Search

High-temperature superconducting (HTS) bulk YBa2Cu3O7‐x (YBCO) can achieve self-stable magnetic levitation (maglev) over a permanent magnet (PM) for its inherent flux pinning effect, which has considerable potential for engineering applications. The complicated vibration response, however, is lacking in research for the nonlinearity of the interaction force between the HTS bulks and PMs. This paper mainly focuses on the subharmonic resonance of the HTS bulks YBCO levitating above the PMs in Halbach array, which are in reciprocating motion, by numerical simulations. In general, the motion of HTS bulks is approximately harmonic under limited excitation. When the amplitude and frequency of the excitation satisfy certain conditions, the dynamical system undergoes a period-double bifurcation, and then, the subharmonic resonance occurs. Moreover, the period-double bifurcation brings the jump phenomenon when the frequency of excitation increases and decreases at the double of eigenfrequency nearby. Simulations show that a suitable damping is able to reduce the vibration markedly. The subharmonic resonance region in an amplitude-frequency plane is presented in this paper finally. In a word, the subharmonic resonance would occur in an HTS maglev system under certain conditions and its prediction is numerically studied here with a nonlinear mathematics model of the levitation force. [ABSTRACT FROM AUTHOR]

With the technological advancement of magnetic materials and semiconductor devices, the use of high-frequency magnetic link made of high-saturation induction and low specific core loss nanocrystalline alloy has been gaining popularity to replace the common dc link or ac link specially in integrating multiple renewable sources to the grid. The magnetic integration of multiple renewable sources through a common magnetic link has a number of advantages including galvanic isolation compared with the common dc or ac link. However, the magnetic response of the common magnetic link under multi-input excitations highly affects the energy conversion efficiency. To the best of the authors’ knowledge, the magnetic response of an advanced magnetic-material-based magnetic link under multi-input excitations has not been well investigated in the literature. In this paper, a systematic investigation is carried out to interconnect multiple sources through a common magnetic link. The magnetic response and the procedure used in the investigation are also presented and discussed in this paper. [ABSTRACT FROM AUTHOR]

A medium-voltage ac network is commonly used to interconnect wind turbines to the offshore substation, which can create significant power losses, as the distance between wind turbine and offshore substation can vary from 5 to 9 km. The copper-conductor-based high-voltage dc (HVDC) or high-voltage ac (HVAC) transmission lines are generally used to transmit the electrical power from the offshore substations to the onshore grids. With the recent advancement of the high-temperature superconducting (HTS) cables, it is now possible to replace the traditional HVAC/HVDC transmission lines with a medium-voltage dc (MVDC) cables. A new MVDC converter is proposed in this paper to convert the generator low ac output voltage to MVDC directly. The proposed new technology not only eliminates the requirement of low-frequency heavy and large step-up transformers and line filters, but can also eliminate the voltage conversion stages to allow the entire power transmission networks to use MVDC HTS cables. A compact, lightweight, and efficient high-frequency common magnetic link is used in the proposed converter. The magnetic link can inherently solve the isolation problem. In this paper, a scale-down prototype converter is developed in the laboratory to validate the feasibility of the proposed MVDC converter. [ABSTRACT FROM AUTHOR]

This paper presents an electromagnetic design of a permanent magnet superconducting wind power generator with different stator teeth structures and armature winding arrangements. The main contribution of this paper is that a novel stator configuration is proposed, which is beneficial for superconducting machines. The topology of tapering poles makes it possible for the machine to carry larger current without severe magnetic saturation in the stator teeth. Meantime, the distributed arrangement of wires in the stator slot can reduce the ac loss in the same output power condition. Finite element analysis with commercial software is used to support these results. [ABSTRACT FROM AUTHOR]

With the growing use of wind power in power systems, the requirements of low-voltage ride-through (LVRT) have been proposed. Yet, all LVRT strategies commonly used in the doubly fed induction generator (DFIG) tend to change its running state, which brings a secondary impact to the transient stability of the system. This paper combines the output power of the DFIG with the equivalent mechanical power of the system, deducing the mathematical relationship between them, and theoretically analyzes the relationship between superconducting magnetic energy storage (SMES) access location and transient stability improvement. On this basis, this paper puts forward an SMES coordinated control scheme considering location information to improve the dynamic characteristics of grid-connected wind farm, achieving higher transient stability performance of the system. Finally, the simulation in MATLAB/Simulink verifies the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Experimental and advanced superconducting Tokamak (EAST) was designed by the Institute of Plasma Physics Chinese Academy of Sciences. The magnet system of EAST includes poloidal field (PF) coils, central solenoid (CS) coils, and toroidal field coils. The heat generated by the ac losses of PF and CS coils increases the burden of the cooling system, which reduces the critical current of the superconducting cable. Once the superconducting magnet quenches, it will pose a serious threat to the stability of the whole device. In this paper, the piecewise linear method and the finite-element analysis were used to analyze the ac loss of the EAST PF and CS coils under the specific operating current. The whole calculation process is described in detail. The final results meet the stability margin of the design of the EAST device. Meanwhile, the ac losses of PF and CS coils for EAST are theoretically evaluated in terms of the structure of magnet, the simplified current, and the distribution of the coil. The results of this paper not only provide data support for the next design and experiment of the EAST device, but provide some references for similar calculation of other large nuclear fusion magnets. [ABSTRACT FROM AUTHOR]

Taking into consideration the low voltage ride through (LVRT) demand proposed in grid codes, a resistive-type superconducting fault current limiter (R-SFCL) LVRT solution is presented in this paper for doubly fed induction generator (DFIG) based wind turbine generators. The installed position, equivalent modelling of R-SFCL, and technical principle for improving LVRT capability are described. Cooperative control between R-SFCL and two advanced control strategies—reactive power control (RPC) and inductance-emulating control (IEC)—are introduced in this paper to help the DFIG generate reactive power and protect key parameters during grid faults. Simulations and performance evaluation are also conducted compared with the single IEC scheme and single RPC-IEC scheme, which demonstrate the effectiveness and superiority of the proposed scheme in enhancing LVRT capability. [ABSTRACT FROM AUTHOR]

The tri-axial high-temperature superconducting (HTS) cable is the key factor to improve transmission capacity and to optimize the structure of smart grid. The HTS devices generally have large current-carrying capacity. Therefore, the electromagnetic characteristic of a composite superconducting cable with high current density becomes a key point for the application of these HTS devices. In this paper, in order to derive the electromagnetic characteristics and voltage reflection mechanism of HTS cable with fast stable convergence, the optimized equivalent estimation model for the distributed impedance and inductance parameters of HTS cable's conductor layer and shielding layer is put forward based on the optimal vector fitting algorithm with the novel partial element equivalent circuit approach, which could precisely identify the frequency-dependent stray parameters with the iteration computation of a rational function approximation via poles and residues. Accordingly, the dynamic influence behavior of the distributed parameters on the mechanism of HTS cable's electromagnetic characteristics is theoretically discussed in the paper for a complicated power system, and the feasibility and accuracy of the proposed conducted electromagnetic interference estimation method are also verified via a numerical computation and a performance experiment. [ABSTRACT FROM AUTHOR]

In this paper, the application of SMES system in the electrical multiple unit (EMU) was studied. With a new type of SMES rectifier and its novel control strategy, the EMU could immune through the over-phase region from the power off. The overvoltage impact on the related equipment due to the frequent power switch could also be reduced. With the combination of the DQ current decoupling control and transient direct control, the output power quality of the motor train grid side was obviously improved and the voltage adjustment time was significantly improved. The grid side harmonic was also suppressed, and the harmonic content was obviously reduced. All advantages on the dynamic response abilities presented above had been verified by the simulation and test results in this paper. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) soldered-stacked-square (3S) wire has been proposed as a novel potential structure for the second generation HTS wire. Twisted method is an available way to decrease the anisotropy and improve the performance of 3S wire in high field application. This paper presents a three-dimensional numerical model based on H-formulation for the 3S-twisted (3S-T) wire. AC loss is evaluated as an important parameter when 3S-T wire is applied in alternating current or magnetic field circumstances. Three different structures of 3S-T wires are considered, and the validity of the general model is verified by the corresponding experimental results. The results show that there is no significant eddy loss existing in the 3S-T wire. Moreover, if more HTS tapes are contained in 3S-T wires, the current distribution will be closer to elliptical shape and the current phase in different YBCO layers will be changed. The transport AC loss can be slightly reduced through the twisted method. The work in this paper will be helpful to understand the electromagnetic characteristics of 3S-T wire. [ABSTRACT FROM AUTHOR]

The SC200 proton therapy facility is consisting of a superconducting cyclotron, a gantry treatment room and a fixed beam room. The proton beams are transported mainly with beam transport devices, such as dipole magnets, quadrupole magnets, and corrector magnets which lie on the beam transport line layout of which is based on the beam optics design. A series of dipole, quadrupole, and corrector magnets ultimately make high-quality transmission of proton beams possible. Dipole magnets are mainly for beams deflection, quadrupole magnets are for beam focusing, and corrector magnets for orbit correction of beams. This paper shows the design of such magnets for the beam transport line. Besides, main parameters of magnets are presented and magnetic analysis work is also illustrated in this paper. The magnetic fields of dipole and quadrupole magnets are measured by hall mapping system and rotary coil measuring system. The results show that the measuring results are a little worse than the simulation results. However, both methods can meet the design requirement and the basic trend is similar to each other. [ABSTRACT FROM AUTHOR]

Nonuniform electric field distribution is one of the key issues for the superconducting cable terminals. This paper tries to modify the electric field distribution in HTS dc cable terminals by the nonlinear conductive epoxy/ZnO insulation, instead of the insulation with a fixed conductivity. The nonlinear conductivity of epoxy/ZnO composites is measured, and a finite element simulation model of the +100 kV HTS dc cable terminal is established to analyze the electric field distribution at the steady and transient state. The results show that the field-dependent conductivity has a great effect on the dc electric field distribution. If the nonlinear coefficient is excessively large, the electric field in the polypropylene laminated paper (PPLP) will be extremely strong; otherwise, the electric field in the terminal insulation will be extremely strong. The epoxy/ZnO composites with an appropriate nonlinear conductivity can effectively uniform the electric field distribution at the triple-junction and the stress cone surface. When the switching overvoltage impulse superimposed dc voltage is applied, the maximum field is always located in the cable insulation of PPLP, which is because that the electric field distribution in the stress cone is mainly dependent on the capacitance characteristics of the insulation instead of the conductivity. The nonlinear conductive epoxy/ZnO composites could play an important role in promoting the development of stress cone of HTS dc cable terminals. [ABSTRACT FROM AUTHOR]

Short-circuit faults are inevitable in split-winding transformers with stabilizing windings, and the resulting transient electromagnetic force may cause detrimental damages to the equipment. This paper focuses on a comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults. In this regard, a FEM based on a field-circuit coupled approach is proposed. Also, a SFFZ10-88000-kVA split-winding transformer with stabilizing windings is used as a prototype to investigate its transient performances with both full-crossing and half-crossing conditions under different short-circuit faults. The symmetrical component method is presented to compute short-circuit currents to compare with the simulation ones, and a prototype test model is established to verify the correctness of the proposed method. The results reveal that the axial forces exerted on the winding in half-crossing short-circuit faults are generally larger than those in full-crossing short-circuit faults. Moreover, there is a considerable short-circuit force in the stabilizing winding in cases of a single-phase earthed fault and a two-phase earthed fault and there is no current in the stabilizing winding under other short-circuit fault cases. The numerical modeling approach dealt with in this paper is expected to be useful in the design of the split-winding transformer with stabilizing windings. [ABSTRACT FROM AUTHOR]

Because of the large ambient noise in biomagnetic measurements, it is usually necessary to use a gradiometer to reduce the environmental noise [A. Hayashi, Y. Hirata, and S. Kuriki, “Coil cancellation scheme with an electronic gradiometer for the reduction of magnetic field noise,” J. Magn. Soc. Jpn., vol. 29, no. 4, pp. 477–481, 2005.]. In order to prevent noise coupling into the SQUID from the on-chip input coil, it is also necessary to cover the chip with a niobium cylinder [S. L. Zhang et al., “A novel superconducting quantum interference device for biomagnetic measurements,” Sci. Bull., vol. 58, no. 24, pp. 2917–2919, 2013.], [J. R. Claycomb and J. H. Miller, Jr., “Superconducting magnetic shields for SQUID applications,” Rev. Sci. Instrum., vol. 70, no. 12, pp. 4562–4568, 1999.]. This paper focuses on the possible impact of introducing a niobium cylinder on the output of a SQUID gradiometer and how to reduce this effect. In this paper, the effect of the niobium cylinder on the output is equivalent to imbalance in simulation and measurement. Changing the relative position of the niobium cylinder makes the equivalent imbalance of the SQUID gradiometer coil less than 1%, which is caused by manual winding. [ABSTRACT FROM AUTHOR]

Poloidal field coil no. 4 (PF4) cryostat feedthrough (CFT) is a key subcomponent of ITER feeder system. The superconducting busbars of PF4 CFT have insulation protection layer, which consists of several half-overlapped pre-preg and glass Kapton for main structure. Base on the special busbar structure, how to do the electrical tests for production final acceptance was studied. In this paper, three kinds of electrical tests for PF4 CFT busbar insulation acceptance were introduced, include direct current high-voltage test, alternating current partial discharge test, and Paschen test. On-site environment control, electrodes connection configuration, and some detail processes of these electrical tests were introduced. Some test results of leakage current were showed in this paper to guarantee the high quality of PF4 CFT superconducting busbar protection insulation. [ABSTRACT FROM AUTHOR]

Narrowing high-temperature superconducting (HTS) tapes can effectively enhance the ability of antielectromagnetic interference. In addition, different structures of HTS wires are necessary for HTS applications. Thereby, a kind of soldered-stacked-square (3S) HTS Wires has been proposed. This paper presents a process of fabricating several 3S HTS wires. A normal second-generation (2G) HTS tape having 4-mm width was narrowed into four 1-mm-width narrow HTS tapes. The main propose of this paper is to study different effects of mechanical force on the critical current of 3S HTS wires. Therefore, we measured the critical current variation of these wires from the torsion, bending, and tension effects points of view, respectively. Compared with their initial critical current values, if the reduction of the influenced critical current is smaller than 5%, it can be considered that these 3S HTS wires are workable. Based on the results of the experiment, the limitations of mechanical force for these wire applications are: minimal twisting pitch of 64 mm, minimal bending diameter of 54 mm, and maximum tensile force of 374 N. [ABSTRACT FROM AUTHOR]

In this paper, a novel active shimming method is proposed to minimize the shim coil–magnet and the shim coil–shim coil magnetic couplings simultaneously. In standard superconducting shim coil designs, each shim coil is usually designed individually to correct specific field harmonic components of the inhomogeneous field without considering the magnetic couplings among the shim coils and the main magnet. In particular, a strong interaction among the zonal shim coils and the main magnet can lead to a series of problems, like the drift of main field, instability of field homogeneity, and even destruction of coils. In this paper, magnetic decoupling techniques for reducing magnetic interactions among the zonal shim coils and the main magnet are developed. To complete a set of independent shim coils design, a nonlinear optimization model considering the field deviation and magnetic coupling is established. To improve the efficiency and solution quality of the involved optimization problem, the nonlinear model is first converted to a linear one by using the McCormick envelopes scheme. Through linear programming (LP), the optimal topology and preliminary positions of the shim coils are determined. To further optimize the position and turn numbers of the shim coil, a nonlinear programming (NLP) is then implemented to achieve desired field uniformity. In order to verify the feasibility and effectiveness of the proposed method, a simulation design of two sets of shim coils, Z2 and Z4, for a practical 9.4T magnet for whole-body magnetic resonance imaging (MRI) is presented. Compared with coils designed by conventional methods, magnetic coupling between the zonal shim coils and the main magnet had been effectively reduced. And also, magnetic coupling between the zonal shim coils had also been minimized as much as possible, which consequently improve the stability and safety of the MRI magnet system. [ABSTRACT FROM AUTHOR]

Toward the practical development of high-voltage high-temperature superconducting (HTS) cables, high electrical insulation characteristics, and low dielectric loss become important. Dielectric loss drastically increases with the increase of operation voltage of HTS cables. Therefore, it is highly expected to find a novel insulating material with low dielectric loss for the high-voltage HTS cables. We have focused on Tyvek ^\circledR, polyethylene (PE) nonwoven fabric, and Tyvek ^\circledR/PE, a syntactic paper bonding PE-sheet on Tyvek^\circledR by heat, as low dielectric loss materials. In this paper, we investigated fundamental partial discharge inception characteristics and their mechanisms of Tyvek^\circledR immersed in liquid nitrogen (LN2).In addition, we compared the electrical insulation characteristics of Tyvek^\circledR, Tyvek ^\circledR/PE, and polypropylene laminated paper (PPLP^\circledR), and discussed their mechanisms. [ABSTRACT FROM PUBLISHER]

To optimize the insulation design of high-temperature superconductivity (HTS) cable, the multilayer wrapping cable insulation properties in the liquid nitrogen should be studied. In this paper, we investigated the breakdown properties of multilayer wrapping of cable insulation in liquid nitrogen. AC and dc breakdown tests of a minimodel cable with an insulation floor composed of polypropylene laminate paper (PPLP), PPLP/100HN (DuPont polyimide film), PPLP/100CR (DuPont polyimide film), and PPLP/150FCR019 (DuPont polyimide film) and of singer-layer sheets, including PPLP, 100HN, 100CR, and 150FCR019, respectively, were performed in liquid nitrogen. The breakdown characteristics of the sheets and model cable insulation consisting of PPLP and composite insulation schemes according to the arrangement of PPLP/HN, PPLP/100CR, and PPLP/150FCR019 were compared. For the sheets, the ac breakdown strength of 100HN is greater than that of 100CR; this may be because there are large amounts of organic-inorganic interface in 100CR. The dc breakdown strength of 100CR is greater than that of 100HN, which may be because the space charge of 100CR homogenizes the electric field. For the minimodel cable insulation, the dc and ac breakdown strengths of the composite insulation in which the third layer of wrapping tape insulation material was composed of three layers of 100HN, which is overlapped completely, are greater than those of the insulation consisting of PPLP and other composite insulations. [ABSTRACT FROM PUBLISHER]

Future high-field accelerator magnets, like the ones foreseen in the design study of the FCC project and for the EuCARD2 “Future Magnets” program, operate with magnetic fields in the range of 16–20 T. For such magnets the energy density is higher than in the accelerator magnets at present in operation, posing a challenge for the quench protection. Traditionally, quench protection has relied on generating large normal zones in the coil by firing quench protection heaters. The increase of the coil internal resistance results in a fast current decay. This paper introduces the Inductively Coupled Energy Dissipater (ICED) system, based on low resistance loops, which are inductively coupled with the coil. These loops greatly accelerate the current decay by rapidly extracting the energy from the coil, thereby lowering its peak temperature. Because of the potential reduction in stabilizer volume within the conductor, ICED may enable higher engineering current densities in the coil than with the protection relying entirely on dissipating the magnet's energy in the windings. The efficiency of ICED as a passive quench protection system is studied in this paper. We present the effect of such protection structure, on the field quality during standard powering of the magnets and on the cryogenic system. We study electromagnetic forces in the loops and mechanically stable geometric locations within the magnet structure. For the proof of the concept, this system has been employed in Feather-M2 dipole demonstrator. We compare our modeling approach to results gained from a cryogenic test. [ABSTRACT FROM AUTHOR]

Superconducting QUantum Interference Devices (SQUIDs) based on nanobridge junctions have shown increasing promise for single particle detection. This paper describes the development of the fabrication of improved and reproducible nanobridge junctions fabricated by focused ion beam (FIB) milling from niobium thin films. Although the very low noise properties of nanobridge SQUIDs are well known, the nature of the milling process is little understood at the level of local superconducting properties. In this paper, we report the results for nanobridge Josephson devices and SQUIDs, which we believe are the first to be made by Xenon (Xe) FIB milling. Temperature-dependent current–voltage behavior, microwave-induced Shapiro steps, and SQUID response to magnetic fields have been measured. We make preliminary comparisons with nominally identical devices milled from Nb thin films using either Xe or Ga ions. [ABSTRACT FROM AUTHOR]

Resistive superconducting current limiter (RSFCL) is a focus in the development of current limit technology, especially in the field of ac transmission. It has a significant effect of limiting current. However, the traditional double-wound noninductive pancake coil has an inevitable drawback. Due to its special structure the flashover would occur easily during the fault in high-voltage environment. That would make the SFCL working in an uncontrolled state. So, novel coil structures or connection modes are demanded to meet the protection of voltage source converter-based high voltage direct current. In this paper, the magnetic distribution of different flux coupling connection modes of the coils is analyzed through the simulations based on continuous pancake coil. A flux coupling type SFCL with pancake coils is designed and fabricated. The limitation process of the SFCL coils is analyzed through simulations and experiments in millisecond level. The parallel current sharing characteristics of the coils are researched through experiments in different impulse current. Meanwhile, a continuous pancake coil is made to study the series voltage sharing features of the coil. The result of this paper has certain guiding significance in the design of dc RSFCL. [ABSTRACT FROM AUTHOR]

The second-generation high-temperature superconducting tapes (2G-HTS) such as the REBCO coated conductors are known for their strong mechanical properties and high current carrying capacity with low ac losses compared with first-generation HTS tapes as well as low-temperature superconductors. Therefore, they seem to be good candidates to assemble coils for superconducting rotating electric machines (SuREMs). In this article, to investigate the influence of a soft magnetic composite (SMC) material on the dc and ac HTS coil performances at cryogenic temperatures, GdBCO- and YBCO-based commercial tapes from different manufactures were used to assemble ten HTS coils in double-pancake configuration. These tapes were wound using two different core structures, i.e., fixed and movable cores, having the same circular shape but different diameters as well as materials, i.e., fiberglass and SMC. Critical currents and ac transport current losses of these coils were measured using the electrical method. To evaluate the parallel and perpendicular components of the profile of magnetic flux density for each assembled HTS coil, a finite element model has been developed using Maxwell 2D. Eventually, the performance of different coils for SuREM application was discussed. [ABSTRACT FROM AUTHOR]

Critical current density is an important parameter reflecting power transmission capacity of HTS cable. Based on the superconducting energy pipeline, a tightly wound cable structure along arc of the pipeline is studied in this paper. Critical current density of electromagnetic thermal coupling is calculated and optimized superconducting cable structure is evaluated. Experimental results are useful to the design of high-temperature superconducting (HTS) cable in energy pipelines. [ABSTRACT FROM AUTHOR]

Various strand concept for high-temperature superconductor (HTS) flat tapes have been developed in the past few years for fusion magnet applications. We developed a round HTS strand with soldered multilayer copper tapes as filler and support called SaMiT following the technic path of twisted stacked-tape cable. DC tests performed under bending and twisting condition demonstrated that the proposed design of the HTS strand is promising in the high current cable and magnet application, but the study on electromechanical properties against the transverse and cyclic load is still needed. A press device was designed to measure the critical current of SaMiT sample at 77 K and self-field as a function of transverse and cyclic load to simulate the electromagnetic force load during the magnet operation. Transverse load amplitudes have been applied up to 40 MPa and cyclic load up to 1000 cycles at certain load amplitude. The experimental results are presented and structural optimization suggestions are discussed with visual inspection and analysis. [ABSTRACT FROM AUTHOR]

The local thermal disturbance will produce a joule heat. When the joule heat is larger than the minimum quench energy (MQE), it will lead to the phenomenon of a quench. The same problem exists in stacked superconducting tapes. In this article, the defects in REBCO tapes were created using the bending method. The voltage and temperature traces were measured during the quench process. The quench characteristics of the MQE and normal zone propagation velocity (NZPV) of the stacked REBCO tapes were investigated of different stacked REBCO tapes in the following configurations: two defects-free tapes; one defect-free tape and one tape with a defect; and both tapes with defects. The MQE of the stacked tapes with the defect is smaller than that of the tapes without defects, while the NZPV of the stacked tapes with the defect is larger than that of the tapes without defects. [ABSTRACT FROM AUTHOR]

This article intends to explore the optimal electrical characteristics of different winding processes for future high-field accelerator magnet insert. In the study, five double-pancake (DPC) racetrack ReBCO coils were wound by dry winding with no insulation (NI) process, dry winding with Kapton insulation (KI) process, wet winding with KI process, wet winding with NI process, and dry winding cowound with stainless steel tape process, respectively. The five DPC racetrack coils were fabricated and tested at 77 K in the Institute of High Energy Physics, Chinese Academy of Sciences. The article mainly presented the two winding processes, dry winding with NI and cowind with 304 stainless steel tape insulation since their special self-protect character during quench and delay effects during excitation and demagnetization. Through the experiments, we studied the characteristics of different winding processes and quench protection methods, which are important for the future application of High-temperature superconducting (HTS) insert coils. [ABSTRACT FROM AUTHOR]

Trapped-flux magnets made of stacks of superconducting tapes are an interesting and important alternative to the application of rare-earth permanent magnets and trapping flux in bulk superconductors. Many applications, such as electric motors, can require the complex shapes of magnetic elements to combat issues such as demagnetization during the operation. Therefore, a reliable production technique of high temperature superconductor (HTS) stacks with different geometries is required to meet the needs of industry. In this article, a method of shaping the epoxy-glued stacks of superconducting tapes is proposed and investigated. The application of hot press allows to easily change the shape of the stack. The influence of shaping the stack on the density of trapped magnetic flux as well as critical current are presented. Experimental and numerical analyses are performed and their results are matched to find the change in the superconducting properties of the tapes. They show that with the proper process parameters the stacks can be shaped with only minor decrease of performance. However, strong degradation is observed if the applied force is too high. The observed problems are discussed and the possible solutions are proposed. [ABSTRACT FROM AUTHOR]

In this paper, we propose to study and design a coil used to magnetize, by means of a pulsed fieldmagnetization (PFM) process, an inductor of a radial flux superconducting machine with one pair of poles. Each pole contains four similar high-temperature superconducting (HTS) bulks of 30 mm diameter arranged in a square pattern. The cryostat already exists for this application and the temperature of the HTS bulks can vary from 4.2 K to their critical temperature, in a transient state. For a given primary source of energy, here a capacitor bank of 10 kJ (5mF, 2 kV) is available, the PFM process depends strongly on the value of the coil inductance used to generate pulsed field, because it defines the waveform of the current: peak value and time constant. Thus, three-dimensional modeling of the coil is required in order to be sure that its inductance and the magnetic field produced will provide a full magnetization of HTS bulks. From the practical point of view, we would like to achieve an average magnetization of each pole around 3 T. In this paper, numericalmodeling of coils with different number of turns coupled with circuit's equations is achieved. The maximum magnetic field obtained on the HTS bulks and estimated magnetization at the top center of each HTS bulk, are presented and discussed. [ABSTRACT FROM AUTHOR]

Presently, the high-speed electric machines with increased specific power are in the mainstream of research and are being developedworldwide. The high-temperature superconductor (HTS) machines allow improving the specific power even more significantly. The inductor generators are one of the perspective types of such machines. A new type of high-speed HTS electric machines is proposed in this paper. The proposed machine combines properties of generator with permanent magnets and inductor generator. In the rotor of this machine, permanent magnets are replaced by the stacks of HTS plates. In this case the HTS generator can be operated as an inductor iron-free HTS generator with combined excitation. This paper is devoted to the experiments and simulation of the proposed HTS generator. The experiment and simulation results prove the implementation of such design at three regimes: inductor, trapped-field, and combined excitation. The future development of the proposed HTS generators and perspectives of their application is discussed. [ABSTRACT FROM AUTHOR]

In previous papers, a new method to characterize HTS pellets has been presented. This method is based on the measurement of their complete penetration magnetic flux density BP . It allows determining the critical current density JC and the nvalue of the classical power law model. In this paper, a method of determination of BP of a unique HTS pellet from the measurements of the magnetic field at its top-center surface is presented. This is a simpler and cheaper method than previous methods. It uses analytical calculation based on the Biot and Savard law and numerical calculation based on power law. The maximum magnetic flux density produced by the SC pellet BZSCM is deduced from the measurement. BP is deduced from BZSCM multiplying it by a coefficient analytically calculated. The influence of JC(B) on this method is presented and analyzed. [ABSTRACT FROM AUTHOR]

We investigate the orientation of the magnetic field preserved in a stain containing iron compounds, such as ink pigment or blood, using a superconducting quantum interference device (SQUID) magnetometer system. The magnetization of a cloth or paper sample is observed by applying a vector-type SQUID gradiometer, which detects three orthogonal components of the magnetic field, andmechanical modulation, which converts dcmagnetic signals to time-varying signals detectable by SQUIDs. Numerical experiments indicate that the orientation of the magnetization could be identified by the vector-type SQUID magnetometer when the sample was moved linearly under the probe. This paper describes in detail the instrumentation of the measurement system and a proof-of-principle experiment to confirm the system's effectiveness. The obtained results suggest that the magnetization of iron-compound-containing stains preserved the orientation of the magnetic field in which they were produced, as we hypothesized. [ABSTRACT FROM AUTHOR]

This paper proposes an optimal control algorithm through lateral displacement and yaw angle in curved road of shallow-depth subway systems. In the case of the surface transportation, which has recently been introduced, curved driving performance is required for the downtown. The existing research works are the main research theme of the lateral displacement restoration control, but there is a limit to smooth operation when the curve is run only by receiving the lateral information. However, when the yaw angle displacement information is obtained, it is possible to consider the turning angle of the vehicle while the vehicle is driving in a curved road. However, it is difficult to control because the change of yaw angle is more sensitive than lateral drift. Therefore, this paper suggests an algorithm that uses yaw angle displacement control. The validity and usefulness of the proposed control algorithm is verified by experimental results using a small-scale bogie system. [ABSTRACT FROM AUTHOR]

The luminosity upgrade of the Large HadronCollider (LHC) at CERN requires the installation of additional collimators in the dispersion suppressor regions of the accelerator. The upgrade foresees the installation of one additional collimator on either side of interaction point 7 (IP7) at the location of the existing main dipoles (MBs) that will be replaced by shorter and more powerful dipoles, and of one additional collimator on either side of IP2 at the location of existing empty cryostats. This paper describes the design and the construction status of the full-length prototype of the 11-T dipole magnet, which is needed for IP7. This magnet features a two-in-one structure, like the LHC MB, impregnated coils made of Nb3Sn conductor, an inner bore of 60 mm, and a magnetic length of about 5.3 m. Two 11-T magnets are needed to replace a 15-m long MB. A by-pass cryostat placed in between the two magnets allows creating a room temperature space for the additional collimators. The magnet is designed to provide the same integrated field as the MB at nominal field. However, due to the difference in transfer function at lower field, a correction bymeans of a trim current has been considered. A full-length prototype is currently under construction at CERN with the goal of developing the manufacturing and inspection procedures prior to launch the series production. For this, new tooling has been developed and optimized during the fabrication of fully representative practice coils. This paper describes the design of the magnet, the main manufacturing steps, and corresponding quality indicators, which will be used to monitor the series production. Finally, the production and installation schedule will be presented. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results of a small-model study, from which we plan to develop and apply a full-scale field-shaking system to reduce the screening-currentinduced field (SCF) in the 800-MHz high-temperature superconducting (HTS) Insert (H800) of theMIT 1.3-GHz low-temperature superconducting (LTS)/HTS nuclear magnetic resonance magnet (1.3 G) currently under construction-the H800 is composed of three nested coils, each a stack of no-insulation (NI) REBCO double pancakes (DP). In 1.3 G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we used two NI REBCO DPs, one from Coil 2 (HCoil2) and one fromCoil 3 (HCoil3) of the three H800 coils, and placed them in the bore of a 5-T/300-mm room-temperature bore LTS background magnet. The background magnet is used not only to induce the SCF in the DPs, but also to reduce it by the fieldshaking technique. For each run, we induced the SCF in the DPs at an axial location where the external radial field BR > 0, and then, for the field shaking, moved them to another location where the external axial field Bz ⪢ BR. Due to the geometry of H800 and L500, top DPs of three H800 coils will experience the considerable radial magnetic field perpendicular to the REBCO tape surface. To examine the effect of the field shaking on the SCF, we tested each NI REBCO DP in the absence or presence of a radial field. In this paper, we report 77-K experimental results and analysis of the effect and a few significant remarks of the field shaking. [ABSTRACT FROM AUTHOR]

The 100 T pulsed magnetic field project is under development at the Wuhan National High Magnetic Field Center, Wuhan, China. Using the NI CompactRIO hardware and Lab-VIEW software platforms, a control and data acquisition system (CADAS) for the 100 T pulsed high magnetic field facility is designed and implemented. This paper briefly introduces the design of the control system and presents the aspects of the implementation. The CADAS developed in this paper communicates with three types of power supply systems and controls their discharge coordinately, and records discharge waveforms. It has been put into test, and 67.6 T pulsed magnetic field has been generated by a test three-coil magnet. [ABSTRACT FROM AUTHOR]

This paper presents a design concept of a multipole electromagnet using a parallel iron-core structure. An electromagnet can be used in many types ofmagnetic study area, such as work on magnetic susceptibility, the Hall effect research, the magnetooptical effect, and in hysteresis measurements. In electromagnets, generally, only a single probe can be used at a time due to the single pole structure, and it is challenging to measure many samples simultaneously. In this paper, a multipole electromagnet is proposed. It has a parallel iron-core structure and a high-temperature superconducting coil, unlike the conventional electromagnet system. The electromagnet with such a structure enables multiple probes to be used simultaneously. To verify the feasibility of the structure, a small-scale multipole electromagnet was designed using commercialized finite element method software. Based on the design results, a parallel iron-core and coil assemblywas fabricated and the performance of the magnet was evaluated. [ABSTRACT FROM AUTHOR]

Magnetic field measurement is one of the key contents in the field of electromagnetic protection. In this paper, a magnetic field measurement system based on distributed magnetic sensing and a high-accuracy numerical integration method is proposed. And a magnetic field sensor with simple structure, small size, and wide measurement band is designed, which includes three magnetic field measurement coils that can realize the accurate measurement of a three-dimensional magnetic field. The output of the magnetic field measurement coil is a differential signal that needs to be reduced by the integrator. To solve the problems of traditional analog integrator and common digital integrator, this paper proposes a high-precision digital integral algorithm based on Gauss algorithm, which can effectively improve the accuracy of the integrator. Test results indicate that the error of the magnetic field measurement system is less than 5%in the range of 0.05-5T. [ABSTRACT FROM AUTHOR]

In this paper we present design, construction, and preliminary results of a proof-of-concept prototype of hightemperature superconductor (HTS) shim coils operated at 77 K and energized, for the first time among all shim coils, by a flux pump, here called digital flux injector (DFI). Although the prototype shims were wound with 2-mm wide REBCO tape, and DFI with Bi2223 and REBCO tapes, the HTS Z1 and Z2 shims to be installed in the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction and operated at 4.2 K will be wound with reinforced Bi2212 wire and DFI with Nb3Sn tape. The paper concludes with two sets of Bi2212 Z1 and Z2 shims for 1.3G. [ABSTRACT FROM AUTHOR]

Compared to the conventional flux-reversal linear permanent magnet machine (FRLPM), a novel high-temperature superconducting (HTS) FRLPM with a lower number of mover teeth and higher thrust density is proposed in this paper. In order to explain the superiority of the proposed machine, the back electromotive force of the regular FRLPM, the lower mover teeth number FRLPM(LMT-FRLPM), and theLMT-FRLPMwithHTS bulks (HTS LMT-FRLPM) are derived in this paper. The analytical results are validated by the finite-element method (FEM). Furthermore, the thrust performances of the regular FRLPM, LMT-FRLPM, and HTS LMT-FRLPM at rated load are also calculated by the FEM, which verifies the outstanding thrust performances of the proposed HTS LMT-FRLPM. [ABSTRACT FROM AUTHOR]

AEuroCirCol is a conceptual design study for a post-LHC research infrastructure based on an energy-frontier 100 TeV circular hadron collider. In the frame of the high-field accelerator magnet design work package of this study, the feasibility of a 16 T dipole in a common coil configuration is being studied. This paper shows the electromagnetic design optimization performed to achieve the required field quality while minimizing the superconductor volume and taking into account the input parameters and assumptions of the EuroCirCol study. The finite element models have been used to analyze the stress distribution and deformations under the large Lorentz forces due to the very high magnetic field. Several iterations have been necessary to obtain a feasible magnet design. The 3-D electromagnetic calculations are also included in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a high power density motor design process of a thrust vector control (TVC) system to modify the thrust vector of the gimbal engine of a space launch vehicle. For this system, the high power density motor designing requires computation of the maximum current density by considering the driving environment, operating conditions, and electromagnetic optimum design process. This paper describes the computation of the maximum allowable current density in vacuum, which is the driving environment of a TVC drive motor. In addition, a Halbach magnet array structure is applied as a high output density design method for a surface-mounted synchronous motor. The characteristics of the output and loss of this structure are compared with those of an existing design. Moreover, we highlight the advantages of applying a Halbach magnet array in terms of the demagnetization resistance. [ABSTRACT FROM AUTHOR]

Flux pumps provide a contact-free method of energizing dc currents in superconducting coils. Since a predictive quantitative theory for dynamo-type flux pumps does not exist yet, the optimization of device designs must proceed through empirical experiment. In this paper, we investigate the effect of varying the annularwidth of the iron stator yokewithin a high-temperature superconducting dynamo. Reducing the dimensions of this iron yoke reduces the mass of cold iron within the dynamo, and hence has advantages in terms of weight, cryogenic efficiency, and eddy current losses. In this paper, we have investigated the dc output from an experimental high-temperature superconductor (HTS) dynamo in which the annular width of the iron yoke Δr is varied across a factor of four. Varying this dimension affects the reluctance of the magnetic circuit formed between the rotor and stator. We have shown that the dynamo output is surprisingly insensitive to the size of the iron yoke. The maximum current output (Isc ) is independent of Δr at all flux gaps. At the closest magnet-stator flux gap, a fourfold increase in Δr results in only a ~30% increase in the open circuit voltage (Voc ) and internal resistance (Rd) of the dynamo. Our results indicate that the smallest yoke studied (Δr = 6 mm) can be utilized with a 25.4-mm Nd-Fe-B rotor magnet, without adverse impact on the electrical performance of this type of HTS dynamo. [ABSTRACT FROM AUTHOR]

novel method for obtaining superior intracranial focusing field in transcranial magnetic stimulation is proposed in this paper. In order to improve stimulation intensity and focalization, a semiellipse coil pair (SEP) of special coil configuration is designed and introduced. Projected onto a plane parallel to stimulating target, the two adjacent coils are in semiellipse shapes. From the front view, the SEP is bent along a symmetrical axis at specific angles. Finite-element method is adopted to analyze the relations between the geometric structure characteristics of SEP and the three-dimensional spatial distributions of the induced electromagnetic field produced by SEP. The SEP coil is compared to a conventional figure of eight coil by the positive peak value of intracranial induced electrical field and the focusing area at a target plane located 20 mm below the scalp. Results indicate that under similar power loss, the design of SEP makes it possible to enhance the positive peak value of induced electrical field and decrease the focusing area simultaneously. A real human head modeled as homogeneous and isotropic is occupied in this paper to verify our method. [ABSTRACT FROM AUTHOR]

We have designed and built a novel high-temperature superconducting (HTS) flux pump device to charge a secondgeneration (2G) HTS double pancake coil (DPC). This device generates dc-biased ac travelling wave on sections of 2G HTS coated conductor (superconducting stator), which pumps flux into the superconducting closed loop formed by the DPC and superconducting stator. In this paper, we discuss the importance of the dc-biased field, ac travelling wave, and the travelling direction in the flux pump process, and how to control the magnetization of an HTS coil with the above factors. We have found that a pure ac travelling wave can only transport net flux into the superconducting closed loop in the presence of dc-bias field. The magnetization direction of the DPC can be reversed by reversing the dc-bias direction of the dc background field or travelling direction of the ac travelling wave. This paper shows the versatility and flexibility of this novel flux pump device in controlling the magnetization of the HTS coils, which will work as a wireless dc power source to help persistent current mode operation of a small-scaleMRI magnet built by HTS DPCs later in this project. [ABSTRACT FROM AUTHOR]

High pulsedmagnetic field is becoming widely used in physics, biology, and materials. For better performance of scientific experiments, a power supply system for 100 T magnetic field is designed at Wuhan National High Magnetic Field Center. In the preliminary design, the 100 T magnet consists of three coils in a coaxial structure. Because of the multicoil system with strongcoupling structure, the current of the outer coil will drop when the middle coil is fired. And the current drop will cause adverse effects, which increase the burden of power supply and the stress ofmagnet. Based on the analysis of the mathematical model for power supply circuit, this paper proposes a modified design for power supply system, which is an auxiliary power supply connected in series with primary power supply of the outer coil for the compensation of the current drop. Corresponding parameters, circuit topology, and control strategy of capacitors are also discussed. The simulation results of the modified design of power supply system are presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a thin superconducting solenoid is used to provide magnetic field in the CMD-3 particle detector. The solenoid is powered by a full-wave ac-dc superconducting rectifier. The rectifier is a current step-up superconducting transformer with two thermally controlled superconducting switches connected to its secondary windings. TheCMD-3 solenoid is indirectly cooled, therefore the indirect cooling method is used for the rectifier as well instead of a conventional liquid helium bath. The rectifier charges and discharges the solenoid, and provides long-term magnetic field stabilization. The CMD-3 solenoid operational magnetic field is 1.3 T with 927 A current. The rectifier charges the solenoid to this field within 7 h. Achieved long-term stability of the field is 2 × 10-5 T. The rectifier has been demonstrating good reliability since 2010, when the magnet system of the CMD-3 had been commissioned. Design, test results, and performance of the rectifier are reported in this paper. [ABSTRACT FROM AUTHOR]

Direct current (DC) circuit breakers are a key enabling technology for fault management in multiterminal highvoltage DC (HVDC) systems. DC fault isolation is challenging due to the high rate of rise of the fault current and the lack of natural current zero-crossings found in ac systems. In this paper, we present a novel superconducting hybrid dc circuit breaker that utilizes the intrinsic characteristics of the superconductor material. The automatic quench of the superconductor coil as a result of a high fault current transfers the current from the mechanical switch to the semiconductor switch. The isolating mechanical switch is able therefore to open at low current and recover its dielectric capability rapidly. A low voltage DC circuit breaker prototype has been built using a multistrand magnesium diboride (MgB2 ) coil, a vacuum interrupter, and an insulated-gate bipolar transistor module. This prototype successfully demonstrated interruption of 500 A DC within 4.4 ms. This paper presents the design of the superconducting hybrid breaker prototype and a detailed analysis of the experimental results. This superconducting hybrid dc circuit breaker has significant potential for scaling up the high-voltage and high-current applications. [ABSTRACT FROM AUTHOR]

This paper presents the design, construction, and test results of a hybrid dipole magnet. The inner coils were of second generation (2G) high-temperature superconductor (HTS) ReBCO tape and the outer coils were of low-temperature superconductor (LTS) Nb3Sn Rutherford cable. The HTS and LTS coils were independently powered and protected using different power supplies. The HTS coils were quenched many times with no degradation in performance observed. The hybrid field reached ~8.6 T, which is believed to be a record for a hybrid dipole. The maximum field was limited by the stable operation of the leads in the LTS coil at 8000 A. The HTS coils were independently ramped to 800 A, and the LTS coils to 10 000 A. With improved leads and instrumentation, this hybrid dipole is expected to produce over 13 T when the ReBCO tape in the HTS coil is aligned nearly parallel to the field. One major purpose of this program was to perform magnetization studies in the coils made with the HTS tape. Magnetization-induced field errors are expected to be small when the field is nearly parallel to the wide face of the tape. The magnetization measurements were performed at 77 K with the two racetrack coils in two orientations, with field predominantly either parallel or perpendicular to the wide face of the HTS tape. In addition, measurements were also performed at 4 K in different background fields provided by the outer Nb3Sn coils. This paper will summarize the magnetization measurements and present the quenching experience of the HTS coils in this hybrid magnet system. [ABSTRACT FROM AUTHOR]

This paper presents the design of an ultrahigh speed permanent magnet (PM) motor/generator driven at a rated output and speed of 10 kW and 70 000 r/min, respectively, for use in an electric-turbo compounding system. When designing the veryhigh speed motor/generator, the mechanical and structural safety of the rotor and losses that occur when the motor operates at high speed should be considered for safe operation. In this paper, the optimal design of the ultrahigh speed PM motor is performed with finite element analysis and structural analysis. Especially, the electromagnetic and structural characteristics based on the sleeve material are analyzed. The optimal design for PM motor, using carbon fiber is proposed not only to reduce the eddy-current loss, which prominently occurs at very-high speed, but also to ensure its structural safety. Finally, the validity of the design method and the effectiveness of the fabricated prototype of PM motor is verified through experimental tests. [ABSTRACT FROM AUTHOR]