bluuebunny/crossref_metadata_2025 huggingface dataset:
Nb sheathed MgB2 superconducting tape with addition of VB2
Authors: Da Silva L B S , Andreotti L A , Rodrigues D
Published: June 2020

MgB2 superconductor is a strategic material for practical applications, due to its superconducting properties as well as the low cost of the raw materials. For many technological applications cable, wire or tape format are required. The addition of VB2 in the MgB2 superconducting bulk had already been used in previous works as an efficient method to enhance the critical current density of the MgB2. In the present work, MgB2 superconducting tapes were developed and characterized using different amount of VB2 addition. Niobium was used as sheath material. The goal of this work is to create an efficient method to improve the transport properties of MgB2 superconducting tapes to be useful for practical application. The results include microstructural, crystallographic, magnetic and transport characterizations. All analyzes were performed together to study the influence of the VB2 addition on the superconducting behavior of MgB2 tapes.
Heat treatment influence on microstructure and properties of MgB2 superconductor
Authors: Abdyukhanov I , Tsapleva A , Lukyanov P , Konovalov P , Kotova E
Published: June 2020

Study results of 1 mm diameter MgB2 superconductors fabricated by “powder in tube” method are presented. Ti and Nb were used as diffuse barriers materials. The mixture of magnesium and boron, powder of MgB2, and also mixture of magnesium, boron and MgB2 were used to form superconducting compound. Heat treatments in temperature range of 650-700 °C and 750-900 °C for 1h were conducted. It is established that 1 h heat treatment at 700 °C or 1 h at 900 °C heat treatment are sufficient for formation of MgB2 superconducting phase (Tc=38 K) in superconductors with titanium barrier and powder mixture of magnesium and boron or magnesium, boron and magnesium diboride. The Tc of in-situ process Nb - sheated superconductors was 37.6 K, the same Tc were measured for ex-situ superconductors heat treated at 900 °C for 1 h. The critical current measurement results of fabricated superconductors were presented, optimal heat treatment modes were determined for fabricated superconductors.
The Comparative Study of the Internal Tin Nb3Sn Wires with Different Layouts
Authors: Lukyanov P A , Pantsyrny V I , Polikarpova M V , Guryev V V , Novosilova D S , Bazaleeva K O , Tsapleva A S , Alekseev M V , Silaev A G , Abdyukhanov I M , Sergeev V V
Published: June 2020

The required combination of performance properties for internal tin Nb3Sn wires for high energy physics includes high critical current density (J
c) and RRR values as well as low magnetization and effective diameters (Deff
) value. It is quite a challenge to achieve them all at once. A comprehensive study has been carried out on two internal tin Nb3Sn wires with essentially different layouts and 37 sub-elements each. The first type of wires has distributed diffusion barriers. The second one has common diffusion barrier with sub-elements internally divided by resistive separators. Two sets of data for two types of wires have been obtained, which include transport measurements of J
c(B), magnetization loops M(B), superconducting transition temperature (Tc), RRR values, Sn-concentration by EDAX measurements and XRD analysis. XRD analysis of the superconducting layers has shown that the compressive macrostress is larger for the wire with overall barrier than for the wire with distributed diffusion barriers. This observation correlates with a shift of the stress-dependent curves of the superconducting transition. The difference in the volume fractions and the homogeneities of the Nb3Sn phase leads to a significant difference of the J
c(B) dependences and the values of the Kramer critical field (BKr) for these types of wires. In summary, the high critical current density for the first type of wires and the low hysteresis losses for the second type of wires have achieved with high RRR values in both cases.
The magnetic field, temperature, strain and angular dependence of the critical current density for Nb-Ti
Authors: Chislett-Mcdonald S B L , Tsui Y , Surrey E , Kovari M , Hampshire D P
Published: June 2020

A scaling law for J
c in commercial Nb-Ti wire is proposed that describes its magnetic field, temperature and strain dependence. The scaling law is used to fit extensive measurements of the total strand critical current density, J
c,TS(B, T, ε), with the applied field orthogonal to the axis of the wire. We present critical current density, heat capacity and resistivity measurements to obtain

B

c
2

*

(
θ
)

, which shows clear angular anisotropy. At 4.2 K, the resistivity data show

B

c
2

*

(
B
∥
J
)
−

B

c
2

*

(
B
⊥
J
)
≈
1

T

. We also discuss whether the fusion community should consider re-optimising standard commercial Nb-Ti wires that were developed for MRI applications at ~ 5 T, to produce higher J
c at say 10T, and higher upper critical fields, perhaps using quaternary Nb-Ti alloys with artificial pinning centres.
Joining condition dependency of joint resistance in ultrasonic welding of high-temperature superconducting tapes with indium
Authors: Ito S , Hayasaka R , Yuki K , Sato Y S , Hashizume H
Published: June 2020

Ultrasonic welding (UW) is a candidate for easy and simple fabrication of lap joints of high-temperature superconducting (HTS) tapes. Our previous study applied UW to both silver-sheathed BSCCO tapes and copper-stabilized REBCO tapes with indium foil inserted in-between. However, the fabrication was performed with limited joining conditions and critical current, I
C, degradation was confirmed in some of the BSCCO tape joints. In this study, we evaluated the joining-condition dependence of joint resistance and I
C to improve UW-joined HTS tape performance. Various UW samples using BSCCO and REBCO tapes were prepared with different thicknesses of indium foil, ultrasonic vibration amplitude, joining pressure, joining time, and metal plate arrangement. The results showed that HTS tapes layered between metal plates on the top and bottom can avoid I
C degradation even with higher joining energy, however thinner indium foil induced degradation in the BSCCO samples. Through this study, we found the value of joint resistivity only depended on the joining energy per unit joint area. The achieved joint resistivities were 14.0 nΩcm2 for the silver-sheathed BSCCO tapes and 36.1 nΩcm2 for the copper-stabilized REBCO tapes though it was strongly influenced by interface resistivity of the REBCO tape itself.
An electromagnetic method for measuring AC losses in HTS tapes without lock-in amplifier
Authors: Breschi Marco , Filicori Fabio , Musso Andrea , Pasini Gaetano
Published: June 2020

The measurement of AC losses in high temperature superconducting tapes is a complex task due to the small magnitude of the quantities to detect, and to the difficulty to separate the inductive and resistive parts of the measured voltage. This work describes a different approach to the electrical measurement of AC losses, not requiring lock-in amplifiers for the signal processing. The system is based on the acquisition of the voltage and current signals from the sample and their projection on a reference signal, performing a Hilbert transform based treatment procedure. This method allows one to retrieve the harmonic components of the signals with a significant noise reduction, thus improving the quality of the results. The experimental set-up is applied to measure AC losses in different HTS tapes, using sinusoidal currents of different amplitude and frequency. The results are compared with those obtained on the same tapes at other laboratories.
Facility for the Characterization of Planar Multilayer Thin Film Superconductors
Authors: Turner D. , Malyshev O. B. , Burt G. , Junginger T. , Gurran L. , Dumbell K. D. , May A. J. , Pattalwar N. , Pattalwar S. M.
Published: June 2020

The maximum accelerating gradient of SRF cavities can be increased by raising the field of full flux penetration, H
vp
. One method which can potentially increase H
vp
is to use structures consisting of alternating layers of superconductors and insulators (SIS). Magnetometry is commercially available but consists of limitations, such as SQUID measurements which apply a field over both superconducting layers, so H
vp
cannot be measured. If H
vp
is to be measured for SIS coatings, a parallel, local magnetic field must be applied from one plane of the sample, with no field on the opposing plane. A field penetration experiment has been developed at Daresbury laboratory allowing H
vp
to be measured using a local, parallel DC magnetic field. Using a field much smaller than the sample allows limitations such as edge effects to be significantly reduced. By increasing the field, H
vp
can be found by using 2 hall probes, one either side of the sample. The experiment was designed to use a variable temperature insert (VTI) to run in a cryogen free environment, but has been running in a LHe bath for thermal stability.
Developments of NDE method of jacket welds for ITER In-Vessel coil joints
Authors: Liu Xiao-chuan , Qin Jing-gang , Zhou Chao , Chen Wen-hui , Tang Jian-bang , Jomdecha cherdpong , Wu Yu , Chen Zhen-mao , Chen Hong-en
Published: June 2020

The ITER facility currently incorporates two types of In Vessel Coils (IVC) as a method of stabilizing “Edge Localized Modes” (ELM) and providing “Vertical Stabilization” (VS). To withstand the severe conditions, the IVCs are made of stainless steel mineral insulated conductor (SSMIC). The jacket of the SSMIC is modified stainless steel 316LN. The diameter is 59mm and thickness is only 2.5mm. In order to join the IVC coils, it is necessary to develop the joints manufacturing. Jacket welding is an important process of the joints manufacturing. Based on the structural analysis, the maximum acceptable defect sizes inside the jacket weld were defined. This paper presents the non-destructive examination (NDE) development of the jacket weld NDE is the thin thickness which will cause the scattering of sound waves and lead the difficulty of effective identification of defects. Phased Array Ultrasonic Test (PAUT) and eddy current test (ECT) were developed for the jacket welds inspection. The results indicated the feasibility of the PAUT and ECT method could solve the problem of the thin thickness tube weld inspection.
Assembly and Test of the HL-LHC Twin Aperture Orbit Corrector Based on Canted Cos-Theta Design
Authors: Kirby G. , Van Nugteren J. , Mentink M. , Canale M. , Gentini L. , Mazet J. , Pincot F-O. , Mangiarotti F.J. , Fiscarelli L. , Steckert J. , Coelingh G. J. , de Rijk G. , Perez J.C. , Verweij A. , Todesco E. , Rossi L.
Published: June 2020

In the frame of the high-luminosity upgrade project (HL-LHC) at CERN, a double aperture, independently powered, family of beam orbit corrector magnets will be installed close to the two main LHC experiments Atlas and CMS. These 2.6 T magnets, built using a canted cos-theta design. This paper describes the development of the prototype, full size 2-m-long magnets. We first focus on design and assembly techniques: from coil winding using a CNC machined aluminium former to impregnation, layer-jump, quench protection, and yoke assembly. We then present the power test results at 1.9 K: training, field quality and protection.
Design of the consolidated LHC dipole diode busbar insulation system
Authors: Meuter F. , Sahner T. , Scheuerlein C. , Tock J.Ph.
Published: June 2020

During the second long shutdown of the LHC in 2019 and 2020, the electrical insulation of the 1232 dipole diodes and diode busbars is presently consolidated. The newly designed insulation system, mainly consisting of polyimide laminated fiber reinforced epoxy sheets and injection molded pure resin inserts, can be installed in the very constricted space of the LHC tunnel, without removing the presently installed insulation. The consolidated insulation will prevent shorts to ground caused by metal debris in the LHC cold masses and allow preparing the LHC for operation at 7 TeV.
Electro-thermal analysis of the superconducting dipole circuit of SIS100
Authors: Raginel V. , Szwangruber P. , Freisleben W. , Roux C.
Published: June 2020

The heavy ion synchrotron SIS100, the core machine of the new international Facility for Antiproton and Ion Research (FAIR) in Darmstadt, is currently under construction. The 108 superconducting dipole magnets of SIS100 will be powered in series with a cycling rate up to 30kAs−1 which corresponds to 4Ts−1. The dipole magnet protection system considers 12 energy extraction resistors and two crowbars at the outputs of two power converters. As a part of the Failure Mode and Effects Analysis, the most critical failures of the magnet protection system are simulated. In this contribution, initial studies of the electrical and thermal behaviour of the SIS100 main dipole circuit during a quench are presented. The dipole magnet design and topology of the powering circuit (including the protection system) are described. The electro-thermal model in use is detailed. Finally, simulation of a failure mode of the magnet protection system is presented and results are discussed.
Busbar technology development for the HL-LHC inner triplet magnets
Authors: Tsolakis E. , Favier L. , Principe R. , Prin H. , Meuter F. , Scheuerlein C.
Published: June 2020

The busbars for the HL-LHC magnets are made of Nb-Ti/Cu conductor, the insulation system, and the auxiliary equipment to align the busbars with respect to the magnet coldmasses. This paper presents design options concerning the integration of the busbars inside the coldmass with a fixed point, and a reinforced insulation system for the flexible busbar part using thin PEEK tubes. Prototype splices for interconnecting Nb3Sn and Nb-Ti Rutherford cables, and round and flat 18 kA Nb-Ti cable have been produced and first test results are presented.
Distribution Feedbox for the Superconducting Link (SCLink) and Magnets of HL-LHC
Authors: Bailey W , Pelegrin J , Falorio I , Leclercq Y , Betemps R , Parma V , Ballarino A , Yang Y
Published: June 2020

The High Luminosity LHC (HL-LHC) project aims at upgrading the LHC collider to increase its luminosity by about a factor of five. The electrical connection between the magnets in the LHC tunnel and the power converters in a new transverse tunnel will be supplied by a superconducting line (SCLink), consisting of ten MgB2 cables housed into a 140 metre long flexible cryostat. This paper presents the detailed design for one of two types of distribution feedbox, (DFX) located between the magnet and the distribution feedbox. The vacuum barrier required to separate the vacuums of the upper SCLink and lower DFX sections; is to be integrated in the middle of the vertical section of DFX. A detailed study was performed, given the complexity of installing a vacuum barrier with a large diameter within a restricted height. Eccentric loading on the barrier is created by the “L-shape” vessel, necessary to accommodate the transition of the cable from vertical-to-horizontal. The solution considers a vacuum barrier assembly consisting of a flexible corrugated membrane (bellows) and deploys a lightweight “supporting cage” around the barrier and restraining rods in the horizontal section to ensure the barrier bares no substantial load or torque, and suffers no lateral or column type instability during operating and accidental conditions. The current design satisfies the mechanical and thermal design criteria outlined in the DFX specification.
Analysis of short-circuit transients in the LHC main dipole circuit
Authors: Liakopoulou A , Annema A J , Bortot L , Charifoulline Z , Maciejewski M , Prioli M , Ravaioli E , Salm C , Schmitz J , Verweij A P
Published: June 2020

After the occurrence and detection of a short circuit to ground in the LHC main dipole circuit, a fast power abort is triggered and the current in the circuit starts decaying semi-exponentially from a maximum value of 11.85 kA to zero, with a time constant of 103 s. If a short to ground occurs, the current flows through the fuse that is present in the grounding subcircuit. Depending on the value of the thermal load, the fuse first enters a pre-arcing region where it starts intermittently blowing up, until the blow-up threshold is reached, after which it definitively blows up. A simulation scheme utilising a common interface between PSpice and Matlab is proposed in order to simulate the blow-up behaviour of the fuse and hence increase the accuracy of the circuit model for short circuits to ground. A parametric analysis of the short circuit to ground parameters is performed and a better understanding of the behaviour of the circuit under different conditions is obtained. The worst-case values of the voltage to ground in the LHC main dipole circuit are identified for both the case where the intermittent behaviour of the fuse is included in the model as well as for the case where the fuse is not modelled and a comparison between the two is given.
Realisation of Hybrid Trapped Field Magnetic Lens (HTFML) consisting of REBCO bulk lens and REBCO bulk cylinder at 77 K
Authors: Namba S , Fujishiro H , Naito T , Ainslie M D , Zhou D
Published: June 2020

A hybrid trapped field magnet lens (HTFML) can reliably generate a concentrated magnetic field, B
c, in the centre of the magnetic lens higher than the trapped field of the trapped field magnet (TFM) and the applied magnetic field, B
app, even after the external magnetizing field decreased to zero. In this paper, the performance of HTFMLs consisting of EuBaCuO bulk TFM with various heights and a GdBaCuO bulk magnetic lens was investigated at 77 K using liquid nitrogen. A concentrated magnetic field of B
c = 0.80 T was achieved at the centre of the HTFML for the tallest TFM after removing an applied magnetic field of B
app = 0.50 T. The influence of the height of the outer TFM cylinder on the final concentrated field was studied experimentally and discussed using numerical simulation.
Investigation of flux jumps during pulsed field magnetization in graphene-added MgB2 bulks
Authors: Yokoyama K , Oka T , Berger K , Dorget R , Koblischka M , Grigoroscuta M , Burdusel M , Batalu D , Aldica G , Badica P , Sakai N , Muralidhar M , Murakami M
Published: June 2020

MgB2 bulk superconductors are expected to be utilized as rare-earth-free and lightweight trapped field magnets. However, the flux jumps frequently happen during the magnetizing processes, and heavily degrade the field-trapping performances. We have investigated the effect of additives to the MgB2 bulk samples prepared by spark plasma sintering process, and observed various flux jumps during the pulsed field magnetizing processes, which were carried out at 14 K which was obtained by the 2-stage GM cryocooler. The authors classified the flux motions as three categories as “no flux flow”, “fast flux flow”, and “flux jump” regions, and investigated the conditions where the flux jumps happen. We observed some drastic flux jumps in the pristine and clarified the effect of graphene addition to the flux jumps. The experimental results showed us a possible expansion of no flux jump region, and suggested us the improvement of field trapping capability.
Compact 2G HTS power cable: new cold tests results
Authors: Fetisov S S , Zubko V V , Zanegin S Yu , Nosov A A , Vysotsky V S
Published: June 2020

In Russian Scientific R&D Cable Institute we continue studies to develop as compact as possible 2G HTS power cables for electric power systems. Compact cables should have minimized diameter compared to other co-axial HTS cables developed before. Recently we developed the cable prototype with four HTS layers in the core and two layers in the shield. Numerical optimization of compact cables has been used together with manufacturing technology to produce small diameter cables with uniform current distribution. The first cold test of the compact cable demonstrated that we were able to control the homogeneous current distributions in a compact cable with the inner diameter of the core ~10 mm and the outer diameter of the shield ~20 mm. In this work we present more test results of this cable, including, mechanical test and high voltage tests. New test results demonstrated very high parameters of the compact cable developed. The compact cables perspectives for electric systems are discussed.
Development and test of a 35 kA - HTS CroCo cable demonstrator
Authors: Weiss K-P , Fietz W H , Heiduk M , Lange C , Preuß A , Wolf M J
Published: June 2020

The answer to energy-efficient electric power transfer of high currents in the range of several tens of kA can be given by high temperature superconducting (HTS) cables. BSCCO and MgB2 have been used widely for such cables, reaching maximum currents of about 20 kA. REBCO coated conductors are promising for future HTS cables beyond 20 kA and allow the operation based on subcooled liquid nitrogen. Several cabling concepts based on REBCO tapes were developed world-wide to realize such cables. Using the stacked-tape concept, a scalable semi-industrial process was developed by KIT, called HTS CrossConductor (HTS CroCo). Key aspects of the conceptual design of high-current HTS cables are discussed and the design of a 35 kA DC cable demonstrator made from HTS CroCo strands is presented. Aspects regarding joints, current redistribution between individual strands and electrical stabilization are highlighted. The performance of this demonstrator cable was tested, reaching the envisaged current.
The 2nd in-grid operation of superconducting cable in Yokohama project
Authors: Masuda Takato , Watanabe Michihiko , Mimura Tomoo , Tanazawa Masayuki , Yamaguchi Hirohito
Published: June 2020

The superconducting cable system was installed and operated in the real grid of Tokyo Electric Company (TEPCO) Holdings from 2012 to 2013, successfully. At this operation, the system had no degradation of its electrical and mechanical performances. After then, its cooling system was replaced to new turbo-Brayton refrigerator and the cable was re-connected to the grid in 2017. The cable system was successfully operated for another one year. In this operation, stable cooling system controlling, heat loads and vacuum rates of the cryostats etc. were observed continuously. After the operation, No Ic degradation of whole length was measured. In addition, the short sample cables cut from the system after the dismantlement, were applied with AC 90 kV and Imp 385 kV, successfully as the same condition of the shipping test in 2011. These results are one of the credibility confirmations for long time superconducting cable system operation.
Feasibility Assessment of the New Configuration of an Electric Power Grid with 23 kV Tri-axial HTS Power Cables for an Urban Power Supply
Authors: Lee C , Yang H , Choi J , Park M , Iwakuma M
Published: June 2020

The advantage of high temperature superconducting (HTS) power cables is that they can transmit large amounts of power at relatively low voltages, which can be used to reduce the number of lines in transmission cables or to configure a power grid at lower voltages. Because the commercial operation of 23 kV HTS power cables has begun, the optimal configuration between the 154 kV transformer substations and the 23 kV switching stations connected by the 23 kV HTS cables must be reviewed. In this paper, the new power supply model using 23 kV tri-axial HTS cables is presented for an urban power supply, and the economic feasibility is reviewed to present the appropriate cable capacity selection that matches the 23 kV switching stations.
Electrical and cryogenic tests of the 1200 m HTS DC cable system
Authors: Sytnikov V E , Kashcheev A V , Dubinin M V , Ryabin T V
Published: June 2020

Comprehensive tests of all the components of the HTS DC line were carried out as a part of the project to create a superconducting cable line with a capacity of 50 MW for the power system of St. Petersburg. HTS DC cable line will connect two substations of different voltage in the center of the city. The experimental stand included several cable lengths with joints and current leads, a reverse cryostat, a two-circuit cryogenic system with a capacity of 12 kW at 77K, a converter station and a control and monitoring system. The total length of the cryogenic line exceeded 1200 meters. The report presents the results of vacuum, cryogenic and electrical tests carried out over several months. The electrical and hydraulic characteristics of the HTS cable line were determined. Some emergency modes of the cryogenic system were studied. The possible time of cable operation in various accidents in the cryogenic system was estimated.
Heat extraction from HTS tape stacks applied in a superconducting motor in different cooling conditions
Authors: Tomkow Lukasz , Mineev Nikolay , Smara Anis , Climente-Alarcon Vicente , Glowacki Bartek A.
Published: June 2020

The heat is generated inside the stack of superconducting tapes mounted on the surface of the electrical machine rotor during its operation and magnetization. Cooling of such stack presents challenges because of the layered structure of both tape, and stack. Moreover, the tapes should be electrically isolated to minimize the AC losses, that assumes gluing them, rather than soldering. The calculations consider a conductive heat dissipation also through the rotor iron.

Results show that: liquid nitrogen provides an effective cooling; the temperature of the stack shows complex distribution patterns with the gaseous coolant. Additional preventive measures were analyzed to keep the stack operational in vacuum conditions.
Electrical Treeing Characteristics in Epoxy under Electro-magnetic Coupled Field
Authors: Wang M Y , Du B X , Han X T , Li Jin , Li Z L , Xing Y Q
Published: June 2020

Epoxy resin is a kind of material used as electrical insulation in superconducting magnetic devices. The dielectric properties of the epoxy resin directly affect the safety and stable operation of the whole magnet. While operating, the epoxy resin faces the challenges of complex electric field and strong magnetic field. Researches on the effects of harmonic superimposed dc voltage and magnetic field on the electrical treeing behaviour in epoxy resin were carried out. Experimental results show that low-order harmonics are more likely to lead to the extension of electrical tree branches, which mainly results from the higher energy generated by partial discharge under low-order harmonic voltages. Meanwhile, the addition of dc voltage can result in more sever partial discharge because of the asymmetric charge accumulation, and eventually accelerates the degradation process. Zeeman effects were taken into account while considering the effect of magnetic field. More shallow traps are generated under strong magnetic field, thus charges are more easily to migrate under the action of magnetic field and gain enough energy to break the molecular chain. Besides, Lorenz force leads charges to hit the molecular chain more frequently. The above results in the more serious damage in epoxy resin under electro-magnetic coupled field.
Basic research of HTS coil cooling assist technology by magnetic refrigeration
Authors: Hirano Naoki , Nagai Setsura , Xie Yunzhi , Okamura Tetsuji
Published: June 2020

The fundamental research of HTS coil cooling assist technology by magnetic refrigeration has been studied. Using magnetic refrigeration technology, we are focusing on numerical analysis to see if the cooling efficiency around 20 K of high-temperature superconducting coils can be enhanced. The feature of the proposed cooling method is that it utilizes the leakage magnetic field from the HTS coil. Magnetic refrigeration technology needs to apply a change of magnetic field to a certain type of magnetic material, and the configuration of applying a change of magnetic field to the material in the cryostat is the point of the proposed cooling assist method. We confirm a system that uses a magnetic refrigerator in combination with a refrigerant circulation cooling system by utilizing the leakage magnetic field generated when using a superconducting coil and producing a magneto caloric effect has higher refrigeration performance than the refrigerant circulation cooling system alone.
Thermal Transport Properties of Multiple Oscillating Heat Pipes under Simultaneous Operation
Authors: Nagamoto Naohiro , Kawagoe Akifumi , Mito Toshiyuki , Onodera Yuta , Takahata Kazuya , Yanagi Nagato , Hamaguchi Shinji , Hirano Naoki
Published: June 2020

In this paper, it is shown that the results of experiments on which four oscillating heat pipes (OHP) were simultaneously operated. The OHP is formed into board shape and the four OHPs were put radially. Two FRP disks as dummy winding held the OHPs. Stainless steel sheet heaters were inserted between OHPs and FRP disks, to simulate heat generation in the winding. This equipment was cooled by circulation helium gas. The helium gas flowed in the copper pipe. The copper pipe was soldered to copper plates mounted to cooling edge of the OHPs. Four buffer tanks were connected to each OHP to control the pressure of each OHP individually. The working fluid of the OHPs was Neon. It was demonstrated that all OHPs were simultaneously operated.
Directional control of arcs in liquid nitrogen using externally biased magnetic fields
Authors: Junaid Muhammad , Gao Lei , Li Hongxu , Liu Zhiyuan , Geng Yingsan , Wang Jianhua
Published: June 2020

Arc quenching process inside the liquid nitrogen (LN2) can be accelerated by controlling the shape, size and direction of arc plasma through the controlled magnetic fields. This paper demonstrates the experimental investigations of controlling the arcs in specific directions through NdFeB based permanent magnets. The electrodes were shorted by fuse wires to initiate arc plasmas in LN2. The effects of magnetic fields on the arcs inside LN2 were observed for the very first time. The results show that arc plasma can be stretched, lengthened and thinned in the upward and downward directions through the North-South and South-North magnetic fields approach. These findings are good news that arcs can be controlled inside the LN2 environment and several important achievements such as increasing the life time of electrodes, reduction in LN2 consumption, reduction in bubbles formation, reduction in arcing times and getting a regular cylindrical shape, can be obtained through magnetic fields.
Refrigerant circulation system for cooling a HTS coil
Authors: Xie Y , Nagai S , Okamura T , Hirano N
Published: June 2020

When using the superconducting technology industrially, it is not always possible to install a refrigerator near a high temperature superconducting coil for cooling it. In the method using heat conduction cooling, cooling result as expected cannot be obtained due to temperature difference between a refrigerator and a superconducting coil via a heat transfer plate when the distance of the refrigerator and the coil is long. Therefore, a method of cooling a superconducting coil by circulating helium gas has been proposed. Helium gas discharged by a compressor at room temperature is cooled by a pre-cooling heat exchanger, thereafter cooled by a GM refrigerator. The cold helium gas cools the coil and current leads. In this study, the helium circulation cooling system was investigated by using one-dimensional numerical analysis and experiment at different helium gas mass flows.
Loss analysis of superconducting wireless charging for electric vehicles
Authors: Machura P , Kails K , Li Q
Published: June 2020

Wireless power transfer (WPT) is an emerging technology with widespread applications. It can be used for charging in multiple applications, such as wireless charging for electric vehicles (EVs), which has become a major point of interest. Conventionally, it is used for stationary charging, but also dynamic systems emerge. Key drawbacks of standard WPT systems are the limited transfer distance between the copper coils and the transfer efficiency. By employing high-temperature superconductors (HTS) as coil material these limitations can be alleviated. However, HTS coils have an interesting ac loss characteristic which will be studied. This study investigates the transport current and magnetisation loss of HTS coils in the frequency relevant to WPT for EVs. In addition, a comparison between the full anisotropic dependency of the critical current and only considering perpendicular field components is conducted. A homogenous 2D axisymmetric coil model is used to examine three of the most employed coil configurations and their loss characteristics depending on turn numbers.
A Comparative study of transport current loss in HTS coils for superconducting wireless power transfer
Authors: Chen Hongyi , Li Quan
Published: June 2020

This paper focuses on the transport current loss modelling for HTS coated conductor coils under high-frequency AC current, which is essential when applying superconducting technology in wireless power transfer system (WPT). The pancake coil, spiral coil and solenoid coil designs were proposed, whose study were carried out based on the Finite Element Method in 2D using H-formulation. The transport current loss in each layer for each coil when applying high-frequency AC current were simulated in the FEM platform. The variation of the transport current loss distribution from different layers of the HTS coated conductor according to changing current input was simulated and compared for different operating frequencies. Finally, the frequency and current dependence of the transport current loss in different layers was shown and compared. The simulation demonstrates that the transport current loss in copper layer could be much higher than the transport current loss in the HTS layer at high current and frequency level due to the skin effect. The results also present that the pancake coil design and spiral coil design could be applied to relatively lower frequency WPT application while solenoid coil design can achieve lowest total loss in higher frequency application. These results are essential when designing HTS coils for WPT system.
A Novel Configuration for Resistive SFCL with bifilar 2G tapes
Authors: Sotelo G.G. , dos Santos G. , Martins F. G. R. , Sass F. , Rocha L. M. M. , Bitencourt A. A. , Franca B. W. , Dias D. H. N. , de Andrade R. , Polasek A.
Published: June 2020

Electrical faults on medium voltage electric power distribution systems can damage transformers. This fact motivated an R&D project in Brazil to study Fault Current Limiters for a utility. In this context, innovative design with a bifilar winding was developed for the present work, aiming to reduce self-inductance and to improve cooling rate. Long length second-generation superconducting tapes were used to build the prototype, which was constructed on a fiber-glass base. The prototype module has been tested at low voltage levels. The nominal operation, fault current limitation and recovery time have been examined for prospective currents of 2700 A and reduction of about 90 % in the current level. Due to fast recovery time and good heat exchange, the proposed topology has potential to be applied in a full-scale prototype.
Quench-induced Dynamic Breakdown Characteristics of HTS Pancake Coil Model for Resistive SFCL
Authors: Hayakawa N , Mimbu M , Mori Y , Kojima H , Isojima S , Kuwata M
Published: June 2020

Quench-induced dynamic breakdown (BD) characteristics of LN2 under transient bubble disturbance at the quench of HTS tapes are crucial to the reliable and rational insulation design of resistive superconducting fault current limiters (RSFCL). We have been investigating the dynamic BD characteristics using a nichrome pancake coil model for RSFCL using bifilar nichrome tapes as a heater. In this paper, we fabricated an HTS pancake coil model for RSFCL using GdBCO tapes and discussed the dynamic BD characteristics as a function of heat flux generated from the actually quenched HTS tapes.
Experimental AC loss analysis of braid type non-inductive coil for superconducting fault current limiter
Authors: Song W , Pei X , Xi J , Xiang B , Liu Z
Published: June 2020

Resistive superconducting fault current limiter (SFCL) plays a key role to realise the stability and safety of power grid and the future electric aircraft. This paper presents the design and test of a braid type non-inductive coil for SFCL. One inner coil and one outer coil were wound around a G10 tube using 4 mm-wide SuperPower wires. Two configurations of the braid type non-inductive coil were achieved by connecting the inner coil and outer coil in series and in parallel, respectively. AC loss results of these two non-inductive coils were measured and compared to investigate the AC loss dependency on coil configuration and current distribution. It has been concluded that braid type non-inductive coil has low AC loss due to magnetic field cancellation. Serial connection of the inner and outer coils leads to a good degree of field cancellation, which results in higher critical current and lower AC loss of the non-inductive coil, compared to parallel connection.
Study on the Alliance between SFCL and Hybrid DC Circuit Breaker for Protecting HVDC Grid
Authors: Ayachi Amor Yacine , Didier Gaëtan , Leveque Jean , Hamoudi Farid
Published: June 2020

Breaking the DC fault in HVDC grid is the greatest challenge for DC grid protection system. Although there are many scientific researches investigating the high voltage DC breakers, yet, there is still always a trade-off between the interruption time and the breaking capability. Therefore, combining between the superconducting fault current limiter (SFCL) technology with a fast DC circuit breaker could bring a solution to this limitation. In this work, an accurate model of resistive-type SFCL (r-SFCL) considering the electro-thermal behaviour, is proposed to be placed in series with ABB proactive hybrid DC circuit breaker (PHCB). To test the viability of the system, a pole-to-pole DC fault scenario was imposed in a HVDC grid. The numerical analysis was undertaken with (EMTP-RV®) software, while the simulation results show how effectively the SFCL can reduce the fault current below the maximum breaking capability. Also, it is concluded that there is a positive interaction between the r-SFCL and PHCB.
Analysing Faults and SFCL Response in Electric Aircraft
Authors: Alafnan H , Zeng X , Pei X , Khedr M , Zhang M , Yuan W
Published: June 2020

Aircraft technology moves towards electrification in order to achieve environmentally friendly goals. However, one of the main challenges facing the electrification of aircraft technology is the weight of the electric devices necessary for operating a fully electric aircraft. The National Aeronautics and Space Administration (NASA) proposed the use of the superconductive technology in electric aircraft (EA) to overcome this challenge in addition to its other benefits. The proposed EA is called N3-X and it has an on-board DC superconducting network including a superconducting fault current limiter (SFCL). The SFCL is a self-mechanism device that very effectively limits the current within a few milliseconds, thus improving the stability of the system. As the grounding of this network is different from traditional networks, analysing the behaviour of different fault types and how to manage them becomes critical. In this paper, one set of the EA’s systems (one generator, AC/DC rectifier and four motors with their DC/AC variable frequency drives) has been modelled in MATLAB/Simulink environment to carry out the fault analysis and to demonstrate the effect of the SFCL on this network under different types of faults.
Experimental investigation of current limiting characteristics for a novel hybrid superconducting fault current limiter (SFCL) with biased magnetic field
Authors: Zhu Jiahui , Zhang Huiming , Chen Panpan , Zhao Yongqing , Qin Hanyang , Wei Defu , Lu Kun , Dong Yujun , Zhang Ke , Du Qingqin
Published: June 2020

High temperature superconducting fault current limiter (SFCL) is widely considered as an effective protection for power system when the short-circuit fault currents occur. This paper proposes a novel design of a hybrid SFCL with biased magnetic field which has two-stage current limiting characteristics. This kind of SFCL limits the short current using non-inductive superconducting coil at the first stage, and then by the double-split reactor at the second stage, usually 10 ms later. The advantage of this type of SFCL is saving the amount of superconducting tapes, and it is especially attractive in large current and high voltage occasions. A prototype hybrid SFCL with biased magnetic field is designed and constructed in China Electric Power Research Institute (CEPRI) using YBCO coated conductor. A high speed Data Acquisition (DAQ) System based on LABVIEW is established to monitor and control the SFCL. The current limiting ratios for this prototype SFCL have been investigated experimentally under the operating temperature of 77 K. The experimental results show that the current limiting ratio reaches to 89.66% which validates the design and proves the potential application of this hybrid SFCL.
Detailed Review of a Novel Model SFCL for Grid
Authors: Kosa Janos A , Shao Qing , Zhu Huiyun , Yu Yueyue , Vajda Istvan
Published: June 2020

Our paper shows an RL-Indirect SFCL model (RL-I-SFCL). The applied superconducting tape is SF 12100 (Furukawa Electric Group). In the case of the operational current of a grid, the superconducting wire is in a serial connection with the grid as in a resistive SFCL. If we have a short circuit current on the grid, the RL-I-SFCL protection includes an extra inductance. This inductance is in a serial connection with the short circuit current. The change of the resistance of the superconducting wire creates an extra impedance in the main circuit without delay. It is an advantage. We have measured our SFCL and developed a simulation program by using MATLAB program. Hence, we could test our real measured results using a simulation program. We examined only the steady state in fault. Our checking was successful. We can protect the grid, switchgears and the superconducting wire effectively with this solution. We would like to contribute with this novel model solution to the development of an SFCL in industry because this technology is very simple and it can work safely.
Estimation of performance of Nb3Sn CICC with thermal strain distribution
Authors: Wesche R , Sedlak K , Bruzzone P
Published: June 2020

In the last few years, the critical temperature (T
c) of several ITER cable-in-conduit conductors (CICC) was determined by magnetization measurements at zero current. The distribution of the critical temperatures (T
c), caused by variation of strain in the Nb3Sn strands, was found to vary with the number of load cycles. A comparison with mechanical modelling requires the strain distribution, while the T
c distribution is sufficient to determine the CICC performance. The current sharing temperature (T
cs) is calculated supposing that the measured distribution of T
c is representative of its variation along a single strand and that the current is uniformly distributed among the strands. The T
cs values, found for background and peak magnetic field, are compared with the results of the DC test in the SULTAN facility. The presented estimation techniques lead to an overestimation of T
cs. The differences of the estimated and measured T
cs values are discussed including the effect of different current-voltage characteristics of single strands and CIC conductors.
Topology optimization for superconducting magnet system in helical fusion reactor
Authors: Tamura H , Goto T , Miyazawa J , Tanaka T , Yanagi N
Published: June 2020

In magnetic-confinement-type fusion reactors, the strong electromagnetic force generated by the superconducting coil is of the order of several tens of MN/m. To support this huge force, a strong and heavy coil support structure is required. The total weight of each magnet designed for conventional fusion reactors or experimental devices is several times greater than the ideal value. In recent years, structural optimization has advanced, owing to improvements in computer-aided design and finite-element analysis. For instance, the topology optimization method contributes novel designs that overturn common sense. In the present study, topology optimization is applied to the design of the magnet system used in a helical fusion reactor to reduce the weight of the magnet while maintaining the mechanical soundness of the component. A weight reduction of more than 25% from the conventional design could be achieved.
Development of the quench protection system for the CFETR CS model coil
Authors: Ma Y Y , Wu Y , Xu L W , Wu Y N , Li J , Mao H F
Published: June 2020

The Central Solenoid (CS) model coil, which is responsible for developing and verifying the larger-scale superconducting magnet technology of China Fusion Engineering Test Reactor (CFETR), has been designed and is currently being manufactured at ASIPP. The energy storage of the CS model coil is 407MJ, so a reliable quench protection system is needed to ensure the safety of the coil when a quench occurs. This paper describes the progress of the quench protection system. The two-stage commutating current technique is used to solve the difficulties that the breaker cannot directly break the high DC current. For the key components in the circuit, the prototype of the breaker was manufactured and the performance test was carried out. The engineering design and manufacture of the discharge resistor were carried out. An experimental study of the quench protection circuit was carried out to verify the feasibility of the design. Besides, the reliability of the quench protection control system is qualitatively analyzed based on the fault tree.
Investigation of trade-off solution in mechanical edge joint of STARS conductors
Authors: Sato S , Ito S , Hashizume H
Published: June 2020

Mechanical edge joints of stacked tapes assembled in rigid structure (STARS) conductors have been proposed to be applied to remountable high-temperature superconducting fusion magnets. Our previous study showed the joint resistance decreases with an increase in stabilizer thickness and joint pressure. However, this induces a trade-off between joint resistance and critical current due to increasing strain in the REBCO tape during bending (winding) for the conductors. Furthermore, an appropriate joint surface structure has not been discussed about taking into account a remountable joint. Based on the above background, this study first numerically evaluated the joint resistance depending on the structure of REBCO conductors with copper jackets. The results showed the copper jacket does not efficiently decrease the joint resistance compared to a copper stabilizer. Furthermore, to make strains lower than irreversible strain limit, the joint length should be longer than 500 mm. In addition, the joint surface structure was investigated based on joint testing and observing the surface, from which it was proposed that protective layer on the joint surface is needed to remove the remaining indium and keep the flatness of the joint surface. Therefore, a new structure for the issue was proposed for a remountable joint and the reattaching performance was evaluated experimentally.
Development of an inductive noise cancellation method for quench detection of the KSTAR CS coils by introducing improved plasma modeling
Authors: Kim Jinsub , Jeon Youngmu , Yonekawa Hirofumi , Kim Kwang-pyo , Chu Yong
Published: June 2020

An inductive noise cancellation method, CDA+MIK, has been developed for better performance of KSTAR (Korea Superconducting Tokamak Advanced Research) CS (Central Solenoid) coils’ quench detection. The CDA+MIK method was evaluated in real operations of the KSTAR superconducting coils. An analysis of this evaluation considering mutual inductances only among CS and PF (Poloidal Filed) coils showed insufficient reduction of the inductive noise in the quench detection signal. On the other hand a supplementary analysis taking into account of eddy currents induced on conductive structures and dynamic plasma evolutions capable to induce voltages showed better reduction even though the inductive noise was under-estimated. This paper describes an improved plasma modelling by considering plasma’s volume and shape, and also application of the model to the experimental results