Showing papers in "IEEE Transactions on Applied Superconductivity in 2015"

Analyses of Transient Behaviors of No-Insulation REBCO Pancake Coils During Sudden Discharging and Overcurrent

Abstract: Stability margin of a high-temperature superconducting (HTS) coil is two or three orders of magnitude greater than that of a low-temperature superconducting coil. In recent years, many papers have reported test results of turn-to-turn no-insulation (NI) HTS coils having extremely enhanced thermal stability, such that burnout never occurs in an NI coil, even at an operating current exceeding 2.5 times the critical current. Thus, The main goal of this paper is to clarify transient electromagnetic and thermal behaviors and mechanism of the high thermal stability in an NI REBCO coil. A partial element equivalent circuit (PEEC) model is proposed for the numerical simulation of an NI REBCO coil, which considers a local electrical contact resistance between turns, an I-V characteristic of an REBCO tape, and local self and mutual inductances of the NI REBCO coil. Using the PEEC model, we investigate the influence of the turn-to-turn contact resistance on the transient behavior of the NI REBCO coil during sudden discharging. We also perform thermal conduction analyses with the PEEC model to clarify the transient behavior of an NI REBCO coil during an overcurrent operation.

Cryogenic Computing Complexity Program: Phase 1 Introduction

Abstract: The ultimate goal of the Intelligence Advanced Research Projects Activity (IARPA)'s Cryogenic Computing Complexity (C3) program is to demonstrate a complete superconducting computer including processing units and cryogenic memory. IARPA expects that the C3 program will be a five-year two-phase program. Phase one, which encompasses the first three years, primarily serves to develop the technologies that are required to separately demonstrate a small superconducting processor and memory units. Phase two, which is for the final two years, will integrate those new technologies into a small-scale working model of a superconducting computer. Program goals are presented, and the approaches of the phase-one teams are reviewed.

The EuCARD-2 Future Magnets European Collaboration for Accelerator-Quality HTS Magnets

Abstract: EuCARD-2 is a project supported by FP7-European Commission that includes, inter alia, a work-package (WP10) called “Future Magnets.” This project is part of the long term development that CERN is launching to explore magnet technology at 16 T to 20 T dipole operating field, within the scope of a study on Future Circular Colliders. The EuCARD2 collaboration is closely liaising with similar programs for high field accelerator magnets in the USA and Japan. The main focus of EuCARD2 WP10 is the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, The cable will be used to wind a stand-alone magnet 500 mm long and with an aperture of 40 mm. This magnet should yield 5 T, when stand-alone, and will enable to reach a 15 to 18 T dipole field by placing it in a large bore background dipole of 12-15 T. REBCO based Roebel cables is the baseline. Various magnet configurations with HTS tapes are under investigation and also use of Bi-2212 round wire based cables is considered. The paper presents the structure of the collaboration and describes the main choices made in the first year of the program, which has a breadth of five to six years of which four are covered by the FP7 frame

Fabrication Process and Properties of Fully-Planarized Deep-Submicron Nb/Al– $\hbox{AlO}_{\rm x}\hbox{/Nb} $ Josephson Junctions for VLSI Circuits

Abstract: A fabrication process for Nb/Al-AlO x /Nb Josephson junctions (JJs) with sizes down to 200 nm has been developed on a 200-mm-wafer tool set typical for CMOS foundry. This process is the core of several nodes of a roadmap for fully-planarized fabrication processes for superconductor integrated circuits with 4, 8, and 10 niobium layers developed at MIT Lincoln Laboratory. The process utilizes 248 nm photolithography, anodization, high-density plasma etching, and chemical mechanical polishing (CMP) for planarization of SiO 2 interlayer dielectric. JJ electric properties and statistics such as on-chip and wafer spreads of critical current, I c , normal-state conductance, G N , and run-to-run reproducibility have been measured on 200-mm wafers over a broad range of JJ diameters from 200 nm to 1500 nm and critical current densities, J c , from 10 kA/cm 2 to 50 kA/cm 2 where the JJs become self-shunted. Diffraction-limited photolithography of JJs is discussed. A relationship between JJ mask size, JJ size on wafer, and the minimum printable size for coherent and partially coherent illumination has been worked out. The G N and I c spreads obtained have been found to be mainly caused by variations of the JJ areas and agree with the model accounting for an enhancement of mask errors near the diffraction-limited minimum printable size of JJs. I c and G N spreads from 0.8% to 3% have been obtained for JJs with sizes from 1500 nm down to 500 nm. The spreads increase to about 8% for 200-nm JJs. Prospects for circuit densities > 10 6 JJ/cm 2 and 193-nm photolithography for JJ definition are discussed.

A Full Scale Superconducting Magnetic Levitation (MagLev) Vehicle Operational Line

Abstract: This paper describes the construction and main components of a full-scale superconducting magnetic levitation vehicle. The prototype, comprising four 1.5-m-long wagons, will travel a short test line of 200 meters, connecting two buildings inside the campus of the Federal University of Rio de Janeiro. The efforts to implement this technology started thirteen years ago with a small-scale prototype in an attempt to prove the concept. The second step was the construction of a functional prototype that could levitate more than one Ton. The actual stage of this project is the construction of an operational prototype mentioned above, designed to transport up to 24 passengers. This work has been reported in several previous editions of the ASC conference. New details about the elevated test line, the permanent magnetic (Nd-Fe-B) guideways, the cryostats with YBCO high critical temperature superconductors, the energy conditioning, the linear induction motor and its regenerative braking, as well as the automatic supply system of liquid nitrogen will be presented in the proposed paper. Tests with this operational prototype demonstrate the technology feasibility.

A High-Resolution 1.3-GHz/54-mm LTS/HTS NMR Magnet

Abstract: A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting (HTS) nuclear magnetic resonance magnet (1.3 G) is currently in the final stage at the Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. Its key component is a three-coil (Coils 1-3) 800-MHz HTS insert comprising 96 no-insulation (NI) double-pancake coils, each wound with a 6-mm-wide GdBCO tape. In this paper, after describing the overall 1.3-G system, we present innovative design features incorporated in 1.3 G: 1) an NI winding technique applied to Coils 1-3 and its adverse effect in the form of charging time delay; 2) persistent-mode HTS shims; 3) a “shaking” magnet; and 4) preliminary results of Coil 1 operated at 4.2 K.

A Novel Model of HVDC Hybrid-Type Superconducting Circuit Breaker and Its Performance Analysis for Limiting and Breaking DC Fault Currents

Abstract: The key obstacle in integrating high-voltage direct current (HVDC) point-to-point networks into meshed multiterminal HVDC networks (MTDC) is the absence of dc circuit breakers (DCCBs), which can timely and reliably isolate the faulty HVDC network from the MTDC. In this paper, a novel hybrid-type superconducting DCCB model (SDCCB) is proposed. The SDCCB has a superconducting fault current limiter (SFCL) located in the main line, to limit the fault current until the final trip signal to the SDCCB is given. After the trip signal, insulated-gate bipolar transistor (IGBT) switches located in the main line will commutate the fault current into a parallel line, where dc current is forced to zero by combination of IGBTs and surge arresters. DC fault current behavior in MTDC and fundamental requirements of DCCB for MTDC were described, followed by an explanation of the working principles of the SDCCB. To prove the viability of the SDCCB, a simulation analysis demonstrating SDCCB current interruption performance was done for changing the intensity of dc fault current. It was observed that the passive current limiting by SFCL caused significant reduction in fault current interruption stress for SDCCB. Furthermore, fundamental design requirements for SFCL, including the effect of SFCL quenching impedance on SFCL voltage rating and energy dissipation capacity, were investigated. Finally, advantages and limitations of the SDCCB were highlighted.

Targets for R&D on Nb 3 Sn Conductor for High Energy Physics

Abstract: High Energy Physics has been consistently pushing the performance of technical superconductors, for the benefit of high field magnet technology. So far the workhorse for particle accelerators has been Nb-Ti, but the practical performance limit has been attained with the LHC. Calls for higher beam luminosity (e.g., HL-LHC), and higher beam energy (e.g., FCC), demand a transition from Nb-Ti to Nb3Sn, presently the only practical candidate material offering the required high field performance. This paper provides a summary of desirable properties and performance targets for Nb3Sn to satisfy the challenging magnet specifications for upgrades of existing and future HEP accelerators.

Transient Performance Improvement of Microgrid by a Resistive Superconducting Fault Current Limiter

Abstract: In this paper, a resistive-type superconducting fault current limiter (SFCL) is suggested to improve the transient performance of a microgrid system during a fault. The microgrid is connected to the main network at the point of common coupling, where the resistive-type SFCL is applied. When a short-circuit fault happens at the connecting line, the SFCL can mitigate the fault current, and its action signal will be sent to the master distributed generation (DG) included in the microgrid. Accordingly, the switching between the master DG's two control patterns can be flexibly performed; furthermore the microgrid system is expected to achieve a smooth transition between its grid-connected and islanded modes. Theoretical analysis and a technical discussion are conducted, and the simulation model of a typical microgrid with the SFCL is built in MATLAB. From the demonstrated results, employing the resistive-type SFCL can effectively limit the transient fault current to a lower level, help guarantee the microgrid system's power balance, and enhance its voltage and frequency stability.

HTS Electrical System for a Distributed Propulsion Aircraft

Abstract: As the commercial aircraft industry aims to meet the challenge of 2050 emissions targets, it becomes apparent that unconventional aircraft configurations may be necessary to achieve them. Distributed electrical propulsion offers opportunities for improving aircraft efficiency. However, the conversion and transfer of power could prove prohibitive when using conventional machines and conductors due to weight and inefficiency. An aircraft with distributed propulsion and boundary layer ingestion is considered in this paper, and the current view of the future of high-temperature superconductor technology as applied to aircraft is explained.

Towards a 1 V Josephson Arbitrary Waveform Synthesizer

Abstract: The establishment at PTB of an AC Josephson voltage standard (Josephson Arbitrary Waveform Synthesizer- JAWS) based on pulse-driven Josephson arrays is focused on achieving an output voltage of at least 1 Vrms which is required for many metrology applications In this paper, we approached this goal by increasing the number of active junctions in two ways Firstly, we fabricated arrays containing triple-stacked SNS-type Josephson junctions with Nb x Si 1-x as barrier material We obtained current operation margins of about 02 mA with arrays of up to 9000 Josephson junctions at an rms voltage of 355 mV Secondly, we used a new 8-channel ternary pulse pattern generator (PPG) to bias up to 8 arrays connected in series An output voltage of V RMS = 1006 mV(V PP = 2845 V) was achieved by using 8 arrays (arranged on 4 separate chips) with 63000 junctions in total Higher harmonics are suppressed by at least -116 dBc The fabrication process and the experimental setup will be described, as well as experimental results that are leading towards our 1 V goal

Accelerator-Quality HTS Dipole Magnet Demonstrator Designs for the EuCARD-2 5-T 40-mm Clear Aperture Magnet

Abstract: Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The Enhanced European Coordination for Accelerator Research and Development (EuCARD-2) Work Package 10 is a collaborative push to take high-temperature superconductor (HTS) materials into an accelerator-quality demonstrator magnet. The demonstrator will produce 5 T stand alone and between 17 and 20 T when inserted into the 100-mm aperture of a Fresca-2 high-field outsert magnet. The HTS magnet will demonstrate the field strength and the field quality that can be achieved. An effective quench detection and protection system will have to be developed to operate with the HTS superconducting materials. This paper presents a ReBCO magnet design using a multistrand Roebel cable that develops a stand-alone field of 5 T in a 40-mm clear aperture and discusses the challenges associated with a good field quality using this type of material. A selection of magnet designs is presented as the result of the first phase of development.

Application of Small-Sized SMES in an EV Charging Station With DC Bus and PV System

Abstract: As small-sized superconducting magnetic energy storage (SMES) system is commercially available at present, the function and effect of a small-sized SMES in an EV charging station including photovoltaic (PV) generation system is studied in this paper, which provides a practical application of small-sized SMES. The comparison of three quick response energy storage systems including flywheel, capacitor (super-capacitor) and SMES is also presented to clarify the features of SMES. SMES, PV generation system, and EV battery are connected to a common dc bus with corresponding converters respectively. Voltage source converter (VSC) is used for grid-connection. With characteristic of quick power response, SMES is utilized to maintain the dc bus steady. During the long-term operation of EV charging station, an energy management strategy is designed to control the energy transfer among PV units, SMES, EV battery, and power grid. The EV charging station system is modeled in MATLAB/SIMULINK and simulation tests are carried out to verify the function and performance of SMES.

Fault Ride-Through Capability Enhancement of DFIG-Based Wind Turbine With a Flux-Coupling-Type SFCL Employed at Different Locations

Abstract: Doubly fed induction generators (DFIGs) have attracted a wide interest for wind power generation, but they suffer from high sensitivity to grid disturbances, particularly grid faults. In this paper, a modified flux-coupling-type superconducting fault current limiter (SFCL) is suggested to improve the fault ride-through (FRT) capability of DFIGs. The SFCL's structure and principle is first presented. Then, considering that the SFCL can be installed at a DFIG's different locations, its influence mechanism to the DFIG's FRT capability is analyzed, and some technical discussions on the design of the SFCL are carried out. Furthermore, the simulation model of a 1.5-MW/690-V DFIG integrated with the SFCL is built, and the performance analysis is conducted. From the results, introducing the SFCL can effectively limit the fault currents across the DFIG's stator and rotor sides, and when the stator side is selected as the installation site, the terminal-voltage sag can be also improved, which helps prevent the disconnection of the DFIG from the power grid.

Inductance of Circuit Structures for MIT LL Superconductor Electronics Fabrication Process With 8 Niobium Layers

Abstract: Inductance of superconducting thin-film inductors and structures with linewidth down to 250 nm has been experimentally evaluated. The inductors include various striplines and microstrips, their 90° bends and meanders, interlayer vias, etc., typically used in superconducting digital circuits. The circuits have been fabricated by a fully planarized process with 8 niobium layers, developed at MIT Lincoln Laboratory for very-large-scale superconducting integrated circuits. Excellent run-to-run reproducibility and inductance uniformity of better than 1% across 200-mm wafers have been found. It has been found that the inductance per unit length of stripline and microstrip line inductors continues to grow as the inductor linewidth is reduced deep into the submicron range to the widths comparable to the film thickness and magnetic field penetration depth. It is shown that the linewidth reduction does not lead to widening of the parameter spread due to diminishing sensitivity of the inductance to the linewidth and dielectric thickness. The experimental results were compared with numeric inductance extraction using commercial software and freeware, and a good agreement was found for 3-D inductance extractors. Methods of further miniaturization of circuit inductors for achieving circuit densities> 10 6 Josephson junctions per cm 2 are discussed.

Nb3Sn High Field Magnets for the High Luminosity LHC Upgrade Project

Abstract: The high luminosity upgrade of the Large Hadron Collider at CERN requires a new generation of high field superconducting magnets. High field large aperture quadrupoles (MQXF) are needed for the low-beta triplets close to the ATLAS and CMS detectors, and high field two-in-one dipoles (11-T dipoles) are needed to make room for additional collimation. The MQXF quadrupoles, with a field gradient of 140 T/m in 150 mm aperture, have a peak coil field of 12.1 T at nominal current. The 11-T dipoles, with an aperture of 60 mm, have a peak coil field of 11.6 T at nominal current. Both magnets require Nb 3 Sn conductor and are the first applications of this superconductor to actual accelerator magnets. Collaboration between the US LARP (LHC Accelerator Research Program) and CERN is developing the MQXF magnets, whereas the 11-T dipole magnets are being developed by CERN and Fermilab. This paper reviews the status of Nb 3 Sn technology for accelerator magnets, discusses its main challenges, and discusses how the MQXF and 11-T designs are addressing them.

DC Circuit Breaker Using Superconductor for Current Limiting

Abstract: The unavailability of high-capacity HVdc circuit breakers (CBs) is one of the key stoppers for building HVdc multiterminal networks. As the dc does not have a natural current zero, its interruption is very different. The objective of this paper is to propose a new type of dc CB (DCCB), including a current-limiting part and an interrupting part, which can interrupt a high short-circuit current. Experimental results show that the current-limiting part containing superconductor tapes and parallel resistance can limit the fault current from 20 to 1 or 2 kA very quickly within 1 ms. The interrupting part using the self-oscillation method can break this limited current. Therefore, this type of DCCB has the ability of interrupting a high short-circuit current.

Study on No-Insulation HTS Pancake Coils With Iron Core for Superconducting DC Induction Heaters

Abstract: This paper focuses on no-insulation (NI) HTS pancake coils with iron core for superconducting dc induction heaters. A superconducting coil without turn-to-turn insulation and its conventional counterpart with insulation are wound with YBCO-coated tapes. An iron core is built for a laboratory-scale dc induction heater. The electromagnetic characteristics of the two coils with the iron core are studied focusing on the charging and sudden-discharging processes at 77 K. Three variables are measured, i.e., current, terminal voltage, and magnetic field induced. The results show that NI coil with the iron core incurs a significant delay in the charging and discharging process due to the influence of the iron core. A terminal voltage pulse is observed at the beginning of the sudden-discharging process, which is more than five times of its normal value. A circuit-field coupled method is proposed to analyze the electromagnetic characteristics of the NI coil with an iron core. The results from experiment and simulation exhibits good agreement. The research shows that it is possible to use the NI technique to build a HTS iron core magnet for a dc induction heater, which can simplify the quench protection system.

Resistive-Type Superconducting Fault Current Limiters: Concepts, Materials, and Numerical Modeling

Abstract: In recent years, major industrialized countries have begun to be concerned about the need for developing strategies on the integration and protection of the growing power capacity of renewable source energies, attracting back their interest on the development and understanding of superconducting fault current limiters (SFCLs). The reasons for this are simple: An SFCL may offer a rapid, reliable, and effective current limitation, with zero impedance during normal operation, and an automatic recovery after the fault. Nowadays, most of the R&D projects have turned toward the study of resistive-type SFCLs due to their potential to be small and the likely decrease in price of 2G coated conductors. Thus, in this paper, we provide an updated review on the state of the art of resistive-type SFCLs, emphasizing on the different approaches for the numerical modeling of their local physical properties, as well as on the already-tested experimental concepts. Comparison between the properties and characteristics of different resistive-type SFCLs using different superconducting materials is presented.

Detection Mechanism in SNSPD: Numerical Results of a Conceptually Simple, Yet Powerful Detection Model

Abstract: In a recent publication we have proposed a numerical model that describes the detection process of optical photons in superconducting nanowire single-photon detectors (SNSPD). Here, we review this model and present a significant improvement that allows us to calculate more accurate current distributions for the inhomogeneous quasi-particle densities occurring after photon absorption. With this new algorithm we explore the detector response in standard NbN SNSPD for photons absorbed off-center and for 2-photon processes. We also discuss the outstanding performance of SNSPD based on WSi. Our numerical results indicate a different detection mechanism in WSi than in NbN or similar materials.

One-Volt Josephson Arbitrary Waveform Synthesizer

Abstract: A quantum-accurate waveform with an rms output amplitude of 1 V has been synthesized for the first time. This fourfold increase in voltage over previous systems was achieved through developments and improvements in bias electronics, pulse-bias techniques, Josephson junction array circuit fabrication, and packaging. A recently described ac-coupled bipolar pulse-bias technique was used to bias a superconducting integrated circuit with 25 600 junctions, which are equally divided into four series-connected arrays, into the second quantum state. We describe these advancements and present the measured 1 V spectra for 2 Hz and 10 Hz sine waves that remained quantized over a 0.4 mA current range. We also demonstrate a 2 kHz sine wave produced with another bias technique that requires no compensation current and remains quantized at an rms voltage of 128 mV over a 1 mA current range. Increasing the clock frequency to 19 GHz also allowed us to achieve a maximum rms output voltage for a single array of 330 mV.

Resistive Superconducting Fault Current Limiters Are Becoming a Mature Technology

Abstract: Resistive superconducting fault current limiters (rSFCL) are reliably reacting devices and excellent means to overcome issues of higher short circuit current levels resulting from added electricity generation and more interconnected networks. Due to the strong impedance increase of the superconductor components initiated by a fault and the very low reactance under all operating conditions the rSFCL technology is ideal for protection of electricity grids. Several rSFCL systems based on different superconductor materials have been designed, built, tested, and commissioned by Nexans SuperConductors at distribution grids of several DNOs and also two times at a power plant. A recently built system is operating together with a HTS cable to supply up to 40 MVA on 10 kV enabling a very compact cable design. First market opportunities for medium voltage SFCLs have been identified and fully commercial projects targeting at permanent installations are now becoming reality. Different development stages leading from first trial devices to real commercial systems are presented including further necessary steps for SFCLs getting close to serial production.

Development of a 3 phi-66/6.9 kV-2 MVA REBCO Superconducting Transformer

Abstract: We have designed and fabricated a 3Φ-66 kV/6.9 kV2 MVA transformer with RE1Ba2Cu3O7-δ(REBCO, RE:Rare Earth, Y, Gd etc.) superconducting tapes. It is a 1/10 model of a 3Φ-66 kV/6.9 kV-20 MVA one for a distribution power grid. The superconducting windings were reduced only in current capacity by reducing the number of tapes in parallel conductors. In the primary side, a single REBCO tape with a width of 5 mm was cylindrically wound into 8 layers. In the secondary one, an 8-strand parallel conductor was wound similarly into 2 layers, where each strand was transposed 15 times per one layer. The REBCO tapes for the secondary winding were also scribed by laser into a 3-filament structure to reduce the ac loss. The windings for 3 phases were installed into a GFRP cryostat which had an elliptic-cylinder-shape and three cylindroid bore for an iron core at room-temperature. A Ne turbo-Brayton refrigerator with a cooling capacity of 2 kW at 65 K was developed and located close to the transformer. The windings were cooled with subcooled liquid nitrogen at 65 to 70 K, which was forced-flowed by a pump unit between the transformer and the refrigerator. The completed transformer was first tested in liquid nitrogen at 77 K according to the domestic regulation for conventional transformers. The load loss, i.e., ac loss of the windings, was 26.9 W for the rated operation. The dielectric strength was also verified by applying 350 kV impulse voltage and 140 kV ac voltage for 1 minute.

Linear Flux Pump Device Applied to High Temperature Superconducting (HTS) Magnets

Abstract: This paper presents a novel linear flux pump which could be used to magnetize 2G HTS tapes and coils. The design is based on an iron magnetic circuit together with copper solenoids and is powered by a current source driver circuit. Several applied waveforms were tested including a symmetric sine wave and an asymmetric trapezoidal wave. Both standing and travelling waves were applied. The measurements focused on the effects of frequency and magnitude of the applied field and their effect on the system pumping efficiency. It was found that a trapezoidal wave was more effective than a sine wave, producing a greater final current at the same applied frequency and field strength. The maximum induced current in the superconducting coil was 19 A which was achieved using an applied field of 50 mT, applied as a travelling trapezoidal wave. The driving current to the copper coils was 5 A in amplitude with a frequency of 10 Hz. It was found that when the applied field magnitude was less than 16 mT pumping did not occur. It proved possible to pump the system with a standing wave as well as a travelling wave. This effect needs to be investigated further as it is possible that the standing wave had travelling components.

Simulating the In-Field AC and DC Performance of High-Temperature Superconducting Coils

Abstract: In this paper, the authors investigate numerically the in-field behavior of high-temperature superconducting (HTS) coils and a method to potentially improve their performance using ferromagnetic material as a flux diverter. The ability to accurately predict the electromagnetic behavior of superconductors in complex geometries and electromagnetic environments is crucial to the design of commercially viable superconductor-based electrical devices, such as power transmission cables, superconducting fault current limiters, transformers, and motors and generators. The analysis is carried out using a 2-D axisymmetric model of a circular pancake coil based on the H-formulation and implemented in Comsol Multiphysics 4.3a. We explore the use of flux diverters to improve an HTS coil's performance with respect to its dc (maximum allowable/critical current) and ac (ac loss) characteristics, for various background magnetic fields. It is found that while flux diverters can improve the ac properties of coils, they can be detrimental to the dc properties in this particular configuration.

Concept and Design of 500 Meter and 1000 Meter DC Superconducting Power Cables in Ishikari, Japan

Abstract: The design and construction of two DC superconducting power cables were started in the spring of 2013 as a national project in Japan. The cable lengths are 500 and 1000 m, respectively. The project is called the Ishikari Project. Four parties, Chiyoda Corp., Sumitomo Electric, Sakura Internet, and Chubu University joined to establish a partnership. The 500-m cable will connect an Internet data center (iDC) to a large scale array of photovoltaic cells to supply dc power. During the design and the construction in the field, test benches have also been constructed to investigate the performance of the individual components of the cable system. The design value of the heat leak of the cryogenic pipe is 1.3 W/m and the experimental result is 0.7 W/m to 1.3 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. Control of the thermal contraction and expansion are important to maintain cable safety and two methods are considered. Construction was started in the field in mid-May, and the 500-m cable will be completed at the end of the fiscal year 2014.

Construction and Test of 7-T/68-mm Cold-Bore Multiwidth No-Insulation GdBCO Magnet

Abstract: As a sequel to our previous report on the key concept of the multiwidth (MW) no-insulation (NI) winding technique that applies the NI technique to a magnet assembly of double-pancake (DP) coils wound with varying tape widths (thus MW), this paper presents construction and test results of a 7-T/68-mm cold-bore MW-NI GdBCO magnet. A total of 13 DP coils were fabricated: five central DP coils were wound with 4.1-mm wide tape, while each of the remaining four pairs of DP coils, axially symmetric to the midplane, was wound, from center to end, with 5.1-, 6.1-, 7.1-, and 8.1-mm wide tapes. Each DP coil was tested in a bath of liquid nitrogen (LN2) at 77 K, to obtain its critical current and characteristic resistance. After stacking, the 13-DP magnet was tested in LN2 at 77 K. The key focuses of this paper are: 1) winding and testing of MW-NI DP coils; 2) DP–DP joints; 3) charging response of the magnet; 4) spatial field distribution; and 5) self-protecting feature in overcurrent operation.

Characteristics of REBCO Coated Conductors for 25 T Cryogen-Free Superconducting Magnet

Abstract: A 25 T cryogen-free superconducting magnet is under development at the High Field Laboratory for Superconducting Materials (HFLSM), Institute for Materials Research (IMR), Tohoku University. Fujikura has manufactured and supplied REBCO coated conductors for the 25 T cryogen-free superconducting magnet. In-field critical current (I c ) properties in high magnetic fields at lower temperatures below 20 K and mechanical properties are important for design of these superconducting magnets. However, there is insufficient data of I c properties in high magnetic fields above 15 T. In this work, in-field I c properties at 20 K, 15 T of several samples cut from commercial coated conductors are evaluated at HFLSM, IMR, Tohoku University. The correlations between I c at 20 K, 15 T and I c at 77.3 K are compared. As a result, it is confirmed that I c at 20 K, 15 T have a stronger correlation with in-field I c at 77.3 K rather than I c at 77.3 K, self-field. In addition, tensile strengths at 77.3 K of more than 30 samples of coated conductors are also evaluated.

Pulsed-Field Magnetization of Superconducting Tape Stacks for Motor Applications

Abstract: The potential of (RE)BCO superconducting bulks in rotating machine designs has been explored through numerous experimental prototypes, with the bulks being magnetized to act as held poles. However, stacks of superconducting tapes have emerged as a promising alternative for trapped held magnets partly because of their suitability for the pulsed-field method of magnetization, which is considered the most practical method of trapping flux. The benefits of using a stack of tapes as rotor held poles suitable for motors are reported. The ability to have a long rectangular stack allows for motor designs with more efficient held poles in terms of the flux produced per unit area of the pole and easy scalability. Such a rectangular stack was experimentally magnetized for the first time using a race-track-shaped pulsed-held coil giving a highly uniform and well-defined trapped held. The unique self-supporting 120 mm by 12 mm stack was produced by compressing a high-temperature-superconducting tape coated with a thin layer of solder. Shorter rectangular stacks were pulse magnetized over a temperature range of 10-77 K using a fully automated pulsed magnetization system.

Full-Gate Verification of Superconducting Integrated Circuit Layouts With InductEx

Abstract: At present, superconducting integrated circuit layouts are verified through a variety of techniques. A layout-versus-schematic method implemented in Cadence allows extraction of circuit schematics with certain geometry-dependent parameters. Lmeter calculates inductance in a layout network and, with proper setup, may also calculate resistance separately. Recently, InductEx was introduced to calculate multiterminal network inductance in a superconductor structure with support for more complicated 3-D geometries. Here, we present an improvement to InductEx that allows resistance, inductance, and Josephson junction critical current extraction of a full superconducting digital logic gate or cell in a single execution, as well as in reasonable time. We show how InductEx was designed to operate on tape-out ready layouts and, through example, how it is used for full-gate layout verification of contemporary logic cells.