bluuebunny/crossref_metadata_2025_split huggingface dataset:
AC Losses Analysis in stack of 2G HTS tapes in a coil
Authors: Zubko V V , Fetisov S S , Zanegin S Yu , Vysotsky V S 
Published: June 2020

Abstract
The model coil with the racetrack geometry based on second generation (2G) High Temperature Superconducting (HTS) tapes has been developed for an electrical machine where a winding pack is a stack of 2G HTS tapes. It is important to evaluate transport current AC losses and possible methods to reduce them in a winding. In a device made of 2G HTS tapes, the main the AC losses are the hysteresis ones. Only numerical simulation permits to predict them in full. The FEM model for calculation of the hysteresis losses developed before for 2G HTS power cables was modified for a stack of the 2G HTS tapes in a coil. In this paper the methods to increase a computational speed are presented. Possible ways to reduce AC losses are discussed also. The details of the model and comparisons of calculations with measurements of the AC loss are presented.
Magnetic shielding of long paraboloid structures in the inhomogeneous magnetic field
Authors: Kvitkovic J , Burnside K , Zhang M , Pamidi S 
Published: June 2020

Abstract
Shielding efficacy of the high-temperature superconducting (HTS) magnetic shields depends on the superconductor properties and on the orientation of the external magnetic field. For precise magnetic field measurements in areas with changing direction of magnetic noise it is important to reduce both the parallel and perpendicular components of the magnetic field. We have designed and fabricated magnetic shields of 25 cm long paraboloid shape with closed sides from second-generation HTS tapes. We have characterized HTS shields in DC and variable frequency AC magnetic fields at 77 K above a copper electromagnet acting as the source of inhomogeneous magnetic noise. The HTS magnetic shields reduce the magnetic field noise penetration and enhance the sensitivity of magnetic field sensors. The measurements were performed with the magnetic shield placed between the noise source and the sensor. 2D finite element analysis using Comsol model was generated and the results were compared with the experimental data of magnetic field dependences of the shielding factor (SF).
Study on conditions to reuse quenched HTS coil
Authors: Toriyama H. , Nomoto A. , Ichikawa T. , Takao T. , Nakamura K. , Tsukamoto O. , Furuse M. 
Published: June 2020

Abstract
An HTS coil quenches despite of the high quench margin. Main origins of unexpected quench of HTS coils are non-reversible local defects, and training effects as in LTS coils are not observed in HTS coils. Therefore, when an HTS coil is quenched before the required coil performance is met, the coil cannot be reused unless the coil is safely protected from quench damage and its operating conditions are readjusted. This paper studies on the conditions to reuse the coil which experienced a quench and is not damaged by the quench to meet the required performance. The study is conducted based on the temperature and current dependences of the coil stability measures of the maximum allowable defect (MAD) and minimum propagating zone (MPZ).
Development of a 20 T 100 mm Cold Bore Superconducting Magnet System
Authors: Ma W , Hollis T , Viznichenko R , Twin A , Clarke N , Warren D 
Published: June 2020

Abstract
Oxford Instruments has successfully developed a series of large bore, high field magnet systems, using conventional NbTi and Nb3Sn low temperature superconductors (LTS). These magnet systems built to date have cold bores ranging from 150 mm to 250 mm diameter with central field from 15 T to 19 T. In this paper, we will introduce the development of a new member of high field and large bore magnet system at Oxford Instruments, with a central field of 20 T and cold bore of 100 mm. The magnet will be integrated with a special low-loss cryostat, generally stainless-steel construction with conductive radiation shields, constructed to minimize eddy currents and reinforced to withstand induced forces in the event of a magnet quench. The key technical challenges which must be met to provide such magnet system will be discussed in this paper.
Magnetic Field Leakage of HTS Medical Accelerators
Authors: Baird Yvonne T E , Li Quan 
Published: June 2020

Abstract
A high temperature superconducting (HTS) magnet used in medical accelerators was designed with combined function for bending and focusing/defocusing, through a layer-by-layer design process. The six-layer combined function magnet produced by the layer-by-layer design process reduces the total volume of HTS material required compared to existing designs, in addition to achieving a precise field. The magnetic field distribution and leakage from the coil ends of the designed combined function magnet were studied, and the effects of changing the length of the coil ends as well as the radius of the layers were compared to the original design, to determine what influence this would have. Results show that shorter coil ends have the smallest leakage magnetic field, and is thus preferred, however due to mechanical constraints of HTS tape there will be a minimum length requirement depending on the design.
Feedforward current control of MRI magnet with power supply driven operation
Authors: Kitada S. , Sakamoto R. , Shirai Y. , Yokoyama S 
Published: June 2020

Abstract
We have been developing a conduction cooled 3T HTS(REBCO)-MRI system. The prototype system of 100 mm DSV (diameter spherical volume) was designed and made.The MRI image of a mouse fetus (25 mm long) was obtained successfully with 2.9 T under a power supply driven operation. However, the HTS(ReBCO)-MRI magnet still had a considerable magnetic field fluctuation for clear MRI imaging due to a long-lasting attenuation of screening current induced on the superconducting tapes. To solve this problem, we introduced a power supply system consists of a exciter power supply and a small trimming current supply, which compensates the magnetic field deviation due to the screening current, in parallel. We measured and evaluated the magnetic field stability of a commercial 3T-LTS-MRI magnet under both the power supply driven operation with proposed system and the persistent current operation. The availability of the power supply system was discussed using an experimental HTS-MRI system.
A target field approach to optimize cylindrical shim coils for superconducting MRI system
Authors: Wu Kaihong , Shi Yi , Wu Yu , Xu Aihua , Hao Qiangwang , Dai Chao , Ma Yuanyuan , Zhang Yongliang , Hussain Muhammad Talib 
Published: June 2020

Abstract
Target field method is used to design a specific form of the magnetic field which has been verified in many works of literature. And to restrict the current distribution on a rectangular or cylindrical surface with finite size, the current density is usually expanded by Fourier series with some unknown coefficients, which can be determined by setting the target-field points over the imaging region of interest, and then comparing the calculated field values from the Biot–Savart law and the ideal ones. The stream-function method is adopted to discrete the current density to generate winding patterns. But some design results can’t match the predetermined ones. Based on it, this paper proposed a new strategy for cylindrical shim coil design. Finally it can make the final design values meet the ideal fields with limited errors. This method can also be used to design gradient coils for high field superconducting MRI systems.
Development of a Half-Size 3 T REBCO Superconducting Magnet for MRI
Authors: Miura H , Matsuda T , Nomura K , Inoue T , Morita Y , Eguchi R , Otake S , Tanabe H , Yokoyama S , Sato S 
Published: June 2020

Abstract
We have been developing a liquid-helium-free 3T magnet for MRI using high-temperature superconducting (HTS) wires in a HTS application project supported by the New Energy and Industrial Technology Development Organization (NEDO). A half-size 3T-MRI magnet, which has 220 coils each of order meter size, has been manufactured in order to demonstrate MR imaging. 269 REBCO single-pancake coils were manufactured. We investigated the yield rate of meter-class REBCO coils by experiment and the degraded state of coils by calculation. It was found that the yield rate was 82 % and the degraded length was order millimeter size in total length of coil, which was several hundred meters. We will consider the factors of coil degradation and how to increase the yield rate of a REBCO coil.
Simulation of AC losses in racetrack coils wound with striated HTS tapes
Authors: Bianchetti M , de Bruyn B J H , Krop D C J , Lomonova E A 
Published: June 2020

Abstract
The T-A formulation has proved a fast and reliable method for the evaluation of AC losses in superconducting tapes, and has been successfully applied to complex geometries such as racetrack coils, CORC® cables, and twisted stacked tapes conductors in either applied magnetic field or self-field. In particular the T-A formulation was used for the evaluation of AC losses in CORC® cables made of striated superconducting tapes in an external applied field, with a null transport current. In this paper, the T-A formulation is adopted to evaluate the AC losses of stacked striated HTS tapes, representative of the straight section of a racetrack coil, with a sinusoidal transport current.
Quench protection of the BabyIAXO magnet
Authors: Bykovskiy N. , Dudarev A. , Silva H. , ten Kate H. H. J. 
Published: June 2020

Abstract
BabyIAXO, a 20 m-long twin-bore helioscope aiming for search of axion like particles, is currently in the engineering design phase and its construction is to be completed within the next 4 years. In addition to X-ray detectors and focusing optics, the system is equipped with a 50 MJ magnet with a common coil layout, containing two 10 m-long NbTi flat racetrack coils cooled by a group of cryocoolers. It has to operate at 10 kA, preferably in persistent mode with disconnected power supply, allowing to simplify the sun-tracking rotation system of BabyIAXO. A direct current mode is possible as well. Hence, quench protection is a high priority. Here, we present the electrical circuit of the BabyIAXO magnet and its protection layout when operated in persistent mode. The quench process is calculated using a 3-D thermo-electrical model of the coil windings, also accounting for the presence of the coil casing and the quench-back effect. Impact of the operating current, conductor properties, voltage detection threshold and location of hot-spot on the peak temperature is discussed. Quench protection aspects of the HTS busbars and persistent mode switch are also addressed.
AC losses and induced fields in HTS coil wound using two-ply coated conductors
Authors: Yokoyama H , Zhu B , Kajikawa K , Awaji S , Badel A , Takahashi K , Okada T 
Published: June 2020

Abstract
AC losses and screening-current-induced fields (SCFs) in a high temperature superconducting (HTS) inserts for high field magnet are evaluated theoretically. The HTS inserts are composed of stacked pancake coils, which are wound using two-ply conductors, where the superconducting-layer sides of two rare-earth-based coated conductors are attached to each other without electrical insulation. The theoretical formulas of AC loss and SCF in the two-ply conductor are derived for the simultaneous applications of a transport current and an external magnetic field parallel to its broad face. By taking into account the magnetic-field profile in the HTS insert and the magnetic-field dependency of critical current density in the coated conductor, the AC losses and SCFs are estimated using the theoretical formulas for monotonical increase in a central field up to 25.5 T in 60 minutes in combination with low temperature superconducting outsert coils. It is guessed that the AC loss estimated for the HTS insert wound using the two-ply conductor could be cooled by using prepared cryocoolers. The magnitude of SCF in the HTS insert wound using the two-ply conductor becomes smaller than that for the single-tape conductor estimated previously.
Adoption of getter pump for HTS superconducting cable system
Authors: Watanabe M , Masuda T , Yamaguchi H , Tanazawa M , Mimura T 
Published: June 2020

Abstract
For the superconducting cable operation in the real grid for over decades, one of the important technical challenges is maintaining vacuum rate of the thermal insulation cryostat vessels for avoiding system heat loss increase. When the vacuum rate is getting worse, turbo-molecular pumps etc. are usually adopted for that system. However, these pumps need to have some installation space and some electricity for the operation and moreover, periodic troublesome maintenance is needed. For the countermeasure of such issues, getter pump is selected and tested because of its smaller size, less electricity consumption and easy maintenance features. After confirming its effectivity as the vacuum pump by several investigations, this pump was employed for the termination vacuum vessel of the superconducting cable system in Yokohama. From the results of 3 weeks operation, evacuating performance exceeds turbo molecular pump and keeps vacuum state less than 1e-3 Pa stably, are confirmed respectively. This paper describes test results of the getter pump and its operation results for the real in grid system.
Design optimization of high-voltage HTS three-phase cables with screened phases
Authors: Arkhangelsky A Yu , Balashov N N , Degtyarenko P N , Kopylov S I , Zheltov V V 
Published: June 2020

Abstract
Design versions of HTS cables with the screened phases ensuring the AC losses minimization have been investigated by the numerical simulation methods. The following methods of optimization have been proposed: sectioning of phases, using of HTS tapes with the modified configuration and variation of the phase diameter. At the critical current of a phase of 5.1 kA and its rated current of 4 kA, these methods allow lowering of AC losses level to 0.45 – 0.017 W/m what is much lower than natural heat fluxes into a cryostat. The designs proposed are compared with ones of the optimized tri-axial cables what allows a reasonable choosing of a cable type vs. a given electric power system design.
Effect of HTS stack sectioning on pulse magnetization efficiency in a motor
Authors: Smara A , Climente-Alarcon V , Mineev N , Tomkow L , Glowacki B A 
Published: June 2020

Abstract
Stacks of HTS superconductors can be magnetized and used as a surface mounted magnet for electrical machines. Pulse field magnetization is considered as a practical method; however, the amplitude of the pulse can be limited in an electrical motor which results in an under-saturated stack with the superconducting currents penetrating only a part of it making the magnetization less efficient. A solution to this problem could be sectioning the stack along its width enabling effective penetration of the superconducting currents. In this paper we investigate the effect of sectioning of HTS surface mounted stacks on the efficiency of pulse magnetization method in trapping the flux using low pulsing field. It is shown that the sectioning of wide stacks into several narrower parts results in a higher trapped flux at low pulses. Experimental measurements are performed on a lab-scale motor to validate the theoretical analysis.
Development and testing of 10 kW fully HTS generator
Authors: Kovalev K , Ivanov N , Zhuravlev S , Nekrasova Ju , Rusanov D , Kuznetsov G 
Published: June 2020

Abstract
Electrical machines on the base of high temperature superconductors (HTS) could provide high specific (kW/kg) and volumetric (kW/m3) power. The most promising of them are fully HTS machines. Significant number of parameters and factors which have an impact on HTS windings make analytical analysis of the machine very complex. In this paper description of the prototype of fully HTS electrical machine is provided. Manufactured prototype was tested, experimental and calculation results were compared. In particular, open circuit performance is in good correlation with theoretical conclusions. Besides, results of experimental research of 15 HTS coils are provided. Some design features of the prototype are described.
Fault Current Limitation Coordination of Multiple SFCLs in IEEE 14-Bus Test System
Authors: Hayakawa N , Mori Y , Kojima H 
Published: June 2020

Abstract
We have proposed the concept of “fault current limitation coordination” of multiple superconducting fault current limiters (SFCL) to be introduced in a future electric power grid. Using a simplified test system, the transients on fault current and internal phase angle of generators were analyzed by PSCAD/EMTDC and the modeling of resistive SFCL with a variable resistance as a function of both current and temperature at the recovery under load. In this paper, we extended the analyses to the fault current limitation coordination of multiple SFCLs in IEEE 14-bus test system. The effective coordination strategy on the introduction and operation of multiple SFCLs, e.g. introduction lines of SFCLs, operation parameters such as operating current, critical current and prospective fault current of each SFCL, was discussed and optimized for an arbitrary fault location in the test system.
Study on Improvement of Recovery Characteristics of GdBCO Non-inductive coil for resistive SFCL
Authors: Yanai S. , Maeda C. , Shirai Y. , Shiotsu M. , Isojima S. 
Published: June 2020

Abstract
Using the practical application of the resistance SFCLs (Superconducting Fault Current Limiter), it is required to quickly return to the superconducting state after interruption of the fault current. The quick recovery needs to improve the cooling property of a superconducting tape. It is confirmed that the recovery characteristics of a superconducting tape can be improved by the PTFE (PolyeTetraFluoroEthylene) coating or applying pressure. In this paper, we used GdBCO tapes for the resistive SFCL and investigated the effect of the PTFE coating or applying pressure for improvement of its recovery characteristics of non-inductive coil. Besides, we observed the boiling phenomena on the surface of the part of GdBCO tapes between under pressurized conditions and ambient pressure by a high-speed video camera.
AC losses test of HTS racetrack coils for HTS motor winding
Authors: Zanegin S Yu , Ivanov N S , Shishov D M , Shishov I M , Kovalev K L , Zubko V V 
Published: June 2020

Abstract
Current work is dedicated to determination of AC losses of racetrack coils that are intended to be used in HTS motor winding. Coils were tested at temperature of boiling nitrogen with sine waveform current with frequencies from 50Hz to 200Hz and corresponding levels were taken as a basis for comparison. Current waveforms, distinctive for brushless DC and brushless AC motors, induced by high-frequency modulation, were compared. Two coils with same dimensions and numbers of turns, but with different tapes (AMSC/SuperOx) were compared in terms of the levels of losses on described current forms.
Winding Configurations and AC Loss of Superconducting Synchronous REBCO Motors
Authors: Kawagoe Akifumi , Kudou Kazuma , Kanemaru Ryota , Iwakuma Masataka , Konno Masayuki , Tomioka Akira , Izumi Teruo 
Published: June 2020

Abstract
We investigate effects of armature winding configurations on properties of fully superconducting synchronous motors using REBCO tapes. The effect of the configurations on ac losses in the winding tapes due to the changing transvers magnetic fields applied to the tapes in direction of perpendicular to the flat face of the tapes is important. In generally, it is effective to close winding factor to 1 for improvement of properties of motors. For the purpose, the shape of armature windings is better saddle-shaped winding than race-track winding. In this paper, numerical calculations on the properties of fully superconducting synchronous motors using REBCO tapes with 500 kW class were described. Operating temperature was 65 K. In order to demonstrate the feasibility of saddle-shaped winding, test coil with 5 turns were wound with YBCO tapes and then critical current measurements were carried out. The degradation of the properties has not observed.
SMALL-SCALE PROTOTYPE OF A FULLY HTS-2G SIX-PHASE INDUCTION ELECTRICAL MACHINE
Authors: Dezhin D , Dezhina I , Ilyasov R 
Published: June 2020

Abstract
HTS direct drive generators with high specific output mass power and specific output volume power (at the boiling point of liquid nitrogen 77 K) are needed for aviation. Elimination of the reduction unit will reduce the weight of the entire generation system. However, this puts high demands on the strength of the high-speed rotor. Other important requirements are: brushless; the possibility of adjusting the output voltage (by changing the excitation current) depending on the magnitude and type of the connected load; autonomy (no external power supply of excitation current). To satisfy all the above requirements, a fundamentally new technical solution for an electric machine was developed. The generator is a two-package hybrid of the Induction machine with combined excitation. HTS-2G windings (2x3-phases of HTS-2G armature windings and axial excitation coil) are in stationary cryostats on the stator. The rotor has alternating poles of high coercive permanent magnets and ferromagnetic poles. To ensure the alternating magnetic field of the poles of the rotor and to avoid demagnetization of permanent magnets by a counter-directed field of the axial excitation HTS coils, the rotor packages are rotated by one pole. In this case, the demagnetizing part of the axial flux is intercepted by the ferromagnetic pole of the neighboring packet.
Excitation Characteristics of MgB2 Race-track Coil Immersed in Liquid Hydrogen
Authors: Iwami Y. , Matsumoto T. , Hara S. , Shirai Y. , Shiotsu M. , Kobayashi H. , Naruo Y. , Nonaka S. , Inatani Y. , Tanaka H. , Kodama M. , Suzuki T. 
Published: June 2020

Abstract
Our research group has been researched for developing MgB2 superconducting energy apparatus in liquid hydrogen immersion cooling, such as superconducting generators.
In this study, two-pole MgB2 race-track coil, which was a model for a few tens kVA superconducting generator field magnet, was designed and made. This coil consists of two pieces of a similar MgB2 race-track coil which has 529 turn with straight section of 150 mm, bending diameter in the end of section of 100 mm and thickness of 34 mm. We carried out excitation tests of the coil immersed in liquid hydrogen at the temperature of 21 K to 32 K, and the load line of the coil was obtained. The critical current under self-field was obtained for various temperatures. The normal zone propagation behavior of the coil at the quench was also investigated using several potential taps installed in the coil.
Trapped-flux magnets characterization for application in synchronous machines
Authors: Climente-Alarcon V , Smara A , Mineev N , Tomkow L , Glowacki B A , Reis T 
Published: June 2020

Abstract
Trapped-flux magnets comprising stacked superconducting tape constitute a promising development to increase the power density of electrical machines, whilst at the same time keeping the complexity required in their construction in manageable levels that allow their use in applications such as aircraft propulsion.
However, the conditions in which superconducting stacks operate inside an electrical motor differ quite significantly from the materials characterization experiments commonly developed to model their behaviour. This work presents the results of studying the applicability of these devices as magnetic flux source in the rotor of synchronous machines considering the influence of whole magnetic circuit. Several aspects are assessed, such as flux harmonics, magnetization, losses and demagnetization. Analytical expressions, which provide limited accuracy but allow fast calculations, are used for this purpose. The results illustrate the different trade-offs that arise during the design of a synchronous electric motor using trapped-flux magnets.