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A comprehensive study of the quench properties of single laminated wires having a double-layered superconducting structure is presented. In particular, we have focused on the influence of the angle and intensity of an external magnetic field perpendicular to direction of the applied current on the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) values. We conclude that strong changes on the NZPV are mainly determined by the intensity of the applied current, while the orientation and magnitude of the applied field have a less but not negligible impact on the resulting NZPV. The quench parameters are also reported for the case when the applied current is considered as a constant parameter in which case the MQE has been found to reach a maximum value when the in-field critical current is the largest. [ABSTRACT FROM AUTHOR]

Since the local quench which induces electro-thermal instability if a local energy input exceeds a certain threshold called minimum quench energy (MQE), the normal zone propagates along the superconductor. Therefore, the rate of the normal zone spreading as a quench propagation velocity (νq) is an important factor in the quench detection and protection. This paper focuses on the measurement of νq as a self-protection parameter in a short sample of a high temperature superconducting Bi-2223/AgMg tape by applying the localized heat pulses, and MQE as a superconducting stability criterion. In addition, the current dependences of MQE and νq were verified in which by increasing the transport current, the rate of decreasing of MQE and the rate of increasing of νq were measured. These experiments have been done in nitrogen vapor without applying any magnetic field.

The normal zone propagation evolution of a short sample of Bi-2223/Ag/AgMg high-temperature superconducting tape has been investigated. We considered two different cooling modes; conduction-convection and only convection. For different currents, the minimum quench energy and the normal zone propagation velocity (NZPV) were measured and compared. The results show that the NZPV changes are more dominated by cooling system than the transport current. [ABSTRACT FROM AUTHOR]

In applications, superconducting wires may carry AC or DC transport current. Thus, it is important to understand the behavior of normal zone propagation in conductors and magnets under different current conditions in order to develop an effective quench protection system. In this paper, quench behavior of Ag sheathed Sr 0.6 K 0.4 Fe 2 As 2 (Sr-122 in the family of iron-based superconductor) tapes with AC and DC transport current is reported. The measurements are performed as a function of different temperature (20 K–30 K), varying transport current and operating frequency (50 Hz–250 Hz). The focus of the research is the minimum quench energy (MQE), the normal zone propagation velocity (NZPV) and the comparison of the related results with AC and DC transport current. [ABSTRACT FROM AUTHOR]

This paper describes the analysis of ITER feeder busbar, the hotspot temperature of busbar is calculated by classical method in the case of 0%, 50%, 75% and 100% extra copper (copper strands). The quench behavior of busbar is simulated by 1-D Gandalf code, and the MQE (minimum quench energy) is estimated in classical method as initial external heat in Gandalf input file. The temperature and the normal length of conductor are analyzed in the case of 0%, 50% and 100% extra copper and no helium. By hotspot temperature, conductor temperature and normal length are contrasted in different extra copper cases, it is shown that the extra copper play an important role in quench protecting. [ABSTRACT FROM AUTHOR]

Abstract: Quench propagation characteristics of YBCO tapes and coils were studied in this paper. Quench propagation in each test was initiated by a NiCr wire heater mounted on the sample tape and coil. Quench propagation velocity was measured through voltage taps and temperature sensors across different zones of the tapes and coil. Voltage taps and temperature sensors are arranged in longitudinal and radial direction of the coil. The thermal stability margin, the longitudinal quench propagation velocity for the tape and coil, radial quench propagation velocity for coil and the minimum propagation current were measured. In this study, we investigated the relationship between heat inputs and normal zone propagation velocities and the impact of operating currents on normal zone propagation velocities. We also compared the longitudinal quench propagation velocity and the radial quench propagation velocity. Furthermore, we performed numerical simulations by using a computer program based on a one-dimensional heat flow equation model for YBCO tape. The temperature longitudinal distributions of YBCO tape were simulated. The simulation results also prove the relation between heat input and normal zone propagation velocities and agree with the experimental results. [Copyright &y& Elsevier]

Abstract: SIS300 fast-cycling superconducting quadrupole magnet is developed at IHEP. Temperature margin and minimum quench energy are main parameters of stability of superconducting magnets. These parameters are important for the design and safe operation of superconducting magnets. But additional understanding for fast-cycling superconducting magnets is needed. To calculate the temperature margin one needs coupled numerical transient simulation of electromagnetic and thermal processes in the coil because critical temperature, operating temperature and AC losses are nonuniform over turns and their magnitudes vary in time during accelerator cycles. For calculation of the minimum quench energy the combination of the network model with thermal analysis is necessary, which allows one to model quench dynamics, including the effects of a current redistribution between strands of cable and spatial inhomogeneity of cable. Results for the temperature margin and the minimum quench energy for the magnet are presented and theirs dependence on various parameters is discussed. [Copyright &y& Elsevier]

In the case of motors and generators, the benefits of using superconductors could be represented by the reduction of 50% in both losses and sizes compared to the conventional machines of the same rating. The high temperature superconducting (HTS) coils wound with HTS conductors have very low normal zone propagation velocity (NZPV) and complicated quench behaviors because the conductors have a low thermal conductivity and large specific heat. According to these reasons, in case of HTS coils and magnets, it is difficult to expect the self-protection like as low temperature superconducting (LTS) coils. In this paper, we suggest a method which inserts the Cu tape between turn-turn winding in the HTS coil instead of electrical insulation to improve the self-protection ability of HTS coils. Because the thermal and electrical contacts along the transverse direction are enhanced by inserted Cu tape instead of insulator and the whole thermal stability of HTS coils would be increased. To clarify the quench behavior of this suggested coil, we investigate the normal-zone propagation properties of the fabricated HTS pancake coils wound with 2G conductor and Cu tape under the cryocooled operation using GM cryocooler. The effects of inserted Cu tape and the improved the self-protection ability for the suggested HTS coil will be discussed. [ABSTRACT FROM PUBLISHER]

Quench tests of a GdBCO racetrack pancake coil were conducted in liquid nitrogen at 77 K. Minimum quench energy and two-dimensional normal zone propagation velocities of the coil are discussed. Longitudinal normal zone propagation velocities in the curved section were almost twice those in the straight portion due to stress effects, showing that protection of the straight portion is of greater importance than protection of the curved portion when using racetrack-type, GdBCO pancake coils in large-scale rotating machines. [ABSTRACT FROM AUTHOR]

The quench characteristics, particularly the normal-zone propagation and increase in hot-spot temperature, of REBa2Cu3Ox (REBCO) coated conductors are important issues for safe operation in the superconducting applications. Although experimental data on the quench characteristics of REBCO coated conductors have been reported only limited data is available specifically on REBCO coated conductors laminated with Cu tape of thickness no less than 0.1 mm, which are expected to be used for high-current operation in future superconducting applications. Here we reported experimental measurements of the normal-zone propagation velocity (NZPV) in REBCO coated conductors laminated with Cu tape of 0.1 mm thickness at 77, 65 and 50 K in a background magnetic field. We also compared these results with the NZPV at 77 K of REBCO coated conductors laminated with Cu stabilizer tape of thickness 0.05 and 0.3 mm. [ABSTRACT FROM AUTHOR]

The superconducting coupling solenoid magnet is one of the key equipment in the Muon Ionization Cooling Experiment (MICE). The coil has an inner radius of 750 mm, length of 281 mm and thickness of 104 mm at room temperature. The peak induction in the coil is about 7.3 T with a full current of 210 A. The mechanical disturbances which might cause the instability of the impregnated superconducting magnet involve the frictional motion between conductors and the cracking of impregnated materials. In this paper, the mechanical instability of the superconducting coupling magnet was studied. This paper presents the numerical calculation results of the minimum quench energy (MQE) of the coupling magnet, as well as the dissipated strain energy in the stress concentration region when the epoxy cracks and the frictional energy caused by “stick-slip” of the conductor based on the bending theory of beam happens. Slip planes are used in the coupling coil and the frictional energy due to “slow slip” at the interface of the slip planes was also investigated. The dissipated energy was compared with MQE, and the results show that the cracking of epoxy resin in the region of shear stress concentration is the main factor for premature quench of the coil. [ABSTRACT FROM AUTHOR]

Abstract: Stability of 19-filaments MgB2/Ti/Cu/SS wires carrying the transport currents has been examined. Properties of two identical wires annealed at 600°C/2.5h and 800°C/0.5h were compared. It was found that annealing conditions influence not only the current carrying capacity of MgB2 filaments but also affect the inter-diffusion at Ti/Cu and Cu/SS interfaces, which is worsening the electrical and thermal conductivities of composite elements. Consequently, differences in wire’s resistances and I–V quenches were measured, which are correlating well with experimentally estimated minimum quench energy and normal zone propagation velocity. [Copyright &y& Elsevier]

Abstract: Measured and simulated minimum quench energies (MQE) for short samples are doubtful when estimating disturbance tolerance of an impregnated superconducting magnet. If measurements are performed at liquid cryogen, the cooling provided by the cryogen causes MQE to be high. At a conduction-cooled system, the transverse heat conduction is neglected causing low MQE. Even though these conditions can be artificially brought closer to the ones in an impregnated magnet, it is difficult to estimate by short-sample measurement the MQE of a superconducting coil. These similar difficulties are present at simulations. On the other hand, 1D and 2D measurements and simulations can be used, e.g., to compare wires or consider effect of insulation layer thickness, but according to the results only in a rough quantitative way. In this paper, we compare MQE and normal zone propagation velocity simulations of an MgB2 wire with 1D, 2D and 3D finite element method models to focus on the different results given by the models employing different dimensions. [ABSTRACT FROM AUTHOR]

Current distribution and stability of a hybrid LTS/HTS superconductor, consisting of multifilamentary NbTi/Cu and Bi2223/Ag tapes, were numerically analyzed according to power-law models. The results showed that most of current passed through the LTS and the current increased in the HTS with temperature rise when the transport current was below the critical current of the hybrid conductor. The quench propagation velocity of the hybrid conductor was smaller but its minimum quench energy was larger than those of LTS conductors, indicating that the stability of the hybrid superconducting conductor was effectively improved and a high engineering current density was simultaneously achieved. Finally, a hybrid sample, made by soldering Bi2223/Ag tape onto NbTi/Cu conductor, was prepared and tested successfully at helium temperature. The experimental results qualitatively agreed with the simulated ones. [ABSTRACT FROM AUTHOR]

Recently, the superconducting devices using cryogenic and superconducting technologies were widespread in the field of electric power. The 2G wires with YBCO superconducting layer, metal substrate and stabilizer layer are expected to be used in future superconducting applications, because it has high properties in high temperature and high magnetic fields. In order to operate safely at high transport currents, the thermal stability of the wounding wire should be addressed in terms of detection and protection against the quench. On the other hand, the understanding of the 3-dimensional normal zone expansion during a quench is very important to design the superconducting devices such as magnets and cables. This paper presents the results of an experimental study for normal zone propagation properties in the longitudinal and transverse directions using the pancake coil wound with 2G wires which have Cu and SUS stabilizers under the cryocooler cooling. And the minimum quench energy (MQE) of the pancake coils wound with two different kinds of stabilizers as functions of operating temperature and transport current will be described. [ABSTRACT FROM AUTHOR]

Studies on Yba2Cu3Ox (YBCO) coated conductor (CC) are actively underway for the practical application of high temperature superconducting (HTS) devices such as magnets, cables and fault current limiting devices because the CC has higher critical current (Jc) characteristics under high temperature and magnetic field. However, it is hard to make a long-length of YBCO CC tape with uniform critical current density using the present processing techniques. The hot spot will emerge in a local region if the critical current is non-uniform along the HTS tape, and eventually, the hot spots may cause serious damage to the HTS tape. Therefore, it is important to examine the thermal stability characteristic of the YBCO CC tape from the quench protection point of view. In this paper, the segmental critical current of a YBCO CC sample tape is measured in liquid nitrogen, and a heater is installed at the center of the sample tape in order to examine the normal zone propagation characteristics in the longitudinal direction under the adiabatic condition with a Gifford-McMahon cryocooler. Measurements are performed as a function of heat input and transport current for the operating temperatures of 77 K, 65 K and 40 K, respectively, and the results are discussed in detail. [ABSTRACT FROM AUTHOR]

The current distribution and stability of low temperature superconductor (LTS) and high temperature superconductor (HTS) hybrid superconductor, made of NbTi wire and YBCO coated-conductor, are described. The current distribution, quench propagation velocity (QPV) and the minimum quench energy (MQE) are numerically analysed by finite element method (FEM) based on the different power-law models since the n value in LTS is much larger than that in HTS. It is shown that the transport current in LTS is larger than in HTS if both of them have the same critical currents, and the ratio of transport current in LTS to that in HTS decreases with increase of the total transport current near their critical currents. The stability of the hybrid NbTi/YBCO composite conductor is also simulated, which indicates that MQE in the hybrid conductor is much higher than in NbTi wire but smaller than in YBCO conductor. However, the quench propagation velocity is in the range of low-temperature superconductor through the high-temperature superconductor. With advantages of high engineering current density and improvement of stability, the hybrid superconductor is expected to have potential application in large scale magnet and conducting-cooled magnet particularly. [ABSTRACT FROM AUTHOR]

Abstract: The minimum propagation zone (MPZ) and the minimum local energy release required for a quench (MQE) are two very important parameters in superconductors targeted to coil applications. Usually, MQE is determined from MPZ. According to recent experiments, the closed-form expressions presented for these are not applicable to conductors with low n-values, e.g. BSCCO and MgB2, but a numerical model is required. When various conductor configurations are designed it is very time consuming to measure basic conductor stability parameters, such as MQE, for each conductor. This paper presents a numerical model to determine MPZs for conductors with finite n-values. Therefore, the model gives an efficient tool for conductor manufacturers to estimate what kind of disturbances their conductors can tolerate. According to the results, MQEs for the n-value 20 at the normalized operation currents of 0.5, 0.7 and 0.9 are about 25%, 60% and 100% higher than for the n-value 50. [Copyright &y& Elsevier]

Due to their intrinsic thermal properties that lead to very slow heat diffusion, coated conductors are very difficult to protect against thermal instabilities and quench. This is particularly critical as the device increases in size and stored energy. Many experiments showing low quench propagation speeds and surface voltage distributions have identified the problem but, as of today, no models are available to perform high fidelity simulation of the quench process in a single tape, or in a full device. YBCO tapes are very promising conductors that would allow the development of high power density power devices such as generators and motors operating at liquid nitrogen temperature. The Department of Defense through the Air Force Research Laboratory launched a new project aiming at simulating quench propagation in YBCO tapes. The first step of the project deals with the understanding of the current diffusion in the different layers forming the tape. Experimental data on normal propagation zone (NZP) velocities and fault current limiters using this material show that the quench is most likely a 3-D phenomenon involving many non trivial physical phenomena. Experimental data will help to understand the physics of the quench and develop a local electromagnetic/thermal model of YBCO tapes. This paper presents the preliminary results of this work including a discussion of the physics of current sharing between layers. We will evaluate different commercial codes and present a simplified 3-D homogenized model applicable to a racetrack coil. [ABSTRACT FROM AUTHOR]

Keystoned superconducting Rutherford cables are widely used in accelerator magnets like in the LHC at CERN. An essential requirement in the cable design is its stability against local heat releases in the magnet windings originating from for example, strand movement or beam loss. Beam loss is the highest at the coil inner radius of the magnet, where also the magnetic field peaks. Also the local compaction of the cable is maximum here and hence the helium content minimum. When performing stability measurements on several superconducting Nb-Ti cables used in LHC dipole and quadrupole magnets, we observed that the stability against point-like heat disturbances is much worse very close to the cable edges as compared to the central part of the cable. The main reason is related to the geometry of the cable causing variation of many parameters across the cable width, like inter-strand electrical resistance, inter-strand heat conductivity, cooled strand surfaces and RRR. In this paper we show results of new stability experiments and thoroughly compare the data with results obtained with the numerical network model CUD!, which is updated for stability simulations. [ABSTRACT FROM AUTHOR]

Dipole magnets for the so-called SIS-300 heavy-ion synchrotron at GSI are designed to generate 6 T with a field sweep rate of 1 T/s. H is foreseen to wind the magnets with a 36 strands Nb-Ti Rutherford cable. An important issue in the cable design is sufficiently low AC loss and stability as well. In order to keep the AC loss at low level, the contact resistance between crossing strands R~ is kept high by putting a stainless steel core in the cable. The contact resistance between adjacent strands Ra is controlled by oxidation of the Sn-Ag coating of the strands, like in the LHC. In order to investigate the effect of Ra on the stability of the cable, we prepared four samples with different Ra by varying the heat treatment and applying a soldering technique, resulting in values between 1 μΩ to 9 mΩ. The stability of each sample against transient point-like heat pulses was measured. The results of the stability experiments and a comparison with calculations using the network model CUDI are presented. It is concluded that variation of Ra has a strong influence on cable stability and that optimization of Ra is mandatory to properly design the cable for the SIS-300 magnets, or likewise for similar magnets that might be used at CERN for a possible LHC injector upgrade. [ABSTRACT FROM AUTHOR]

Abstract: Recent development of CC, usually called second generation (2G) HTS, is actively in progress. Because of its higher critical current density as well as higher n-value, 2G HTS is feasible for the applications such as superconducting fault current limiter and superconducting cable. For operating the HTS equipment stably, it needs to investigate the characteristics of normal zone propagation occurred by quench. Investigations on the fundamental characteristics can be one of the indispensable foundations for research and development of power equipments. In this paper, normal zone propagation (NZP) characteristics according to various insulation materials are researched. By heating with NiCr heater and insulating with epoxy, we applied the operating current with respect to the critical current for calculation of minimum quench energy (MQE) and measurement of NZP. [Copyright &y& Elsevier]

The construction of the superconducting magnets for the LHC machine has required the supply of ∼7350 km of superconducting cables. The delivery of cables which is completed at 97 % has made use of a large part of the world wide production capacity. Ten contracts have been placed with firms in Europe, Japan, USA. The Nb-Ti and the Nb materials have been contracted by CERN. Before tendering and placing the contracts, a R&D program has combined studies at CERN and orders of finished cables of significant lengths to industry. The report will present the main results of the R&D program, the characteristics of the LHC cables, the encountered difficulties and the obtained successes during the long duration fabrication contracts of the highly sophisticated LHC superconducting cables. [ABSTRACT FROM AUTHOR]

With the successful commercialization of Bi-2223 powder-in-tube wire, many attempts to the R & D of the high-Tc superconducting (HTS) magnets for high magnetic field applications are now being implemented actively. Although operating temperature of HTS magnet must be kept in the designed level, the magnetic energy and mechanical disturbance can make the operational temperature of HTS magnet unstable. Especially, generated heat energy of inner HTS winding is apt to accumulate, so the normal region appears in HTS winding. This paper deals with the quenching characteristic of reinforced Bi-2223 wire and two bare Bi-2223 wires in adiabatic condition. The minimum quench energy (MQE) of HTS wires was affected by the material and ratio of their matrix. In the same condition, the normal zone propagation (NZP) energy of nonreinforced HTS wire was smaller than that of reinforced HTS wire. [ABSTRACT FROM AUTHOR]

Abstract: With the successful commercialization of Bi-2223 powder-in-tube wire, various attempts in the R&D of the high-T c superconducting (HTS) magnets for high magnetic field applications are being implemented actively. Operating temperature of HTS magnet has to be maintained at the designed level but the magnetic energy and mechanical disturbance can cause unstable operational temperature of HTS magnet. Especially, the generated heat energy of inner HTS winding is apt to be accumulated, so the normal region appears in HTS winding. This paper deals with the quenching characteristics of three kinds of selected Bi-2223 wires: the high current density wire (HC-A) and the high strength wire (HS-A) made by AMSC and HTS wire (HW-I) made by Innost. The Innost wire has the highest minimum quench energy (MQE). The high current density wire has the highest normal zone propagation velocity (NZPV). [Copyright &y& Elsevier]

Abstract: Quench propagation property is an important issue in stability of high-temperature superconductor for practical application. There are many factors inducing quench, such as external disturbance, operating temperature, transport current and magnetic field. Quench propagation velocity and minimum quench energy (MQE) are two important parameters to the stability and protection issues of superconducting magnet. This paper presents some analytical results about quench propagation properties of Bi-2223/Ag superconducting multifilament tape using finite element method (FEM). The results show that the temperature transition behaviors from superconducting-state to normal-state in the process of quench propagation can be conveniently simulated through establishing a suitable thermal analysis model. The simulation results of quench temperature–time traces of different location on Bi-2223/Ag superconducting tape are basically coincident with the former experimental results. These results are significant to the application of high-temperature superconductor. [Copyright &y& Elsevier]

YBCO tape is expected to be used in future HTS applications, because it has better Jc characteristic in high temperatures and in high applied magnetic fields. It is important to consider the stability in superconducting applications. To establish the stability criterion for coated conductors, the characteristics of the transition to the normal state and normal-zone propagation in YBCO sample tapes were examined experimentally and numerically. The YBCO sample tapes were produced by IBAD/PLD method. Measurements were performed as a function of both heat input and operating current for operating temperatures of 55 K, 60 K, and 65 K in a background magnetic field of 5 T. The experimental results were compared with a simulation using a newly developed computer program based on the finite element method (FEM). In the computer program, the I - V characteristics of the YBCO sample tapes were taken into account. The computer program could simulate the normal transition and propagation phenomena and its validity was confirmed. The influence of the thickness of a Ag-stabilizer on the transient thermal behavior of YBCO tapes was examined experimentally and numerically and the results were presented here. [ABSTRACT FROM AUTHOR]

The initiation and propagation of quench events in a high temperature superconducting (HTS) pancake coil were modeled using finite element software package ANSYS. The nonlinear temperature dependent heat generation in HTS composite over a wide current sharing range is calculated based on power-law E — J characteristics with temperature dependence of the n-value and critical current density. Thermal properties of the HTS composite and coil sections were measured and compared with estimated values based on data for individual coil components and the fill factor of the coil construct. The effect of replacing the complex coil winding structure with an effective continuum was investigated by examining the normal zone temperature profiles and minimum quench energy (MQE). With reducing operating temperature from 77 K to 30 K, MQE reduces correspondingly from 30 J to 15 J. Simulation results are found in satisfactory agreement with experimental results from a test coil wound with PbBi2223 tape. [ABSTRACT FROM AUTHOR]

The quench characteristics of Cu–Ni sheathed MgB2 superconducting monofilament tape were studied experimentally. We have investigated the stabilities i.e. minimum quench energy (MQE), normal zone propagation velocity vp at 4.2 K. Sample tape was triggered a local normal zone with a heater. By measuring the MQE and vp of MgB2 tape, we derived the dependence of MQE and vp on transport current and magnetic field. In addition, minimum propagation current was also obtained from the transport current dependence of vp. [Copyright &y& Elsevier]

• It is found that in the experimental measurement of MQE of short YBCO conductor, different heater configurations can results in different values of MQE. • It is found when viewed as functions of hot spot temperature, the quench characteristics of short YBCO conductors, including normal zone propagation velocity (NZPV), normal zone size and the temperature rising rate of hot spot, are not sensitive to heater configurations, which is useful characteristic for the formulation of quench detection schemes. Based on a fully two-dimensional (2D) electrothermal model, the quench propagation characteristics of short superconducting YBa 2 Cu 3 O 7-x conductors (AMSC and SuperPower), including the minimum quench energy (MQE), normal zone propagation velocity (NZPV) and hot spot temperature rising rate, are studied by numerical simulations in this paper. It is found that different heater configurations, such as the size of heater and the duration of heat pulse, can result variations of the MQEs and NZPVs. During the quench propagation processes, the NZPV and the normal zone length (L NZ), when viewed as functions of the hot spot temperature T peak , i.e., NZPV(T peak) and L NZ (T peak), are not sensitive to the heater configurations for relatively higher operating temperature from 50 K – 70 K. For both AMSC and SuperPower's YBCO conductor, the simulation results show that the hot spot temperature rising rate d T peak /dt, as a nearly-linear function of T peak , is almost not affected by heater configurations for a given fixed operating temperature in the regime 30 – 70 K. For a fixed operating temperature in the regime 30 – 50 K, the temperature rising rate of SuperPower's conductor can reach 1000 K/s ~ 6000 K/s as T peak rising from ~110 K to 300 K, which makes it challenging to experimentally determine the NZPV prior the moment T peak reaches the temperature limit 300 K. The relations L NZ (T peak) obtained for SuperPower's conductor can provide information for the selection of reference voltage employed to determine the NZPV. [ABSTRACT FROM AUTHOR]