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The paper presents a numerical study on electrodynamic behavior of the inter-pancake twin-box joints of the Poloidal Field (PF) coils of the ITER Magnet System. This work was carried out with the THELMA code, developed at the University of Bologna. The THELMA model was adapted to describe both the superconducting wires and the resistive saddle of the joint in a set of reference configurations representative of a set of experimental tests performed on a joint sample at the SULTAN facility in Villigen, Switzerland. The model was applied to analyze both the DC joint resistance measurements and the AC loss vs frequency curve, in order to obtain a full representation of the joint electromagnetic behavior. The paper reports a comparison between the numerical and experimental results and parametric studies on the impact of the main model parameters on the loss vs frequency curve. [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) will be manufactured by assembling a stack of six modules, which are under fabrication by the US ITER organization and its subcontractors. The tests of the first CS Module have been performed at the premises of the General Atomics (GA) facility in Poway (US), in order to check compliance to the ITER requirements. Among other tests, the magnet was submitted to exponential dumps of the transport current from different initial values (10, 15, 20, 22.5, 25, 35, 40 kA) down to 0 kA. These tests are aimed at conducting DC breaker commissioning of the test facility and were used to measure the AC losses in the coil during electrodynamic transients. This paper presents the results of these measurements, along with a comparison with analytical computations of the losses in the magnet. [ABSTRACT FROM AUTHOR]

This paper analyses the current distribution in no-insulation (NI) coils in a layer-wound configuration. The investigation aims at comparing the electrical characteristic of two coils wound from the same BSCCO tape, with or without electrical insulation between turns. Both coils are characterized by a very similar geometry, with the same number of turns and layers. Both coils, cooled in liquid nitrogen bath, are charged until the tape critical current is exceeded. To interpret the measurements and analyze the current distribution within the winding, a lumped-parameter equivalent electrical circuit is developed and solved numerically in a time-varying regime. The model results are compared with the signals acquired through voltage taps soldered at the same locations in both coils. Finally, the model is applied to investigate the impact of the transverse contact resistance and to estimate the most stressed locations of the coil during charging, in terms of power produced by Joule effect. [ABSTRACT FROM AUTHOR]

The volume integral equation method based on the current vector potential approximated by means edge element basis function is a well-established approach for 3-D eddy currents computation. The application of the method is straightforward when simply connected geometries and no connection with external circuits are involved. In this case, in fact, the solving system is easily obtained based on tree–cotree decomposition of the primal graph. However, when multiply connected geometries or external generators are considered, “additional” degrees of freedom, not related to interior cotree edges of the primal graph, need to be identified and involved to assure the consistency of the numerical solution. In this article, the link between the volume integral equation method and the circuit is investigated in detail, and the circuit view is used as a guide for systematically finding the additional degrees of freedom arising in case of multiply connected geometries and/or external circuits. In particular, the dual graph is introduced as the support of the circuit and it is shown that this is the natural frame for taking the topology into account. For multiply connected geometries, the additional degrees of freedom are related to loop currents crossing one only time (or an odd number of times) any cutting surface making the domain simply connected, and are found by applying a minimum path algorithm on the dual graph forming the circuit. In case of conducting domain connected to an external generator, an extended dual graph is introduced for finding the further additional degrees of freedom. This article also researches into the possibility to replace the usual current density of the elements, obtained via facet-element shape functions and exactly matching the current of the faces, with a uniform current density obtained by means of a minimum error procedure and approximately matching the current of the faces. The use of this uniform current density, besides improving the calculation time and the accuracy of the coupling coefficients, also allows the extension of the volume integral equation method to discretizations of the problem domain made of arbitrarily shaped polyhedral elements. [ABSTRACT FROM AUTHOR]

A three-year research project, called DRYSMES 4GRID, was recently funded by the Italian Minister of Economic Development, Italy. The project, which involves five Italian partners (companies, universities, and research institutes), is aimed to demonstrate the feasibility of cost-competitive SMES based on magnesium diboride (MgB2 ) with a cryogen-free cooling bymeans of the manufacturing and the testing of a demonstrator with an objective rating of 500 kJ/200 kW. This rating is deemed suitable for disclosing the critical technological aspects of all components in view of practical applications. A further goal of the project is the assessment of the technical and economic benefits that the SMES can bring to real-world electric grids. The general outline and technical objectives of the project are presented in this paper. Preliminary design assumptions and results concerning the MgB2 coil and the power condition system are also discussed. [ABSTRACT FROM AUTHOR]

The National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL, USA, has developed a 32-T all-superconducting user magnet system combining two series-connected high-field high-temperature superconductor (HTS) nested inner coils (insert) wound with SuperPower REBCO tapes and a low-temperature superconducting (LTS) outer magnet (outsert) composed of five coils (broken in 17 electrical sections). As a part of the magnet development work, a number of quench tests were done on the HTS insert dual-coil prototype in the actual LTS outsert, mimicking the actual magnet configuration and operation. The tests on the coupled insert/outsert system were performed at 4.2 K, using a set of tailor-made quench protection heaters to be employed in the actual insert. In these tests, in the transition to the normal state, a noticeable part of the outsert stored energy could be transferred to the insert through the inductive coupling. The experimental results are analyzed here by means of a quasi-3-D COMSOL FEM model. The model, developed at the University of Bologna in collaboration with the NHMFL, enables one to calculate the coil temperature distributions, the internal voltages, and current evolution through the increase of normal zone resistances over the insert coils. A lumped parameter equivalent model of the magnet electric circuit permits including appropriately the effect of mutual inductive coupling between the insert and the outsert coils on the currents in them. Also, the model accounts for a time-varying 2-D distribution of the magnet field generated by both the insert and outsert within their coils in the event of a quench. The REBCO insert coils are described in terms of an anisotropic homogenized medium, albeit with due regard for the essentially nonlinear characteristics of the superconducting tapes and for the interturn stainless steel reinforcement and sol-gel alumina insulation. A detailed comparison between the numerical and experimental results provides detailed insights into the modes of propagation of the normal zones. [ABSTRACT FROM PUBLISHER]

The development of high temperature superconducting (HTS) DC power cables requires a detailed information on the impact of the main characteristics of the cable architecture on the electrical parameters of the superconducting tapes. This paper presents the experimental dependence of the critical current and n-value of BSCCO-2223 and (Re)BCO commercial tapes on the cabling twist pitch. DC characterizations were conducted on single tapes twisted around an insulated multistranded Cu former from an actual HTS power cable having a typical diameter of 3 cm. For these characterizations, the twist pitch was varied from 5 to 25 cm. To check that permanent degradation occurred, the critical current Ic and the n-value were measured on a flat sample holder prior to conduct the twist pitch measurements on the former. The results can be used to determine the available range of wire twist pitches to help designing HTS DC power cables. [ABSTRACT FROM PUBLISHER]

MgB2 material operating at moderate field can conveniently be considered for short-term cost-effective implementation of superconducting magnetic energy storage (SMES). Due to the intrinsic performance of this material, moderate field operation and cryogen free cooling in the range 10–20 K need to be considered. For investigating the feasibility of MgB2 based SMES technology a 10 kW—2 s system is under development. A small MgB2 coil was developed and tested as the first step of this study. The cooling was obtained by means of a cryogen-free test facility based on a two-stages Gifford–McMahon regenerative heat exchanger. A power conditioning system (PCS) was also developed in order to connect the coil with the power grid. The PCS is based on power mosfet components and consists of two parallel dc/dc boost converters and an inverter connected to a common dc bus at 100 V. Continuous operation of the coil at a charge/discharge rate up to 24 kW can be achieved by means of the PCS. Details of the layout of the coil and the thermal connection with the cryocooler are discussed in this paper. Results of cooling test are reported. Possible SMES operation is also discussed. [ABSTRACT FROM PUBLISHER]

The ability of second-generation YBCO coated conductor (CC) tapes to transport high current densities at high temperature, i.e., up to 77 K, and at very high magnetic fields, i.e., above 20 T, are pushing the use of these tapes in various applications, from magnet to power system technologies. An accurate study of their quench behavior is mandatory for the design and safe use of cables and magnets manufactured with this ceramic superconducting material. A new 2-D finite-element method (FEM) numerical quench model, which is called anisotropic model of YBCO CCs, was built for this purpose in the COMSOL Multiphysics environment. One of the most difficult issues in the modeling of the YBCO tapes with the FEM is their high aspect ratio due to the very small thickness of the YBCO layer, about 1 μm. In the model developed, the problem of the high aspect ratio of the tape is tackled by multiplying the tape thickness by a constant factor and then compensating the heat and electrical balance equations through the introduction of material anisotropic properties. The FEM model is validated by comparison with literature experimental data on minimum quench energy and normal zone propagation velocity. [ABSTRACT FROM PUBLISHER]

In this paper, a conveyor device aimed at moving objects placed on a translating chain is studied. Losses, friction, and noise reduction are the main objectives, which are obtained by magnetically levitating the chain with the aid of a system of permanent magnets placed on the chain and on the beam. A stable vertical levitation was obtained, while the horizontal instability was managed reducing the allowed gap between the chain and the beam. A customized three-phase drive unit was also realized in order to reduce the size and the inertia of the conveyor. A prototype was built and tested in order to verify the outcomes of the design. [ABSTRACT FROM AUTHOR]

The main parameter measured in the tests of the TF conductors for the ITER machine is the current sharing temperature (Tcs). In the voltmetric assessment of Tcs, the voltages are measured on the conductor jacket, due to the technical difficulties to introduce voltage taps inside the stainless steel conduit. The average voltages measured on the jacket do not exactly correspond to those that arise along the single strands, as shown by the presence of early voltages arising during the current ramp up, when the cable is still in the superconducting phase. It is therefore not trivial to evaluate the difference between the cable and jacket voltages, that gives rise to an experimental error in the measurement of Tcs. This paper reports the results of a vast simulation campaign performed with a detailed electromagnetic model of the Cable in Conduit Conductor, in which the origin and the extent of these differences have been investigated, giving an estimate for the experimental error. The impact on measurements of other sources of error such as the signal/noise ratio and the error in the temperature measurements is also reported. [ABSTRACT FROM PUBLISHER]

Liquid storage of gaseous fuel on board of vehicles as possible alternative to high-pressure storage is receiving an increasing attention because of the higher mileage, the lower cost of the tank, and the faster refill allowable. The research effort devoted to liquid storage is also boosting the advance of cryogenics on board of vehicles, thus opening the way to the synergic use of superconductors. In such a context, superconducting magnetic energy storage (SMES) for regenerative braking may represent a possible alternative to electrochemical batteries or to developing technologies such as supercapacitors or flywheels. In this paper, the feasibility of SMES for regenerative braking on board of hybrid vehicles with cryogenic fuel tank is investigated. Possible application scenarios are discussed. The design of the superconducting magnet based on commercially available superconducting tapes and the cooling are addressed. The performance of the power control system is also investigated by means of a MATLAB/Simulink simulation model. [ABSTRACT FROM AUTHOR]

A magnetization-based formulation of the volume integral equations method for 3-D magnetostatics is discussed. The magnetization of each element is related, via the constitutive law of the material, to the average magnetic flux density within the element rather than to the value at the center as is usually done. This assumption leads to more accurate distribution of magnetization and allows a faster convergence of the solution. Moreover, it leads to more symmetric matrix of the coefficients and reduces the numerical instability due to looping patterns of magnetization, which is inherent to integral methods. The formulation is made effective by the use of a hybrid numerical and analytical approach, which allows for the fast and accurate calculation of the coefficients. The proposed model is validated and compared with the usual model both for saturable and linear material with high susceptibility. [ABSTRACT FROM PUBLISHER]

The measurement of the current sharing temperature of a Cable in Conduit Conductor is a complex task. The voltage traces measured on the conduit (jacket) of these conductors during tests, give V∙I characteristics that significantly differ from the typical transition from the superconducting to the resistive state measured on single strands. In these measurements, after an initial ramping of the transport current up to the test value, the temperature is increased by steps until the resistive transition occurs. However, even in the first phase of the current ramping, when the cable is still fully or almost superconductive, early voltages are measured along the jacket at different angular positions around the cable. In particular, this was observed in the ITER TF conductors recently tested in the SULTAN facility at Villigen PSI, Switzerland. These samples showed significant ramps of voltages taken in the proximity of the joints and terminations. The present paper gives a possible qualitative and quantitative explanation for this mechanism. Numerical simulations are also shown which reproduce the scattering of the voltages measured around the jacket at a given location, showing the effect of the voltage taps position along the jacket in a six sub-cable model. [ABSTRACT FROM AUTHOR]

A novel energy storage system based on a SMES cooled by cryogenic fuel is being developed at the Dept. of Electrical Engineering of the University of Bologna. The system represents an alternative solution with respect to nowadays battery packs for the storage of electrical energy with large specific power. The device may find suitable application on board of road vehicles fed by liquid hydrogen with hybrid power-train (internal combustion engine and electric motor/generation), where a cryogenic tank is already present and no additional cryogenic costs are needed. The housing of the SMES inside the tank used for fuel storage, allows the exploitation of the thermal power required for the continuous evaporation of fuel for feeding the engine to remove the AC losses from the magnet, thus avoiding the need of externally supplied cooling power. In this paper both the design of the magnet and its operation in combination with electronic converter and electric motor/generator during charge/discharge cycles are discussed. Moreover the ongoing activity for the development of a laboratory-scale prototype using MgB2 superconductor is presented. [ABSTRACT FROM AUTHOR]

The THELMA code is used to study the coupled thermal-hydraulic electro-magnetic problem of the current and temperature distribution inside the TFPRO2 Nb3 Sn SULTAN sample, which was tested in 2007. The code computes self-consistent voltage and temperature values both on the jacket, where they are measured, and inside the cable, where they are more directly representative of the conductor performance. The measured temperature gradients, related to non-uniform Joule heating at the joint and in the high-field region, as well as to non uniform current distribution, are reasonably well reproduced by the model, together with the voltage-current characteristics. [ABSTRACT FROM AUTHOR]

The paper presents the results of a numerical analysis campaign which studies the steady-state behavior and the typical tests (current-sharing temperature and critical current measurements) foreseen for the SULTAN samples of the ITER TF reference conductor, with special emphasis to the current and electric field distribution among and along the sub-cables. In this analysis, the sample geometrical parameters (twist pitch, joint/termination length) and some electrical parameters (joint, termination and inter-bundle resistance) are supposed to range in their design or their measured boundaries, in order to understand their individual effect on the conductor performances and the test conditions. [ABSTRACT FROM AUTHOR]

We have analyzed the characteristics of dc-induction heating of aluminium billets both numerically and experimentally and developed a numerical model for the calculation of the power and temperature distributions inside the billet during the heating. We validated the model by comparison with the experimental results from a laboratory-scale prototype using permanent magnets. We studied the heating process of a real scale system by means of the model, taking into account the weakening of the mechanical properties during the heating. We provide an example of design of an industrial scale dc induction heater. [ABSTRACT FROM AUTHOR]

The stability of Nb3Sn superconducting wires is a crucial issue in the design and operation of reliable superconducting magnets. High current density magnets, such as those presently developed for future accelerator projects, may be subject to premature quenches due to local releases of energy. In this paper we study the results of stability experiments that have been performed using a single mode Diode Laser with an optical fiber to illuminate the superconducting strand surface and trigger fast quenches. The development and propagation of laser-induced quenches have been measured on Nb3Sn strands in LHe bath by means of three voltage taps. This paper deals with the numerical analysis of the experimental results. A coupled electric and thermal model has been developed to study the quench propagation. The experimental evidence of a different qualitative behavior of the voltage traces recorded on Nb3Sn strands with respect to NbTi strands is explained by means of a more detailed physical model of Nb3Sn strands, that takes into account electrical and thermal transverse resistances. [ABSTRACT FROM AUTHOR]

Most magnets designed for thermonuclear fusion experiments rely on the cable-in-conduit conductor technology. These cables are made of several hundreds or thousands of multi- filamentary superconducting strands. The strands are refrigerated by a flow of liquid helium in forced convection through a conduit, usually made of aluminum or stainless steel. The complexity of the manufacturing techniques makes it very difficult to perform direct voltage measurements inside the jacket of these cables. Voltage taps are usually placed on the jacket outer surface, deriving relevant information about the inner cable electrical characteristics. In the present study, an electromagnetic model is presented that allows us to take into account the presence of the jacket and its interactions with the superconducting cable. Some unexpected qualitative behaviors of the voltage signals detected on the jacket, whose interpretation is currently under debate in the scientific community, are reproduced by the model. [ABSTRACT FROM AUTHOR]

Recent progress in material processing has enabled the fabrication of large single grain YBCO hulks having the potential to trap a magnetic field much stronger than that of conventional permanent magnets, thus opening the way to new applications in the field of power electric machinery. However, for YBCO bulks to find a broad use, a suitable magnetization process must be developed. In fact, the value of the trapped field as well as the stability with respect to the time and the shape of the profile strongly depend on the parameters of the magnetization process, i.e. the peak value and the waveform of the applied field and the operating temperature of the bulk. In this paper such a dependence is numerically investigated. [ABSTRACT FROM AUTHOR]

The evaluation of electrical coupling parameters in multistrand cables is a fundamental prerequisite for the calculation of current distribution and ac-losses in superconducting cables. The theoretical evaluation of these parameters requires a detailed description of the cable geometry. A code for the geometric description of generic multistrand multistage cables and for the calculation of the strand self- and mutual inductance coefficients has been developed. An extensive measurement campaign using straight and wound twisted multistage copper cables has been performed in order to validate the numerical model. An indirect measurement method has been used for the evaluation of the self-inductances of the wires in the straight cable. These results build a database that can be used to validate several numerical codes written in recent years for the analysis of electrical coupling parameters in superconducting cables. [ABSTRACT FROM AUTHOR]

In order to investigate the reciprocal interaction between a SFCL and the Power System an equivalent circuit of the device needs to be introduced in a power system simulator. In this paper the equivalent circuit of a magnetic shield type SFCL, consisting of two coupled electric and thermal networks, is obtained starting from the integral formulation of the coupled electromagnetic-thermal problem inside the device. The numeric waveforms of current and voltage across an SFCL during a fault are calculated and compared with the experimental ones. [ABSTRACT FROM AUTHOR]

The modeling of current distribution and ac losses in multistrand superconducting cables is strictly related to the evaluation of the cable electric parameters. A perfect knowledge of these parameters is however impossible due to the complicated manufacturing process. Strand deviations from the nominal geometry and interstrand conductance changes occur in the cable compaction process. Statistical approaches can however be applied to deal with these issues. This paper reports a sensitivity analysis aimed to determine the effects of strand deviations from the nominal geometry. The deviations, however, are not directly imposed on the mutual inductances matrix, as this approach can lead to misleading results if the final matrices do not correspond to physically possible configurations. The statistical deviations are imposed on the strands geometry, keeping the strands in physically possible locations by means of geometric constraints. A code for the electromagnetic analysis of superconducting cables is then applied to the calculation of current distribution and ac losses in the different configurations, evaluating the relevance of the main parameters variation. [ABSTRACT FROM AUTHOR]

In order to investigate how a superconducting fault current limiter (SFCL) can enhance the performance of a power system, an accurate circuit model of the device needs to be introduced in power system simulators. In this paper, we present a ifnite-element numerical model to calculate the time evolution of the voltage across a magnetic-shield-type SF CL, when it is connected to an external circuit. The calculation of the voltage is carried out by using the energy conservation law, and requires the calculation, at any instant, of the current density distribution inside the super- conducting tube and magnetization distribution inside the ferromagnetic core of the device. These distributions are determined by means of two coupled equivalent electric and magnetic circuits, whose topology and components are obtained through the spatial integration of quasi-static form of Maxwell equations. Comparisons between numerical and experimental results are shown. [ABSTRACT FROM AUTHOR]

The electromagnetic models developed in the recent years to study current distribution and ac losses in superconducting magnets have focussed on detailed descriptions of either cables or joints/terminations, usually considered separately. A more accurate physical description of the magnet system requires to model simultaneously the different parts of cable, the joints between them and the cable terminations. In this work we present the coupling of a distributed parameters circuit model of the cable with a simple lumped parameters resistive model of the joints and terminations. The principles and results of the coupling strategy are illustrated and validated by means of a comparison with the analytical solution of the problem found for triplex cables. [ABSTRACT FROM AUTHOR]

Presents a numerical model to calculate the distribution of magnetization inside a superconducting bulk when a time-varying magnetic field is applied. Description of the mathematical model; Investigation of the dynamic electromagnetic behavior of a melt-processed ring-shaped superconducting bulk using a pulsed-field magnetization process.

Describes a regularization process designed to calculate electric and magnetic fields, potentials and energies by means of integral expressions. Solution of a scalar Poisson equation in whole space; Study on the dependence of the error on the value of the positive parameter; Calculation of an a priori upper bound on the error.

A three-year research project, called DRYSMES 4GRID, was recently funded by the Italian Minister of Economic Development, Italy. The project, which involves five Italian partners (companies, universities, and research institutes), is aimed to demonstrate the feasibility of cost-competitive SMES based on magnesium diboride (MgB2 ) with a cryogen-free cooling bymeans of the manufacturing and the testing of a demonstrator with an objective rating of 500 kJ/200 kW. This rating is deemed suitable for disclosing the critical technological aspects of all components in view of practical applications. A further goal of the project is the assessment of the technical and economic benefits that the SMES can bring to real-world electric grids. The general outline and technical objectives of the project are presented in this paper. Preliminary design assumptions and results concerning the MgB2 coil and the power condition system are also discussed. [ABSTRACT FROM AUTHOR]