results and experimental results shows that the proposed model performs well in simulating current limiting performance of SFCL in experimental system in case of fault.

One key aspect that utilities require when introducing technologies based on high temperature superconductors (HTS) such as fault current limiters (FCL) is assuring coordination of protections. Under a short-circuit event, FCL limits current and the fault could potentially remain undetected. This is easily addressed by measuring voltage drop at the terminals of the FCL, which will abruptly increase under the fault. Yet, a different problem arises in e.g. inductive FCL of transformer type with superconducting secondary. If one or more turns of the latter quench under normal grid operation, an inductive voltage develops due to increased linked flux and a false short-circuit is identified by protections. In this paper, a method to address this problem is presented envisaging the mentioned FCL topology with short-circuit secondary built by second generation (2G) HTS tapes. The proposed approach is based on flux density measurements obtained from a matrix of hall sensors perpendicular to secondary tapes and intends to provide a simpler solution when comparing to common voltage monitoring of sections of turns, which may also become unfeasible in such applications. The methodology is developed based on finite elements simulations and is validated in a single-phase prototype.

The recent progress in critical current density of 2G HTS makes necessary to adjust the stabilization in order to ensure the thermal stability of the tapes during operation. This item is particularly important with respect to the application in fault current limiters (FCL).
On the one hand the 2G HTS tape in FCL has to carry the required nominal current under normal operation condition, on the other hand the resistance must be sufficiently high in the case of limitation. In addition the same tape has to withstand without degradation any possible operating condition, in particular any possible electrical field and over-current or fault in the device. During each overload case, the wire is absorbing the energy of the quench with its heat capacity. Thus, with increasing critical current density also the electrical stabilization has to increase. The needed additional stabilization is a compromise between the limiting ability of FCL and the thermal stability of the wire.
Applying additional stabilization such as electroplated copper or laminated stainless steel foil in addition to the basic Ag-sputtered layers makes possible a taylor-made customization of the 2G HTS with respect to the specific application case.
In this work the thermal stability was investigated experimentally by qenching several commercially available tapes with different stabilizations and critical current densities. The electrical field and the prospective current were varied to identify the experimental conditions with the maximal risk of overheating. Special attention was given to the spatial distribution of the quench in partial load cases. With these experiments, the most dangerous operating conditions were identified.
The planned application is an air coil superconducting fault current limiter (SmartCoil).
Keywords:
Coated Conductor (CC), Fault Current Limiter (FCL), 2G HTS

This work is supported by the German Government under Grant 03ET7525B (project SmartCoil)

In recent decades, the scientific community has made great progress in the development of fault current limiter (FCL) devices to protect electric and electronic equipment against electrical faults, especially in urban areas. Such electrical faults may result in temporary or permanent damage to electric equipment, e.g., uninterrupted power supplies, electronic devices, electric motors, transformers), which may require a change in hardware. Hence, it is essential to develop protection devices which can suppress the electrodynamics and the thermal stress on electric equipment, including circuit breakers and fuses, during an overcurrent state.
A superconducting fault current limiter (SFCL) represents a good solution in terms of reliability, weight, volume, stability under normal operating conditions, self-triggering capability, sensitivity to faults and abnormalities, and quick action time (on the order of 4 ms). From this viewpoint, researchers have proposed the hybrid operation of SFCL and conventional protective devices]. Under fault current conditions, the SFCL can act during 5 cycles (80 ms).
In this scenario, use of ceramic superconductors at large scale depends on solving certain persistent problems. The main issue is grain inhomogeneity in bulk samples, which leads to the formation of weak zones characterized by low critical current and critical temperature values. Therefore, it is essential to determine the maximum time and transport current that the ceramic can support under a fault condition such that their effects are reversible.
In this work, we has assessed the performance of a small resistive superconducting fault current limiter based on polycrystalline SmBa₂Cu₃O_7-d (Sm-123) subjected to 750 short-circuit events with acting time 80 ms. Preliminary results indicate that polycrystalline Sm-123 cuprates can be used to build superconducting fault current limiters. The results of this study have demonstrated that after 616 short-circuit repetitions, the superconducting element was able to limit the fault current without degradation on low-level fault current density J< 3.7 kA_peak/cm².

The authors would like to express their gratitude for the financial support provided by the CAPES and FAPES (#60062851/2012) agencies.

Superconducting fault current limiters already demonstrated their viability in power grids. They can support the increased penetration of dispersed generation, namely from renewable sources, by avoiding or postponing investments in upgrade of protections, due to limitation of short-circuit levels. In order to disseminate these technologies it is required to develop design tools that allow meeting utilities requirements, as current maximum peak under a fault, and adjusting to grid specific characteristics, as short-circuit power. These tools must take into account the properties of constitutive elements of the limiter, namely iron core and superconducting tape characteristics, when considering inductive limiters of saturated cores type.
This paper presents a design methodology that allows modelling and simulating saturated cores superconducting fault current limiters based on the aforementioned characteristics of their constitutive elements and aiming addressing utilities requirements and grid characteristics. A laboratory scale prototype is built and tested in order to validate the methodology, allowing comparison of experimental measurements with simulations and verification of accomplishment of requirements.

We suggested the superconducting fault current limiter (SFCL) using two magnetically coupled shunt-reactors, which can limit the fault current with two triggering current limiting levels. In the suggested SFCL, the fault current with the higher peak amplitude makes second HTSC element connected in parallel with one of two magnetically coupled shunt-reactors to be quenched after the first HTSC element connected in parallel with another shunt-reactor is quenched, which contributes to the higher limiting impedance of the SFCL. On the other hand, the fault current with the lower peak amplitude right after the fault occurrence causes the only first high-TC superconducting (HTSC) element connected in parallel with one of two magnetically coupled shunt-reactors comprising the suggested SFCL to be quenched, which the fault current can be limited through the lower limiting impedance of the SFCL.
Therefore, the effective fault current limiting operation of the SFCL can be expected to be performed by generating the SFCL’s limiting impedance in proportion to the peak amplitude of the fault current.
Through analysis on the various fault current limiting tests with the SFCL using two magnetically coupled shunt-reactors, the proper design for the more effective peak fault current limiting operation of the SFCL using two magnetically coupled shunt-reactors was discussed.

The high growth of electrical power on ships (propulsion, electric arms for military ships…) leads to modifications and optimizations of their electrical grid, from their architecture to their components. An emerging architecture is the DC distribution, which outperforms the AC solution. Security and protection are two major concerns on a ship. Even with controllable static converters, fault currents may be very high. For security reasons there are in general a port grid and a starboard grid. They are not connected in normal operation in order that a fault (short-circuit) on one grid has no influence on the other grid. On the other side a coupling brings a lot of advantages through mutualisation and due to a stronger grid. This coupling is possible using a superconducting fault current limiter (SCFCL). A SCFCL limits the current amplitude by automatically inserting a high resistance which « isolates » the fault. A SCFCL between the two ship grids appears as a promising solution to take benefit of the coupling in normal operation and the decoupling in case of fault. Simulations have been carried out to study the operation and the advantages of such SCFCL implementation, with consequences in terms of safety as well as protection. A demonstrator is under development. It uses YBCO pancakes with several configurations: low or high inductances, series or parallel electrical connexions. The rating is 500 A – 1600 V or 1000 A – 800 V. The design of the demonstrator, of its SC element (design of the YBCO tape) in particular and preliminary tests will be presented.

The research leading to these results is by the French DGA in the INSERE HT project.

Lightweight MW-rate power cables in electric aircraft propulsion systems will allow reducing fuel consumption by more than a half. Taking into account the low voltage limitations for onboard use, superconductivity providing high current carrying capacity becomes an enabling technology for this application. In the frame of a preliminary study of a superconducting power distribution grid we have fabricated and tested a high temperature superconducting (HTS) Roebel cable. The work was done by a consortium of Institutions and supported by Airbus Group Innovations. SuperOx provided a 400 A-class 12 mm wide 2G HTS wire. The team at Karlsruhe Institute of Technology prepared seventeen 5.5 mm wide Roebel strands with a transposition length of 226 mm and assembled the strands into a 6 m long Roebel cable. The team at Russian Scientific R&D Cable Institute performed characterisation of the cable. Short samples of the cable were tested to determine their critical currents, mechanical properties and stability during thermocycling. For a 4 m long section of the cable we measured the critical current, as well as transport AC losses at different frequencies in the range from ~ 40 to ~ 400 Hz. In the paper the cable design and test results are presented. The feasibility of using 2G HTS Roebel cables in electric propulsion aircraft systems is discussed.

Triaxial HTS power cables are the optimal solution for low and medium voltages. This design permits to save expensive HTS conductor and to increase the power density transmitted. Two full sizes and long “triaxial” cables with 10 – 13.2 kV ratings were developed . The HTS “triaxial” cable with 1 km length is installed in grid in Essen, Germany. In Russian Scientific R&D Cable Institute in the framework of the ship propulsion system development has been developed 10 m prototype of HTS “triaxial” cable with 1 kV/ 2 MVA ratings. The computer simulation of the cable with three superconducting layers and outer copper shield has been performed. The optimal twist pitches to minimize magnetic fields around a cable have been determined. The cable has been inserted in a full size flexible cryostat with current leads developed and tested at DC and AC conditions. The DC critical currents were determined for each layer. AC losses have been measured at different frequencies from 37 Hz to 350 Hz. The cable design, test results and their analysis are presented.

The socio-economic aspects of superconducting transmission lines (MgB2 and HTS) will be discussed and compared with the state-of-the-art HVDC overhead lines and underground cables based on standard (resistive) conductors. This includes cost, technical advantages, environmental aspects and right-of-way requirements. The multiple positive characteristics of superconducting power lines make them an ideal choice not only for niche applications, but also for general power transmission and distribution in the future electricity grid.

Superconducting transmission lines have a tremendous size advantage, potentially much lower total electrical losses for high-capacity transmission besides a number of other technological advantages. The capital cost can be lower compared to solutions based on standard conductors. That makes them very attractive for transmission and distribution system operators when it comes to upgrading and installing transmission systems in congested areas likely challenged by public acceptance issues. As a result of the mentioned advantages and the higher public acceptance, the approval time could be significantly reduced for such a superconducting line.

At IASS the possibility of replacing standard HVDC lines with DC superconducting cables is investigated. Our research is focused on the possibility of using the superconductor magnesium diboride for high-capacity long-distance electric energy transport. The cost per kA-meter is much lower for MgB2 than for high-temperature superconductors even when assuming the same operating temperature of 15-20 K.

IASS works in cooperation with several international partners from industry and research as well as with TSOs to show the technical feasibility and reliability of MgB2-based high-capacity transmission lines.

Offshore renewable energy, such as wind, tidal and wave energy, represents a potential solution to the future energy demand. Consideration has been given to the development of offshore wind, tidal and wave farms, particularly in Europe, North America and Asia. Many projects have been approved and several farms are already under construction. To integrate these offshore farms and transfer power from them to shore-based power networks, comparing to conventional copper/aluminum cables with limited power capacity and considerably high transmission lose, more capable and efficient submarine power cables are urgently required. Superconductor, which is being applied for developing continent power cables so far, is a perfect option.

As the head of Applied Superconductivity Centre in the University of Edinburgh, I will for the first time present our research work on applying superconductors to develop superconducting submarine power (SSP) cables. Such SSP cables are expected to entirely upgrade the present power network.

Both advantages and potential risks of SSP cables will be presented, followed by analysis of their reliability. An SSP cable with suitable configuration for submarine power transmission is proposed. Based on numerical modelling, its electrical and magnetic properties are studied and its loss characteristics are analyzed. Results show that the SSP cables can greatly benefit submarine power networks with ultimate power capability and extremely low loss. However, efficient cooling is essential along with the protection of physical damage and fault current. All results will be presented and relevant discussion will be carried out.

Reduction of heat leakage is a key issue for development of superconducting practical devices. We evaluated thermoelectric performance of Peltier current leads (PCLs) designed for superconducting direct-current transmission cable systems using a custom-made test-bench. The test-bench consists of a vacuum chamber, a reservoir tank of liquid nitrogen and a digital mass flow meter. A pair of (n- and p-type) PCLs was connected to the reservoir tank with copper leads and the amount of heat leakage through PCLs was evaluated from the evaporation rate of liquid nitrogen in the tank. The result indicated that the amount of heat leakage, Q, was about 6 W at I = 0 A, and showed the minimum at around 50 A, then increased as the current increased and reached about 12 W at 175 A. We also evaluated Q/I to estimate the heat leakage as a cable system. Q/I showed the minimum at around I = 130 A, and the amount of heat leakage was estimated as ~30 W (per one terminal) for a 1-kA cable system.
Heat leakage depends on a lot of parameters of the PCLs, not only the physical properties such as resistivities, absolute electromotive forces (Seebeck coefficients), thermal conductivities of Peltier elements, but also the geometrical factors such as the cross-section and the lengths of Peltier elements and copper lines. We estimated heat flows and the energy balance inside the PCL by measuring temperatures and voltages of the Peltier elements and the copper lines, and investigated the possibility of further reduction of the heat leakage of the system.

This work was supported in part by a grant of Strategic Research Foundation Grant-aided Project for Private Universities from the Ministry of Education, Culture, Sport, Science, and Technology (MEXT), Japan.

A demonstration project of the DC superconducting power transmission line using the BSCCO wires, was started in 2013, Ishikari, Japan, as a national project (‘Ishikari project’). In the project, two power lines will be installed. Line 1 with 500m-long HTS cable will directly connect the "Ishikari Data Center" of Sakura Internet and a photovoltaic cell. Line 2 with 1000-meter cable, which will be the world’s longest experimental transmission system, is planned to be used for verification tests. The design of the cable system was started from April, 2013, and the construction has been started in the field from June, 2014.
One of the key issues for the realization of HTS power transmission system is reducing the heat leakages along the terminal and the cryogenic pipe to improve the cooling efficiency, because the HTS power cable should be cooled to very low temperature, typically ~70 K. In order to reduce heat leak from the terminal, we adopt the Peltier current lead (PCL), which has been developed and tested in the 200m-DC transmission system (CASER 2) in Chubu University [1,2]. In this project, we optimized the specification of PCL and also made the over current test using a test bench in our group. We have also developed a new cryogenic pipe for the Ishikari project, which comprises of two inner pipes, one for installation of a cable and the other for return of the liquid nitrogen, respectively.
In advance to the construction, we evaluate the performance of the individual components of the cable system, such as the cryogenic pipe, the low-heat-leak current lead and so on, using test benches. The design value of the heat leak of the cryogenic pipe that encloses the superconducting cable is 1.5 W/m and the experimental result is 0.7 W/m to 1.5 W/m on the test bench. The design value of the heat leak from the current lead is 35 W/kA and the experimental value is 30.5 W/kA at the rated current. We also show the methods considered to control of the thermal contraction and expansion to maintain cable safety.
We also report on the circulation test of liquid nitrogen for line 1, carried out in this year.
References
1. S. Yamaguchi et al., Physica C 471, 1300 (2011)
2. S. Yamaguchi et al., Physics procedia 36, 1131 (2013)

This work was partially supported in part by the Japanese Ministry of Economy, trade and Industry (METI). We also acknowledge to Professor A. Iiyoshi, the President of Chubu University for his continuous encouragement. The author also thank to all members of the i-SPOT.

Urgent problems of the power industry of the XXI century require the creation of smart energy systems, providing a high efficiency of generation, transportation and consumption of electricity. Simultaneously, increased requirements for manageability of energy systems, environmental and resource-saving characteristics at all stages of production and distribution of electricity. One of the solutions to the many problems of the power industry is the creation of new high-efficiency electrical equipment for intelligent power systems based on superconducting technologies to ensure a qualitatively new level of functioning of electric power industry. Superconducting power cables are one of the most advanced developments in the field of superconducting devices. Taking into account obvious advantages of superconducting cable lines for the transmission of large power flows through an electric network, compared with conventional cables, the Federal grid Company of Unified Energy System (JSC “FGC UES”) was initiated the R & D program includes the creation of HTS AC and DC cable lines. Two cable lines and accessories on the transmitted power of 50 MW at 20 kV were made in the framework of the program. Tests of both types of cables were conducted in the "R&D Center @ FGC UES” JSC, Moscow. The test results presented in the report.



This work was supported by the Federal grid Company of Unified Energy System under the contracts № И-11-21/10 and № 10/12

High temperature superconductors (HTS) are becoming widely used in electrical power applications. Electrical devices that use HTS conductors or tapes with high critical temperature (Tc) and high current carrying capability operate more efficiently and with higher power density compared to the conventional one. The development of technology to fabricate high current density and long length second generation HTS wires and tapes are pointing out YBCO tapes as next promising candidate for AC power transmission cables. Unfortunately, as is well known, HTS exhibit AC loss when exposed to time varying external magnetic field and/or transport current. So, a challenging task in designing appropriate HTS cable is to calculate such loss because it eventually leads to thermal runaway of the cable. However, it is a hard task to accurately determine ac loss and in the last few years this problem has been addressed numerically. Brazil is involved in a R&D project stimulated by its electrical regulatory national agency to design, build and test a five meters length cable HTS three-phase for operation at 69 kV. For such we have been done calculations of the several parts that constitutes such cable. In this work we present our results numerically obtained using COMSOL Multiphysics for the electromagnetic, thermal and mechanical properties of the dielectric, metals and YBCO Superpower tape presents in the cable. Also we present here our results for the numerical simulation of cryostat of the cable and that of the cable as a whole. Where it was possible to compare, we verify that our results are in good agreement with others in the literature.

P&D ANEEL D712: SUPERCABO Project, CEMIG D, CEMIG GT, CTEEP, TAESA, TBE, UFRRJ and FAPUR for financial support.

The new HTS cable project supported by New Energy and Industrial Technology Development Organization (NEDO) started on July 2014 in Japan. Target of this project is to verify and improve the safety and the reliability of high temperature superconducting (HTS) cable systems. The main verification items are the system safety in case of following; (1) short-circuit accident, (2) ground fault accident, (3) cryostat broken accident by experimental and numerical simulation, and we also develop the technologies such as (4) low heat loss cryostat and (5) high efficiency cooling system. Tokyo Electric Power Company studies the assumed accidents and examination methods. Sumitomo Electric Industries, Ltd. conducts the safety and the reliability tests of 22 kV and 66 kV cable systems and testing of cryostat damage accident for the cable, and Furukawa Electric CO., LTD. and Fujikura Ltd. conduct these tests of 275 kV cable system. MAYEKAWA MFG. CO., LTD. works on the performance improvement of cooling system.

One of the obvious trends in the field of transportation systems (automotive, for example) is gradual transition to the electric drivetrains. This happens since several clear advantages: high efficiency of electric motors, reduction of the size of the traction drive, operating with zero emission etc.
At the same time, for the number of applications at the transportation systems, technologies of applied superconductivity can provide even greater benefits. Namely: reducing the size and increasing the efficiency of up to 99%, the possibility of creating electrical machines with high specific power etc.
In MAI-based "Center of Superconducting machines and devices" has been designed and tested a 200 kW synchronous motor with excitation coils based on 2G HTS tapes for transport applications. This electric drive is designed for installation on the electric buses.
Designed HTS motor has the following main parameters: nominal phase voltage — 450 V, 3 phase, 6 poles, nominal stator current — 165 A, nominal speed — 1500 rpm, maximum speed — 4000 rpm, nominal moment — 1300 Nm, dimensions of active zone – 220x340 mm, power factor — 0.95-0.99, nominal efficiency (without cooling consumption) — 0.96.
This synchronous motor has field winding based on 2G HTS coils in the rotor. In these coils the AMSC tape was used with the following parameters: width — 4 mm, Ic=100 (77 K, self-field, copper laminated). HTS coils were made according to the technology of "double pancake". At the one pole were located three coils with 204 turns totaly. Field coils were made and preliminary tested. The test results are presented.
Stator windings of the motor are made of copper and operate at the environment temperature. Also water cooling on the stator was made.
The rotating rotor cryostat is located on the outer diameter of rotor. As a thermal insulation was used a special material — "Cryogel-Z". Cooling of HTS field coils is provided via liquid nitrogen at the temperature from 65 to 77 K. Special designed cryogenic system is operated at closed loop.
First experimental studies of 200 kW synchronous motor with HTS-2G field-coils will be held at autumn 2015.
Theoretical results and the first experimental results of 200 kW 2G HTS electrical motor will be presented and discussed at the EUCAS-2015.

This work is done within the frames of national program "Superconductivity Industry" supported by "Rosatom".

Superconducting synchronous generators have been proposed for 10-20 MW direct drive wind turbines to reduce the cost of energy of offshore wind power conversion. As a synchronous generator with a superconducting field winding always operates with AC magnetic fields imposed from the armature winding, the AC losses need to be considered. The superconducting field winding, although rotating synchronously with the fundamental component of the armature winding field, is subjected to space field harmonics. These space harmonics come from the armature winding distribution and from the slotting effect when using iron teeth. To reduce the cryogenic load and to simplify the thermal design, it is necessary to suppress the AC losses by a careful design of the armature part. This paper presents a model that calculates the AC losses of a superconducting field winding with MgB₂ tapes. Three scenarios that approximate the geometry of multi-filamentary MgB₂ tapes are presented. The model takes into account the distribution of magnetic flux density and it is used to calculate the distribution of AC losses throughout the cross-section of a superconducting field coil. This method is then implemented to compare the AC losses of four superconducting generator designs with iron and ironless armature teeth. The results show large differences in the AC loss level between the machines with iron and ironless armature teeth.

This work is part of the INNWIND.EU project supported by the FP7 framework of EU, under grant agreement No. 308974.

Superconducting machines have superior characteristics in terms of high power density as well as high efficiency. Recently the research based on 2G HTS machines is under the spotlight. During the operation of an HTS machine, the HTS field winding is exposed to complex magnetic conditions, including time-varying transport current and external AC ripple field both being the reason for AC losses. These AC losses are a crucial factor in connection with the evaluation of machine performance and therefore have to be taken into consideration when designing the cryogenic system.This paper describes results from extensive simulations on the AC losses of 2G HTS machines. The model used in this study is H formulation based on COMSOL and the homogenization method has been implemented to simplify the problem. AC losses in three different operating conditions in superconducting machines are investigated: ramping-up current in no load case where the slope of ramping up is varying; a DC transport current with external AC ripple field in normal operating condition; three-phase short circuit fault condition. The model developed in this paper can evaluate the AC losses in superconducting machines effectively and can be easily extrapolated to large HTS machines.

Hysteretic losses in multi-filamentary MgB2 superconductors embedded in Ni matrices are computed by means of 2D Finite Element Method (FEM) simulations. We estimate the energy dissipation in the rotor of a synchronous superconducting generator for wind turbine applications. Particular interest is given to the losses caused by the magnetic flux ripples coming from the stator. The model considers the nonlinear properties of both the superconducting material and the Ni matrix. A power law E-J relationship together with a nonlinear dependence for the critical current density on the magnetic flux density Jc(B) is used. At the same time, a nonlinear relative permeability models the magnetic behavior of the Ni matrix. For performing simulations, three cross sections are considered: a first one, coming from a micrograph cross section of the tape a second one, created after simulating the elastoplastic deformation of a nickel circular cylinder and a final one, given by an elliptic cross section that is used to validate the modelling technique through a comparison with well stablished analytical expressions. The FEM model used to calculate the losses is based on the H-formulation of Maxwell's equations. Three transposition cases of the filaments are presented indicating full, partial and no transposition. To understand the behavior of the superconducting tape in the rotor of a synchronous generator, the following conditions are studied: Bias-DC current, ramping current under ramping background field, and magnetic flux ripples under DC background current and field.

The authors thank Tecnalia Research & Innovation for providing useful data. First author thanks Coordinación de Estudios de Posgrado (CEP-UNAM) and Consejo Nacional de Ciencia y Tecnología (CONACYT) for financial support. Second and fourth authors acknowledge the support from the Helmholtz Association (Young Investigator Group grant VH-NG-617).

The construction and the tests of an axial-field high temperature superconducting (HTS) machine with an integrated magnetic coupling are described. The originality of the prototype concerns the torque transmission from the cold inductor to the load at room temperature. This constitutes an interesting alternative to torque tubes currently used in HTS motors and generators. This drive solution has multiple advantages: less thermal losses, less vibrations on the shaft, natural protection against over loads, etc.
The HTS machine consists of a 3-phase stator with copper windings, a HTS rotor and a permanent magnets (PM) rotor. The HTS rotor contains 8 pancake coils, made of BSCCO tape, manufactured in our Laboratory. Four coils (double pancakes) create the magnetic field which interacts with the stator field (machine side). The four remaining coils (single pancakes) are used to transmit the torque to the load connected to the PM rotor (coupling side).
The HTS rotor has been immerged in a fiberglass cryostat and cooled at 77 K (liquid nitrogen). Several tests have been carried out as follows
Voltage vs. current curve of each manufactured coil has been measured to check its integrity,
Static torque measurements on the PM rotor have been performed for several current values and load angles,
No-load and short-circuit tests allowed us to determine the equivalent circuit parameters,
Load tests in generator mode at rated conditions showed a smooth and effective power conversion.
Most of the measured external quantities have been checked by 3D finite element computations. A good agreement is noticed.

The authors would like to thank the DGA (Direction Générale de l'Armement) for funding this work.

Linear motors are applied in the semiconductor industry for highly dynamic positioning, for example in photolithographic equipment. Motors incorporating superconducting tapes potentially achieve a higher force density, which allows for an increase of throughput. Although some implementations of linear motors incorporating superconducting materials are known, no design method is available which takes into account the AC losses.
This paper compares motors with superconducting coils in the stator with or without a ferromagnetic core, and with permanent magnets or copper coils in the translator. The currents in the superconducting coils are commutated for the moving-permanent-magnet motors and are DC for the moving-coil motors. One period of a typical motion profile of the application is considered for the transient loss calculation.
AC losses are calculated by coupled static vector potential and transient H-formulation finite element models. YBCO superconducting tapes with a non-magnetic substrate are modeled, taking into account the dependency of the critical current density on the magnetic flux density. The finite stacks of tapes are modeled by homogeneous bulk elements. Losses are calculated for a range of temperatures, number of windings of the superconducting coils, tooth widths of the core, and peak values of the current through the superconducting coils. The maximum force density of a motor is achieved when the average AC losses equal the low-temperature cooling power of the cryocooler, for which a fixed input power is considered.
The calculations show that the moving-permanent-magnet motor with a ferromagnetic core achieves the highest force density, while the coreless variant has excessive AC losses. In the moving-permanent-magnet motors the ratio of optimum peak current to critical current decreases with decreasing temperature, while in the moving-coil motors this ratio is close to unity for the considered temperatures.