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DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [ABSTRACT FROM AUTHOR]

This paper studies the current limiting behavior based on an air-core high-temperature superconducting transformer (HTST) and a group of inductor–capacitor series resonant limiters. The air-core HTST is composed of four same double-pancake type high-temperature superconducting coils made up of Bi-2333/Ag tape, and both of primary and secondary windings include two series superconducting coils. It plays the roles of inductive fault current limiting and transformation impedance; in addition, the magnetic flux saturation can also be avoided. Meanwhile, the inductor and capacitor series with the secondary winding of the air-core HTST in series resonance state are the conventional devices. The influence of them on the circuit can almost be ignored, because they are in series resonant state in normal operation. While the fault current appeared in the primary circuit, it will be limited by the impedance of the air-core HTST and the inductor without quench (the inductor and capacitor would quit the series resonant state). According to the preliminary experiment carried out in our laboratory, this superconducting current limiting module can operate as expected, and its behavior is satisfactory. [ABSTRACT FROM AUTHOR]

Currently, HVDC is in the spotlight for long-distance transmission and power connection between countries. Among them, MMC-HVDC is a new conversion technology that can solve the problems of switching loss and harmonics. MMC consists of many submodules connected in series. And the one submodule is composed of IGBTs, Diode, and Capacitor. At the transient state, the charged capacitor is discharged and added to the fault current. It will generate tens of times the surge current during the delays all IGBTs turn-off. This causes semiconductor device destruction. To solve this problem, we applied SFCL with fast response characteristics to the MMC. The response speed of the resistive SFCL is faster than that of the MMC system protection device, which can effectively limit the capacitor discharge current before the protection device operates. In this paper, AC grid, MMC-HVDC, DC cable and SFCL were modeled using PSCAD/EMTDC. After that, we confirmed the capacitor discharge current, current limiting rate, and interruption characteristics through DC line short circuit failure simulation. As a result, SFCL effectively limits the capacitor discharge current and continuously lowers the level of the fault current. [ABSTRACT FROM AUTHOR]

The medium voltage direct current (MVDC) is a promising direction of future shipboard power system (SPS). However, one of the main limitations encountered in its development is the fault isolation of DC side. This paper reveals the evolution process of short-circuit fault in typical MVDC SPS through equivalent circuit and transient simulation. Based on the analysis of protection needs, a superconducting current-limiting switch (SCLS) topology is proposed, which includes one superconducting coupled coil and two DC circuit breakers (DCCBs). The models of SCLS is built on MATLAB/Simulink and the current limiting principle and current sharing principle of SCLS are verified. The results show that the SCLS has effective current limiting performance and fault clearing effect. [ABSTRACT FROM AUTHOR]

DC fault is one of the most important and critical challenges for stable operation of DC microgrids. Resistive type superconducting fault current limiter (R-SFCL) is an ideal protective solution to limit DC fault current. However, the effect of only using SFCL may further deteriorate the DC bus voltage stability. This paper first analyzes the effect of R-SFCL on DC microgrid under different operation modes and different fault locations, and then presents a coordinated control method of SMES-battery hybrid energy storage system (HESS) and SFCL in ground fault. This method can not only reduce the fault current level but also regulate the DC bus voltage. Finally, the comparative study is conducted in PSCAD/EMTDC, the feasibility and superiority of the proposed method is verified. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase ac power supply circuit that based on modified voltage-fed quasi-Z-source inverter topology; it suits to the light or the heavy load and is fit for the resistive, inductive, or capacitive load. The topology, operating principle, voltage gain, control method, and its realization by DSP are described in this paper. The feasibility and rationality of the system is verified by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Shunt capacitors are deployed for power factor correction (PFC) to reduce the load reactive power and to provide voltage support. Nonlinear loads, such as variable speed drives, can inject harmonics into the network. If the line impedance value produces a resonance with the PFC capacitor and the injected frequency coincides with the resonant frequency, an overvoltage is produced across the capacitor, which can lead to failure or explosion. To protect the PFC capacitor, a reactor can be connected in series with the PFC capacitor and tuned at the harmonic frequency of the system resonance. This paper proposes the use of a high temperature-superconducting reactor (HTSR) as the tuned reactor. The reactor will have an extremely high-quality factor (Q) compared to the normal reactor that can never be manufactured commercially with such a high Q. The performance of the HTSR reactor in terms of its ability to protect the capacitor from overvoltage and to reduce power losses has been investigated. The results are compared with those using the conventional (low Q) reactor and show that the HTSR can significantly improve filter performance and reduce power losses in the filter. [ABSTRACT FROM AUTHOR]

A capacitor made of high-temperature superconducting (HTS) electrode plates and a dielectric layer, or “HTS capacitor” for short, has the potential advantages of working with other HTS devices at 77 K and producing low conductive loss at high frequency. It may have a specific application to cryogenic systems at high frequency, such as superconducting wireless power transfer (SWPT) systems. Working with HTS resonant coil in an adiabatic container, the HTS capacitor can also reduce the heat leakage of the cooling system. Considering a lack of relevant experimental study at present, an HTS capacitor composed of YBCO (YBa2Cu3O7- $_x$) tapes and a polyimide layer is proposed in this paper and tested in an SWPT system. Its characteristics and influences on the SWPT system are presented in detail by theoretic analysis and experimental investigation. A comparative experiment is carried out between the fabricated HTS capacitor and other capacitors made from normal materials. Finally, it is confirmed experimentally that the HTS capacitor can have a high-quality factor, work with the HTS resonant coil normally at 77 K, and provide the SWPT system with a performance enhancement. [ABSTRACT FROM AUTHOR]

A highly efficient wireless power transfer (WPT) system is required in many applications to replace the conventional wired system. The high temperature superconducting (HTS) wires are examined in a WPT system to increase the power-transfer efficiency (PTE) as compared with the conventional copper/Litz conductor. The HTS conductors are naturally can produce higher amount of magnetic field with high induced voltage to the receiving coil. Moreover, the WPT systems are prone to misalignment, which can cause sudden variation in the induced voltage and lead to rapid damage of the resonant capacitors connected in the circuit. Hence, the protection or elimination of resonant capacitor is required to increase the longevity of WPT system, but both the adoptions will operate the system in nonresonance mode. The absence of resonance phenomena in the WPT system will drastically reduce the PTE and correspondingly the future commercialization. This paper proposes an open bifilar spiral coils based self-resonant WPT method without using resonant capacitors at both the sides. The mathematical modeling and circuit simulation of the proposed system is performed by designing the transmitter coil using HTS wire and the receiver with copper coil. The three-dimensional modeling and finite element simulation of the proposed system is performed to analyze the current density at different coupling distances between the coil. Furthermore, the experimental results show the PTE of 49.8% under critical coupling with the resonant frequency of 25 kHz. [ABSTRACT FROM AUTHOR]

Superconducting inductive pulsed power supplies have attracted a lot of attention due to its lower electrical loss and higher energy storage density than traditional inductors. To effectively improve charging rate and output continuous current pulses, a repetitive inductive pulsed power supply circuit topology based on high-temperature superconducting (HTS) pulsed power transformer was proposed and simulated in our previous studies. This paper aims to further study the feasibility of the repetitive inductive pulsed power supply circuit topology through experiments. A small air-core HTS pulsed power transformer and a bridge-type capacitor switching circuit were used to build the experimental platform. The experimental results show that the bridge-type capacitor switching circuit can shorten the charging time of each new cycle and the repetitive inductive pulsed power supply circuit is feasible for continuous current pulse output. [ABSTRACT FROM AUTHOR]

DC system protection is more challenging than that for AC system due to the rapid rate of rise of the fault current and absence of natural current zero-crossing in DC systems. Superconducting fault current limiter (SFCL) in DC systems is a promising technology to reduce the fault current level and the rate of rise of the fault current, and also SFCLs have no resistance during normal operation. In this paper, the behaviors of an SFCL coil are investigated under both low impedance and high impedance fault conditions in DC systems. In the low impedance fault condition system, the SFCL coil performs effective limitation of the fault current level under different prospective fault current levels. The application of SFCLs with limited inductance in the DC system can be a potential solution to effectively suppress the fault current under low impedance short-circuit faults. The SFCL coil under the high impedance fault condition can only limit the prospective fault current when it is much higher than the critical current of the coil. [ABSTRACT FROM AUTHOR]

As the output power of wind farm is fluctuating, it is one of the important ways to improve the schedule ability of wind power generation to predict the output power of wind farm. The operation mode of tracking planned output takes the planned value issued by the grid dispatching as the control basis of wind power generation. This operation mode is easy to control, which not only meets the needs of power grid dispatching, but also improves the reliability and controllability of new energy generation. This paper introduces the traditional PI control strategy of SMES and combines the advantages of SMES and the characteristics of application scenarios, and introduces sliding mode variable structure control into SMES. Through simulation and comparison of two different control modes, it is verified that SMES adopting sliding mode variable structure control have the advantages of fast response speed and strong robustness, which can make the wind farm output stable power according to the planned value. [ABSTRACT FROM AUTHOR]

A quasi-continuous high magnetic field is a special kind of pulsed magnetic field with a flat-top field longer than 100 ms. This paper proposes a hybrid power supply that consists of a capacitor power supply and a generator-rectifier power supply. A dual-coil magnet is powered to generate a 65 T/100 ms quasicontinuous high magnetic field with a ripple less than 500 ppm at the Wuhan National High Magnetic Field Center, Wuhan, China. A protection circuit consists of an R-C branch and a diode array is discussed for the worst short-circuit fault, which occurs between the first turns of inner coil and outer coil. This type of faultwill produce oscillation voltage with a high peak value and high frequency on the rectifiers. A self-adaptive PI controller with the coefficients corrected by a back propagation neural network is adopted to reduce the ripple of a flat-top. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose a dc current interruption technology for railway dc traction systems, consisting of a dc vacuum circuit breaker with a superconducting fault-current limiter (SFCL). To this end, a 1.5-kV dc circuit breaker prototype is designed, involving a dc vacuum circuit breaker and a resistive-type SFCL serially connected. The dc vacuum circuit breaker is developed with a commutation circuit to generate a reverse injection current, and the resistive-type SFCL is composed of yttrium barium copper oxide superconducting tape. An LC current source tested the 1.5-kV prototype, showing that, when the precharged capacitor voltage is 1.5 kV, the prospective current is 47 kA increasing at a rate of 9.4 A/μs. The SFCL limits this current to ~3 kA (peak value), and then, decreases the current to 2 kA after 6 ms, followed by successful clearance via the dc vacuum circuit breaker. The proposed 1.5-kV circuit breaker will successfully clear short-circuit faults up to 47 kA by first limiting the prospective current and then interrupting it. [ABSTRACT FROM AUTHOR]

Inductive pulsed power supply (IPPS) based on multiple high-temperature superconducting pulsed power transformer (HTSPPT) modules is a novel technology for electromagnetic launching. In a compact multimodule IPPS, the mutual couplings between HTSPPT modules are unavoidable. In this paper, an IPPS with the method of improved pulse-forming process which proved to be feasible by preliminary experiment is proposed to analyze the effect of the mutual couplings. The characteristics of the mutual coupling effect on the IPPS are presented in detail by theoretical analysis and parametric simulations. The evaluation indices reflecting performances of the IPPS under the mutual coupling effect are derived from simulations, including the energy storage capacity, flux linkage, axial tensile force, output current amplitude, and so on. Parametric simulations are executed with respect to the module arrangement, the number of modules, and the arrangement radius. Finally, the analysis of mutual coupling effect is summarized, and a strategy for exploiting mutual couplings between modules is put forward to improve IPPS performance. [ABSTRACT FROM PUBLISHER]

This paper proposes a new circuit topology for SMES (superconducting magnetic energy storage), which is based on a pulse link concept of two converters. A two quadrant dc chopper and a dc/ac converter connected via high frequency dc pulse link voltage. This concept has two advantages. All semi-conductor switches operate under soft-switching condition, which results in low loss generation and possibility to increase switching frequency. The other advantage is eliminating smoothing capacitor between two conversion stages. By these advantages, the proposed converter has possibility to achieve high efficiency and power density with rich controllability. This paper describes operation principles of the proposed converter. First experimental verification of this concept was conducted with small scale setup. [ABSTRACT FROM PUBLISHER]

For the future applications of high-temperature superconducting (HTS) cables in the smart grid with power line communication (PLC), it would be unavoidable for HTS cables to experience the PLC signals. For the normal cables experiencing PLC signals, line trap is a commonly used inserted device to block signals from radiating across other cables. With HTS cables working at low temperature, superconducting line trap (SLT) based on HTS coil and HTS electrode capacitor might play a role to achieve a desired transmission path of PLC signals across HTS cables. Since there still remains a research gap of SLT, a prototype is proposed in this paper and its characteristics are presented by principle analysis as well as experimental research. It is found that SLT can offer a higher blocking impedance to carrier signals and produce much smaller loss at power frequency than the line trap made from normal materials. [ABSTRACT FROM AUTHOR]

The objective of this paper is to evaluate the engineering feasibility of high-frequency magnet systems for the magnetic hyperthermia cancer therapy. For the effective induction heating properties of the magnetic particles with a short-time cancer therapy, the target specifications of the magnet system are 0.06 T of the peak magnetic field with 200 kHz of the operating frequency and with 300 s (5 minutes) of the continuous or intermittent operation time. From the results, the magnet designed using 200-A copper Litz wires and a magnetic core enables the reduction of one turn voltage of the coil windings to 8.47 kV. The winding loss is 3.89 kW, which suggests that the magnet can be operated without a water cooling system. Single voltage source high-frequency inverter using commercially available SiC-MOSFET (<1.2 kV) can drive the magnet with balancer circuits using variable series capacitors. [ABSTRACT FROM AUTHOR]

The superconducting dipole magnets of the Large Hadron Collider operate in a superfluid helium bath at 1.9 K. As a part of the magnet quench protection system, each dipole magnet is equipped with a bypass diode located in the helium bath. The connection between the superconducting magnet and the cold by-pass diode is made through a clamping system called "halfmoon," located at the lowest point of the cold-masses. This area is prone to receiving metallic debris residual from the assembly technological processes. The metallic debris might move and create an earth fault during helium flows that occur not only during the cool-down, warm-up, and flushing of the cryogenic installation but also during magnet quenches at high currents. In case of appearance, the earth fault is detected by the protection system of the circuit and as a consequence, the current is ramped down to zero. Subsequently, with the circuit current already at zero, the fault can be eliminated using a device denominated as the Earth Fault Burner. The fault elimination must follow a strict procedure as it is not fully risk-free. This paper describes the details of such earth fault elimination, including preliminary diagnostics and necessary hardware. Two examples from the LHC operation are described and discussed. [ABSTRACT FROM AUTHOR]

A repetitive pulsed high magnetic field is a useful tool for scientific research and industrial applications. In this paper, a novel repetitive pulsed power system (RPPS) adopted to generate repetitive pulsed high magnetic fields (RPHMF) at the Wuhan National High Magnetic Field Center (WHMFC) is designed. The capacitors serve as the energy storage elements in the pulsed power system, and the key issue of the RPHMF system is to decrease the loss and to charge the capacitors quickly, safely and efficiently. For this purpose, a new discharge topology is used to feed the energy stored in the magnet back to the capacitor by an additional choke coil and a resonant capacitor. The energy lost during each pulse will be replenished to the capacitor through a high frequency series-parallel resonant capacitor charging power supply (CCPS). [ABSTRACT FROM PUBLISHER]

The purpose of this paper is to propose the high-performance modulation strategy, power control and current regulation schemes for a multiple-channel current source converter (CSC) fed high temperature (HT) superconducting magnetic energy storage (SMES), which can in turn function as the frequency stabilizer and active power filter for the distributed generation system. The key is to design and implement the interleaved space vector modulation technique to suppress the switching harmonics, the dynamic capacitor voltage control to damp LC resonance as well as regulate grid currents accurately, and the DC current balancing strategy to avoid the circulating currents. The multiple-channel CSC fed HT SMES with the proposed control scheme is verified to provide good performance in power compensation and power quality improvement. [ABSTRACT FROM PUBLISHER]

This paper presents the design process and test results of a high-temperature superconducting pulsed-power transformer (HTSPPT). The primary winding of the HTSPPT is constructed out of several double-pancake-type coils connected in series. Every double-pancake-type coil is made of Bi2223/Ag tapes. The secondary winding is constructed out of several single-pancake-type coils made of normal conductors. The configuration of the HTSPPT is designed such that the primary and secondary coils are arranged in interleaving. The testing experiments show that a high-current impulse could be achieved with a small current in the primary, which proves that the designed test circuit and the configuration of HTSPPT are feasible. [ABSTRACT FROM AUTHOR]

A flux-lock type superconducting fault current limiter (SFCL) can change the amplitude of the magnetic field by adjusting either the inserting resistance or the phase adjusting capacitor. However, the magnetic field coil cannot generate enough magnetic field for some time after a fault happens due to resonance between the phase adjusting capacitor and the magnetic field coil. It is also required for the magnetic field generated to be controlled for the application to High-To superconducting (HTSC) elements which have different critical characteristics. This paper proposes a flux-lock type SFCL with a control circuit for the magnetic field, which is composed of solid state switches connected with the magnetic field coil. A current limiting experiment of this model was carried out. We showed that the amplitude of the fault current as well as the magnetic field could be controlled by the sinusoidal pulse width modulation (SPWM) operation, one of the switching techniques for controlling the magnetic field. [ABSTRACT FROM AUTHOR]

A bidirectional repeating long pulse magnet system for room temperature magnetic refrigerator has been designed in Wuhan National High Magnetic Field Center. By using ac power capacitor bank and anti-parallel thyristors, a bidirectional magnetic field is generated and the classical crowbar is removed for maximizing the utilization of energy. For the sake of long pulse width and repeating pulse application, a special rapid cooling magnet with large inductance of 87 mH and internal cooling channels is designed. It has a 60 mm bore and 16 layers, with 7 internal cooling channels built by annular sticks between layers. Finally, the proposed bidirectional repeating long pulse magnet system with bidirectional magnetic field of + 6.2\ \T/ -\hskip-2.65pt3.8\ \T and pulse width of 193 ms has been successfully achieved. The design and implementation of the proposed repeating pulsed magnet system will be presented in detail in the paper. [ABSTRACT FROM PUBLISHER]

This paper presents results of a study, experimental and computational, of a detect-and-activate-the-heater protection technique applied to a magnesium diboride (MgB2) test coil operated in semi-persistent mode. The test coil with a winding ID of 25 cm and wound with \sim500-m long reacted MgB2 wire was operated at 4.2 K immersed in a bath of liquid helium. In this active technique, upon the initiation of a “hot spot” of a length \sim10 cm, induced by a “quench heater,” a “protection heater” (PH) of \sim600-cm long planted within the test coil is activated. The normal zone created by the PH is large enough to absorb the test coil's entire initial stored energy and still keeps the peak temperature within the winding below \sim260 K. [ABSTRACT FROM AUTHOR]

Coils for pulsed magnets in the range of 50-75 T are developed with optimized combinations of conductors and reinforcement for the prototype laboratory of the Wuhan High Magnetic Field Center (WHMFC). The basic design tool is a Pulsed Magnet Design Software package (PMDS) for calculating the capacitor discharge, conductor heating, mechanical stresses and the residual stress, including plastic deformation and winding tension. A 1 MJ capacitor bank is equipped with a thyristor switch, a mechanical switch, polarity reversal switches, a current limiting inductor and a diode crowbar. The design and the test results of the magnets, of the protection inductance and of the capacitor bank are presented and discussed in this paper. [ABSTRACT FROM AUTHOR]

Three small pulsed high magnet field devices (SPHMF) which can continuously operate 20 times in rated power with different maximum magnetic field intensity from 10 T~40 T were developed in Wuhan High Magnet Field Center(WHMFC). The SPHMF systems are used to investigate the sterilization of fruit juice, magnetization of permanent magnet for wind power generator, some industrial applications and so on. The SPHMF consists of pulsed capacitor power supply, charger, control & measurement system, cryogenic system and pulsed magnet. These systems can accommodate sample room size from Φ 12 mm to Φ 18 mm and hold sample room in indoor temperature 300 K for different scientific researches and high magnetic field industrial applications. In this paper, power supply, magnet, control system and cryogenic system are presented. The total experiment results of SPHMF show that the devices are feasible, steady and reliable. [ABSTRACT FROM AUTHOR]

A new Pulsed High Magnetic Field Facility (PHMFF) is under construction at the Huazhong University of Science and Technology (HUST) in Wuhan, China. In order to provide a wide spectrum range, a modular capacitive pulsed power supply is designed to energize 12.5 MJ at 25 kV and a large variety of coils are designed for magnetic fields in the 50-80 T with pulse duration 15-200 ms, respectively. In order to energize multi-coil systems, the 12.5 MJ power supply is divided into 11 independent 1 MJ modules with a short circuit current of 44.7 kA each and 2 independent 0.75 MJ modules for 61.2 kA each. Each module is provided with its own protection inductor, thyristor switch, crowbar circuit, dump circuit, polarity-changing circuit, charging unit and switchgear. The current pulses can be modified in shape, amplitude and duration by varying the charging voltage, the number of modules and the crowbar resistors. For verifying the design scheme and gaining experience in the construction and operation of pulsed power supply, a 1 MJ prototype that is used to energize pulsed magnets for 50-72 T fields with reversible polarity has been developed. In this paper, after the introduction of the system configuration with different module types and system settings, the design of both the 1 MJ and 0.75 MJ modules is described in detail. Finally, test results of the 1 MJ prototype are presented. [ABSTRACT FROM AUTHOR]

We have proposed a superconducting thin-film fault current limiter (FCL) that uses high-resistivity Au-Ag alloy shunt layers for the protection against "hot spots". Its design enables reduction of the total length of FCL elements that can withstand high electric fields E > 40 Vpeak /cm, thus greatly reducing the cost of FCLs. In this paper, two methods to increase current capacity of the FCLs were demonstrated. The first method protects the films from hot spots by using capacitors in addition to external resistors. The capacitors decrease rapid voltage rise in the films at the moment of quenching. The second method maximizes the rated current of two parallel-connected thin films by using parallel connections via superconducting tapes, even if the critical currents of these films are largely different. We then successfully tested 'two parallel-connected YBCO films prepared by a low-cost, metal organic deposition (MOD) method. Over-current tests showed that (a) superconducting transport currents up to 380 Apeak flowed 5 cycles without quenching, which is more than 1.3 times larger than the peak value of the 200 Arms rated current and (b) after switching, E = 45.7 Vpeak/cm was achieved without film degradation. [ABSTRACT FROM AUTHOR]

Multilayer superconducting quadrature hybrids for diplexer applications are reported for the first time in this paper. The hybrids employ highly miniature lumped element components embedded within four metal layers. The thin dielectric layers between the metal layers and the small feature size of the process allow for the miniaturization of lumped element capacitors and inductors. Hybrid-coupled diplexers using lumped element hybrids and filters have been developed, fabricated, and tested. A novel filter configuration that employs inter-resonator tap connections is also demonstrated for implementation in wideband filter applications. The whole integrated high Q (quality factor) diplexer is highly miniaturized being approximately λ[sub0] /60 in size at a frequency of 1.0 GHz. The diplexer structures are amenable to superconductor microelectronics technology and can be integrated monolithically with a superconducting receiver on a single chip. [ABSTRACT FROM AUTHOR]

A pulsed high magnetic field laboratory has been funded to be established at the Huazhong University of Science and Technology (HUST), Wuhan, China by the National Development and Reform Committee. The facility is planned to be open for external users in 2011 with the implementation of various experimental techniques in pulsed magnetic fields up to 80 T. Pulse durations are in the range from 15 to 1000 ms with the magnet bore sizes from 12 to 34 mm. The pulsed power supplies are a 12 MJ, 25 kV capacitor bank and a 100 MVA/100 MJ flywheel pulse generator. The design and analysis of the power supplies and the magnets of short and long pulse durations and the multi-stage pulsed magnets with controllable waveforms are presented in this paper. [ABSTRACT FROM AUTHOR]

ARMS is the acronym for Advanced Research Magnet Systems, a project under the European Union's 5th Framework Research Infrastructures program (HPRI-CT-1999-5007). Eight partners throughout Europe cooperated in ARMS, which was coordinated by the University of Oxford, UK. The objective of the project was to build an 80 T user magnet to be installed at LNCMP, Toulouse, France. The approach chosen was the coil-ex/coil-in method, whereby a large outer coil was energized by LNCMP's unique, 14 MJ capacitor bank. The inner coil was energized by a fast, 100 kJ bank at the peak of the outer coil's field. In this paper the evolution of the coils, the conductors and other materials is outlined as is the testing and ultimate, successful use in physics experiment up to 76 T. A view of the future direction of high pulsed fields in Europe, post-ARMS, will also be given. [ABSTRACT FROM AUTHOR]

Physical implementations of qubits can be extremely sensitive to environmental coupling, which can result in decoherence. While efforts are made for protection, coupling to the environment is necessary to measure and manipulate the state of the qubit. As such, the goal of having long qubit energy relaxation times is in competition with that of achieving high-fidelity qubit control and measurement. Here, we propose a method that integrates filtering techniques for preserving superconducting qubit lifetimes together with the dispersive coupling of the qubit to a microwave resonator for control and measurement. The result is a compact circuit that protects qubits from spontaneous loss to the environment, while also retaining the ability to perform fast, high-fidelity readout. Importantly, we show the device operates in a regime that is attainable with current experimental parameters and provide a specific example for superconducting qubits in circuit quantum electrodynamics. [ABSTRACT FROM PUBLISHER]

Thyristor converters are used as power conditioning systems for superconducting coils. The objective of this work is to discuss the series compensation of thyristor converters using variable series capacitors. Traditional thyristor converters operate with lagging power factor requiring large reactive compensation efforts. Similarly, the series capacitor can control the coil voltage through a unity power factor thyristor converter with a resulting leading power factor seen from the grid. Therefore, by combining the two, both leading and lagging reactive power control, and also the active power control of the superconducting coils can be achieved. In order to demonstrate the feasibility of the series compensation of the thyristor converter, a prototype converter using a gate-commuted series capacitor (GCSC) is developed. From the experimental results using a superconducting coil, the authors demonstrated the leading current control capability of the series compensated thyristor converter, and verified the leading, lagging, and unity power factor control capability based on thyristor converter systems. This feature leads to a potential reduction in reactive power compensation need of 50 percent of the conventional thyristor converter system. [ABSTRACT FROM PUBLISHER]

These days, voltage stability of power system is very important for example in semiconductor industries. So, development of a device suppressing voltage sags in power system is expected. In this article, the authors propose a new voltage stabilizing device using a LC resonance circuit composed of superconducting coil and capacitor connected in parallel. This power system voltage stabilizer acts automatically against a voltage sag or a steep voltage change, and it suppresses the voltage drop for several cycles by releasing its stored energy. The authors have confirmed this principle experimentally using a small model system using a LC resonance circuit with a superconducting coil and a capacitor. The experimental results and some theoretical analyses are presented. [ABSTRACT FROM AUTHOR]

The authors investigate the operational characteristics of a flux-lock-type high-Tc superconducting (HTSC) fault cur- rent limiter (SFCL) with a tap changer which could adjust the number of turns of the third winding. In the case of conventional flux-lock-type SFCL, the phase adjusting capacitor is connected in series with magnetic field coil to adjust the magnetic field applied to the HTSC element in phase with the current flowing through the HTSC element during a fault time. However, the current flowing at the third winding, which is connected with magnetic field coil, affects the fault current limiting characteristics. To analyze the influence of current flowing at the third winding on the fault current limiting characteristics, the fault current limiting characteristics of the flux-lock type SFCL, whose inductance of coil 3 could be adjustable through a tap changer, are investigated through the experiments and the computer-aided simulations. The relation of line currents flowing into the flux-lock-type SFCL during a fault time and numbers of turns of a tap changer is drawn. [ABSTRACT FROM AUTHOR]

Recent and future astronomical instruments are based on a focal plane mapped by a large array of superconducting bolometers. Cryogenic analog multiplexing readout techniques, based on superconducting quantum interference devices (SQUIDs), are currently developed to achieve the readout of large arrays of this kind of low noise background-limited detectors. To effectively reduce the number of cryogenic wires (particularly, SQUID biasing), line/column addressing is currently used in time-division multiplexing, i.e., same biasing is applied to a few SQUIDs (on a line) of different columns. This technique should dramatically increase power consumption if parallel biasing is applied via resistors to isolate each column; the power budget is particularly limited on this kind of front-end cryogenic readout. A design with one transformer per SQUID is also used to read out SQUID biased in series with no excess of consumption and crosstalk. We propose here a new biasing technique using simple surface-mounted capacitors, which is easier to implement. These capacitors are used to parallel bias SQUIDs without additional Joule effect while minimizing crosstalk. However, capacitors do not allow dc biasing and need a current mean value equal to zero to avoid biasing source saturation. We have then tested square current biasing through capacitors on a commercial SQUID. This measurement shows that capacitors are able to proper bias SQUID and then to perform a nondissipative addressing for time-division SQUID multiplexing. [ABSTRACT FROM AUTHOR]

Since the accomplishment of the pulsedmagnetic field facility at the Wuhan National High Magnetic Field Center in 2013, five 65 T monolithic-coil magnets have been developed and used for scientific research. As the workhorse, the 65 T user magnets show excellent cooling performance and long service life. These user magnets have typical bore size of 21 and 23 mm. For electrical transport measurements, the magnets are energized by a 2 or 3-MJ capacitor bankwith crowbar circuit for~40-70 ms pulse duration. For magnetization measurements, shorter pulse duration of 11 ms for a field waveform with almost symmetrical rising and falling edges can be obtained with a 1.25-MJ capacitor bank that allows high-voltage reversal. The cooling time between two 60 T pulses ranges from 30 to 50 min depending on the magnets and the field waveform. Up to now, three of these magnets failed after 916, 583, and 947 pulses with the magnetic field above 60 T. The other two have delivered 706 and 56 pulses above 60 T and are still in operation. [ABSTRACT FROM AUTHOR]

It is well known that the efficiency of a wireless power transfer (WPT) system depends on the resistance of the transmitting and receiving coils, especially for the case of low frequency. Since the ac loss of high temperature superconductors (HTS) is much lower than that of conventional conductors, using high temperature superconductors for WPT system is a good way to increase power transfer efficiency. Here, several kinds of WPT experiments were designed and conducted by use of HTS and conventional conductor (copper) coils, respectively. The results are presented and analyzed. It is shown that the behavior of HTS WPT system is similar to that of a conventional WPT system, but the efficiency of WPT system is much higher by use of HTS coils and HTS coil is more suitable for being as a transmitting coil than as a receiving one. [ABSTRACT FROM PUBLISHER]

Recently, a Program-controlled Synchronous Triggering System (PSTS) is developed at Wuhan National High Magnetic Field Center. The designed system could generate triggering signal for thirteen power modules and eight magnets distributed in different experiment stations. By generating precise and synchronous triggering signals required for the facility, the multiple power modules could be discharged synchronously or in a preset time sequence. The PSTS is composed of triggering signal generator, fiber converter, expanded cell, and local sequence generator. The triggering signal generator, isolated from local device, is applied for sequential control of multi-module in the facility. The signal transmission is realized by optical fiber. A Digital Signal Processor (DSP) with specific type of TMS320F2812 is employed to design the triggering signal generator. The parameters of triggering channels and time-delay with the accuracy of 1 us could be configured through human machine interface. Local sequence generator unit is integrated in the local control unit on the basis of a Complex Programmable Logic Device (CPLD) with specific type of EPM7128. Local sequence generator is responsible for producing the time sequence signals to control and record the waveform of each power module, as well as the triggering signal waveform modulation for thyristor through expanded cell. Based on the designed system, the pulsed high magnetic field facility could be operated effectively. The test result illustrates that the system is of high performance. [ABSTRACT FROM PUBLISHER]

The simulation model for a new power supply of the injection bump system magnets refid="ref1"/refid="ref2"/ refid="ref3"/refid="ref4"/ of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Complex) refid="ref5"/, refid="ref6"/ has been constructed. The new power supply requires the reduction of the ripple noise current which will resonate with load and excites a forced beam oscillation at \sim96 kHz in the injection stage. In order to incorporate the load impedance in the simulation model, the impedances of a feeder line and the bump magnet with a ceramic vacuum chamber refid="ref7"/ inside were measured. The RF shield is formed on the ceramic surface along the beam direction. The results were successfully analysed using the OPERA-3D refid="ref8"/ and the circuit simulation code, Micro-Cap refid="ref9"/, and showed a good agreement. It was found the RF shield of a ceramic chamber has a resonant structure corresponding to \sim96 kHz. [ABSTRACT FROM PUBLISHER]

A 35 kA thyristor DC switch which consists of 8 paralleled high power thyristors installed in a disc-shaped aluminum bus to get a symmetrical structure is developed in order to meet the requirement of the DC power supply using lead-acid batteries in pulsed magnetic field with maximum flat-top current 35 kA, pulse width 1 s. This thyristor DC switch will be turned on at the beginning of experiment, and turned off by forced commutation technology which uses charged capacitors to output inverse current to extinguish the current of thyristor switch at the end. Every branch of 8 thyristors is in series with a stainless steel resistor 1.4 m\Omega and a fast-fuse to achieve parallel current sharing and overload protection of the thyristors. [ABSTRACT FROM PUBLISHER]

A SMES (Superconducting Magnetic Energy Storage) is basically a pulse current source. It is an attractive power supply for electromagnetic launchers, which require pulse currents to launch items or projectiles at very high speeds. SMES brings an alternative to the capacitors used at present which requires a pulse forming inductance limiting the energy transfer efficiency. The resulting oversizing of the primary source is more the issue than the efficiency itself, as power capacitors do not show high mass/volume densities of energy. The very high current required by the launcher may be reached using the XRAM concept, which is a current multiplier for SMES. We will compare the performances of SMES and capacitors to supply a small and a large launcher for different scenarios such as a total or a partial discharge of the SMES. [ABSTRACT FROM PUBLISHER]

We designed and constructed a twin coil conduction-cooled HTS SMES (Superconducting Magnetic Energy Storage using High Temperature Superconductor) for pulse power operation and sequential discharge. The distance between the two coils and their respective inductances were calculated to obtain identical energy during sequential discharge. Both coils are designed for high voltage operation up to 4 kV. Moreover, the second coil is split in 3 to test the XRAM principle, which consists in charging inductances in series and discharging them in parallel to sum up their currents. The upper coil reached its rated current (250 A), it was tested up to 3 kV during fast discharge in a power capacitor. The lower coil, rated at 300 A, was tested in XRAM operation up to 200 A, the current output thus reaching 600 A. The characteristics of the demonstrator will be introduced; the experimental setting will then be presented along with the tests results. [ABSTRACT FROM AUTHOR]

We fabricated a dc SQUID phase qubit with a sub-\mum Al/AlOx/\rm Al qubit junction and an interdigitated shunting capacitor on a sapphire substrate. The qubit junction had a critical current of 135 nA, and the isolation junction had a critical current of 8.3 \muA. The shunting capacitance was about 1.5 pF. To reduce the unwanted effects of two-level systems and increase the relaxation time T1, we have removed unnecessary dielectrics, used a small qubit junction area (450 nm \times 500 nm), isolated the qubit from the leads with an on-chip LC filter, and fabricated the device on a bare sapphire substrate. However, at a temperature of 20 mK, we found T1\approx 300\ ns and the coherence time T2\approx 110\ ns, which was much lower than one would expect from loss attributed to the leads and to dielectrics in the tunnel junction and substrate. Measurements of T1 versus applied flux (which tuned the qubit frequency) revealed a correlation between the strength of the coupling of the microwave excitation line to the qubit and the rate of energy dissipation in the qubit. This result suggests that the relaxation time was being limited by coupling to the microwave line. [ABSTRACT FROM AUTHOR]

We present an experimental investigation of lumped-element superconducting LC resonators designed to provide different types of coupling to a transmission line. We have designed four resonator geometries including dipole and quadrupole configured inductors connected in parallel with low-loss SiNx dielectric parallel-plate capacitors. The design of the resonator allows a change in the symmetry of the inductor or grounding of the capacitor to create LC resonators with: 1) inductive coupling, 2) capacitive coupling, 3) both types of coupling, or 4) greatly reduced coupling. We measured all four designs at a temperature of 30 mK at different values of power. We compare the extracted data from the four resonator types and find that both capacitive and inductive coupling can be included and that when nominally turned off, the coupling is greatly reduced from only minor changes in the circuit design. We also find a variation in the measured loss tangent of less than a few percent between the designs over a large range of internal quality factors, which are created by using SiNx as a nonlinear lossy element within the capacitor. [ABSTRACT FROM AUTHOR]

We have observed anomalous switching curves (s-curves) in a dc SQUID phase qubit. The SQUID has two Al/AlOx/\rm Al Josephson junctions in a 1.5 nH loop. One junction as a phase qubit and the other acts as a detector junction. The qubit junction area is 2 \mum^2, the critical current is 0.08 \muA and the junction has an added low-loss SiNx shunting capacitor. The 1.37 \muA detector junction is isolated from the bias leads by an on-chip inductor-capacitor (LC) network with a 130 MHz cut-off. We measure the state of the system at 20 mK by sending a short current pulse to the device and monitoring whether it switches to the voltage state. The s-curves for the ground state (0) and excited state (1) look much as expected. However, unlike previous results on phase qubits, when the device is pumped to a superposition state, the resulting s-curve is not a weighted sum of the s-curves for the 0 and 1 state. Instead, the s-curve appears to shift to lower pulse current with increasing amplitude to be in the 1 state. We examine this behavior and discuss implications for measurement of quantum superposition states in this system. [ABSTRACT FROM AUTHOR]

Inductor-Capacitor (LC) filter circuits form an essential component for the readout chain of TES detectors, in the case of frequency division multiplexing. They serve the functions of blocking wide band noise from adjacent pixels and separation of bias frequencies. A key requirement is a high quality factor Q (narrow band resonance) to guarantee voltage bias of the TES detectors, implying a full superconducting circuit, low dielectric loss capacitors and low magnetic loss inductors. Typically, Q should be larger than 500\astf [\ MHz]\astL [\muH]. Here f is the bias frequency and L the inductor value, which is coupled to the detector speed for stable electro thermal feedback response. In our case, Q must be in the range of 1000 to 10000. [ABSTRACT FROM AUTHOR]

Graphene is a relatively new material (2004) made of atomic layers of carbon arranged in a honeycomb lattice. Josephson junction devices are made from graphene by depositing two parallel superconducting leads on a graphene flake. These devices have hysteretic current-voltage characteristics with a supercurrent branch and Shapiro steps appear when irradiated with microwaves. These properties motivate us to investigate the presence of quantum metastable states similar to those found in conventional current-biased Josephson junctions. We present work investigating the nature of these metastable states for ballistic graphene Josephson junctions. We model the effective Washboard potential for these devices and estimate parameters, such as energy level spacing and critical currents, to deduce the design needed to observe metastable states. We propose devices consisting of a parallel on-chip capacitor and suspended graphene. The capacitor is needed to lower the energy level spacing down to the experimentally accessible range of 1–20 GHz. The suspended graphene helps reduce the noise that may otherwise come from two-level states in the insulating oxide layer. Moreover, back-gate voltage control of its critical current introduces another knob for quantum control. We will also report on current experimental progress in the area of fabrication of this proposed device. [ABSTRACT FROM AUTHOR]

A small high-temperature superconducting maglev propeller system model has been designed and constructed. It mainly consists of a permanent-magnet track, a superconducting maglev vehicle, two linear motors, an automatic controlling electric circuit, and a spring. The linear motors can be powered by a single- or three-phase power supply. It can be used to do many experiments in different fields of science and technology for polytechnic instruction. Some experiments such as the effect of capacitive load in the electrocircuit, the voltage of the power supply, and the initial moving speed of the maglev model on the total mechanical work of the vehicle, which is done by the linear motors in single-phase power supply, have been carried out. Results will be discussed in detail. [ABSTRACT FROM PUBLISHER]