Minimum Quench Energy Research Articles

Modeling of Quench Behavior of YBa2Cu3O<inline-formula> <tex-math notation="LaTeX"> $_{7\text{-}\delta}$</tex-math> </inline-formula> Pancake Magnets and Distributed-Temperature-Sensing-Based Quench Detection for Operating Temperature 30–77 K

A two-dimensional/three-dimensional (2-D/3-D) mixed electrothermal model is proposed for the simulation of quench behavior of high-temperature superconducting (HTS) pancake magnets, where a 2-D electrothermal model is proposed to simulate the YBa2Cu3O $_{7\text{-}\delta}$ (YBCO) subcoil and is coupled with the remaining parts of the YBCO magnet, which are treated as 3-D homogeneous coils. For operating temperature from 30 to 77 K, the quench behavior of four YBCO pancake coils (two Kapton-insulated coils and two TiO2-insulated coils) are simulated. Thermal equilibrium states are found for both Kapton- and TiO2-insulated coils. The thermal conductivity of insulating materials (Kapton, TiO2) significantly affects the equilibrium temperature profiles (ETPs) and the minimum quench energy (MQE), especially for relatively high operating temperature (e.g., 65–77 K). The distributed-temperature-sensing-based (DTS-based) quench detection criterion can be established on ETPs. The effect of the thickness of insulating materials on ETPs and MQEs is relatively weak, especially under relatively low operating temperature. The key parameters of ETP-based quench detection criterion, such as the reference temperature, the peak temperature, and the minimum normal zone size, are obtained for the operating temperature from 30 to 77 K.

A Numerical Adiabatic Model for the Quench Behavior Analysis of the Ag-Matrix Bi-2212 Round Wire

To study the quench behavior of the Bi-2212 round wire as a promising superconductor for future fusion reactor coils and high-field magnets, a numerical adiabatic model has been developed at the Institute of Plasma Physics, Chinese Academy of Sciences. The model is in 1-D and the partial differential equation is solved with the implicit method. Quench energy is simulated by introducing heat in a section of the wire, and the temperature and voltage are calculated as the function of time and space. The minimum quench energy and normal zone propagation velocity were calculated at different conditions. The results from the model were compared with analytical solution and experiment data. The analysis and discussion are presented in this paper.

Development of design for large scale conductors and coils using MgB2 for superconducting magnetic energy storage device

MgB2 wires are commercially available, and their superconducting characteristics have been continuously developed in the last decade. The relatively high critical temperature of these wires has attracted the attention of researchers, especially in the field of superconducting magnetic energy storage (SMES) coil applications in terms of its relatively high critical temperature, as it enables the use of liquid hydrogen for cooling the coils. The sensitivity of multi-filament MgB2 wires to bending strain makes the design of large-scale conductors and coils for an SMES system technologically difficult, and the careful investigation of the applied strains during manufacturing is required. Two-conventional methods have been introduced for the fabrication of the coils: wind-and-react (W&R) and react-and-wind (R&W). These methods have been demonstrated to be suitable for the production of large-scale MgB2 magnets to maximize the coil performance. The W&R and R&W methods have been successfully applied to the designs of conductors and coils, and small W&R test coil fabrication, as well as stability demonstrations are performed in this study. Our study is the first to demonstrate the feeding of hundreds of amperes of transport current using multifilamentary MgB2 wires at around liquid hydrogen temperature in the practical background magnetic field of 2 T. The minimum quench energy and normal zone propagation velocity are also experimentally investigated for the protection of the actual coils for SMES application.

Experimental Study of Normal Zone Propagation in the Short Sample of Bi-2223/Ag/AgMg Tape in Two Different Cooling Modes

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.

Quench energy studies in ITER conductors for different magnetic field perturbations with Jackpot and THEA combined models

The electromagnetic–thermal models for the cable-in-conduit conductors (CICCs) JackPot-ACDC and THEA (thermal, hydraulic and electric analysis of superconducting cables) are combined to predict the stability of ITER central solenoid conductors. The combination of both models allows the prediction of the effect of any type of magnetic field perturbation in time, relevant for the magnet coils during the plasma operation scenario of the reactor. At present, there is no experiment for testing the stability of the ITER Nb3Sn conductors under such conditions. Only limited experimental data on minimum quench energy (MQE), defining the conductor stability, are available but the time and magnetic field amplitude settings are completely different from the actual ITER operating conditions. Nevertheless, such tests are useful as a basis to calibrate and benchmark the codes. The JackPot-THEA combination allows us to determine the MQE for any magnetic field change in time and to fully describe the involved electromagnetic phenomena in strand-level detail in terms of local power dissipation and (peak) electric field along all strands. Thermally, the computation is still on a global scale for identifying the quench initiation and propagation. The predictions from the combined codes are in good agreement with the experimental results and provide a solid basis for extrapolative scaling of the stability of CICCs under plasma operating conditions.

A Fast Quench Protection System for High-Temperature Superconducting Magnets

For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of high-temperature superconductors (HTS) is unavoidable. Due to the high minimum quench energy in HTS these coils are much more difficult to protect against quenches using conventional methods, such as quench heaters or coupling loss induced quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here, a method named E 3 SPreSSO (External Energy Extraction Symbiotic Protection System for Series Operation) is proposed that allows for fast energy extraction in HTS magnets. The E 3 SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, overcurrent or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore, it is possible to use relatively cost-efficient and robust Nb-Ti or possibly MgB 2 (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E 3 SPreSSO units themselves.

Stability analysis on Nb3Sn sample conductor of CFETR central solenoid model coil

The magnet system of China fusion engineering test reactor (CFETR) includes toroidal field, central solenoid (CS) and poloidal field coils. The design and fabrication of CS coil are most significant and challenging for China due to the lack of experience. As the core technique of CS coil, cable-in-conduit-conductor (CICC) has been chosen to ITER CS conductor with the short twist pitch (STP) cable pattern. STP cable pattern has been demonstrated to avoid the performance degradation of conductor after electromagnetic cycling and warm-up-cool-down thermal cycles during operation. For qualifying the manufacturing process and performance of conductor, two short sample conductors were manufactured at ASIPP and tested at Swiss Plasma Center. Performance tests include DC test, Tcs, AC loss and MQE (Minimum Quench Energy) measurements. This paper is mainly about the stability analysis, and the energy margins of the conductor at various operation conditions are investigated with test data and model simulation.

Analysis of the Self-Protection Characteristics of a 1.5 T Bitter-Like HTS Magnet Operated at 65 K**Supported by the Fundamental Research Funds for the Central Universities under Grant No 2018MS004.

We present a conceptual configuration of a high-temperature superconducting (HTS) magnet made from REBCO (Re=Rare Earth, B=Barium, C=Copper, O=Oxide) annular plates, called a Bitter-like HTS magnet, which can operate in persistent current mode without joint resistance and can be excited by a flux pump and without current leads and a persistent power supply. An REBCO annular magnet which can generate 1.5 T corresponding to the operating current density 80% of critical current density of the magnet at an operating temperature of 65 K is conceptually designed. Then the thermal stability of the magnet is numerically simulated by Comsol software. When a piece of REBCO annular plate quenches, the maximum released energy is its stored energy because each REBCO annular plate in the Bitter-like magnet is in parallel. To calculate the stored energy in the REBCO annular plate, the inductance of every annular plate, including self-inductance and mutual inductance, is calculated. Compared with the minimum quench energy (MQE) and stored energy in one REBCO annular plate, the stored energy in one REBCO annular plate is always smaller than the MQE, and the REBCO annular plate will not be damaged even though the stored energy in the REBCO annular plate is fully released, which indicates that this 1.5 T Bitter-like magnet has the property of self-protection.

Quench Characteristics Comparison Between Solid Nitrogen and Conduction Cooled REBCO Coil Under Thermal Disturbance and Over Current Pulse

In power system application of high temperature superconducting (HTS) equipment, large amount of heat caused by thermal disturbance or over current during sudden electric interruptions will endanger the thermal stability of HTS devices. However, solid nitrogen (SN2) with large heat capacity can enhance the thermal stability of HTS magnets. In this paper, the quench characteristics of SN2 and conduction cooled REBCO coil under thermal disturbance and over current pulse has been investigated at 60 K. For the thermal disturbance experiment, the minimum quench energy, longitudinal and transverse normal zone propagation velocities in SN2, and conduction cooled system are compared and discussed. The strain response property of the coil from quench to complete cooled down after power off during the quench process has also been preliminarily discussed. What is more, the accumulated peak voltage and strain of the coil during the over current pulse test has been studied. These results show that SN2 can help to enhance the thermal stability of REBCO coil under thermal disturbance and over current pulse.

Improvement of stability of Nb3Sn superconductors by introducing high specific heat substances

High-Jc Nb3Sn conductors have low stability against perturbations, which accounts for the slow training rates of high-field Nb3Sn magnets. While it is known that adding substances with high specific heat (C) into Nb3Sn wires can increase their overall specific heat and thus improve their stability, there has not been a practical method that is compatible with the fabrication of long-length conductors. In this work, we put forward a scheme to introduce such substances to distributed-barrier Nb3Sn wires, which adds minimum difficulty to the wire manufacturing process. Multifilamentary wires using a mixture of Cu and high-C Gd2O3 powders have been successfully fabricated along this line. Measurements showed that addition of Gd2O3 had no negative effects on residual resitivity ratio or non-Cu Jc, and that flux jumps were remarkably reduced, and minimum quench energy values at 4.2 K, 14 T were increased by a factor of three, indicating that stability was significantly improved. We also discussed the influences of the positioning of high-C substances and their thermal diffusivity on their effectiveness in reducing the superconductor temperature rise against perturbations. Based on these results, we proposed an optimized conductor architecture to maximize the effectiveness of this approach.

Effect of the local defects induced by bending strain on the quench properties for YBCO tapes

The effect of local defects on the quench properties for YBCO tapes after applying bending strain was investigated at self-field in 77 K. The minimum quench energy (MQE) was related to the position of defects in the tape and the smallest MQE appears where the region of the defects existed in the position of the heater at the same transport current. The normal zone propagation velocity (NZPV) was related to the size and quantity of the regions of defects. The more defects were in the tape, the faster the normal-zone propagation velocity.

Experimental study of quench in a short sample of Bi-2223/AgMg tape in a conduction-convection cooling regime

Superconducting magnets based upon high temperature superconductors (HTSs) are more stable than low temperature superconductors (LTSs). This means that the minimum quench energy (MQE) of a HTS is higher than that of a LTS. However, disturbances such as flux jump, wire movement and epoxy cracks can cause a thermal runaway. In this case, HTSs are vulnerable because of the low normal zone propagation velocity (NZPV) thus HTS magnets are not self-protecting. To design a safe operating point for such magnets, quench characterization and the cooling mode are important. In this article, the normal zone propagation evolution of a short sample of Bi-2223/AgMg high temperature superconducting tape has been investigated by applying localized heat pulses. Experiments were carried out based on cryogenic stabilization in N2 vapor. To enhance the thermal stability, the superconductor sample is mounted on a copper plate which is immersed in liquid nitrogen up to the given height. By increasing the current, we measured the rate of decrease of the MQE, the superconducting stability factor, the rate of increase NZPV, and the protection parameter against quench.

Analysis of ITER NbTi and Nb3Sn CICCs experimental minimum quench energy with JackPot, MCM and THEA models

Cable-in-conduit conductors (CICCs) for ITER magnets are subjected to fast changing magnetic fields during the plasma-operating scenario. In order to anticipate the limitations of conductors under the foreseen operating conditions, it is essential to have a better understanding of the stability margin of magnets. In the last decade ITER has launched a campaign for characterization of several types of NbTi and Nb3Sn CICCs comprising quench tests with a singular sine wave fast magnetic field pulse and relatively small amplitude. The stability tests, performed in the SULTAN facility, were reproduced and analyzed using two codes: JackPot-AC/DC, an electromagnetic-thermal numerical model for CICCs, developed at the University of Twente (van Lanen and Nijhuis 2010 Cryogenics 50 139–148) and multi-constant-model (MCM) (Turck and Zani 2010 Cryogenics 50 443–9), an analytical model for CICCs coupling losses. The outputs of both codes were combined with thermal, hydraulic and electric analysis of superconducting cables to predict the minimum quench energy (MQE) (Bottura et al 2000 Cryogenics 40 617–26). The experimental AC loss results were used to calibrate the JackPot and MCM models and to reproduce the energy deposited in the cable during an MQE test. The agreement between experiments and models confirm a good comprehension of the various CICCs thermal and electromagnetic phenomena. The differences between the analytical MCM and numerical JackPot approaches are discussed. The results provide a good basis for further investigation of CICC stability under plasma scenario conditions using magnetic field pulses with lower ramp rate and higher amplitude.

The Use of a Winding Model Instead of Effective Continuum Model Can Lead to a Drastic Reduction of MQE in Superconducting Coils

Thermal stability is an essential parameter for coil design. Previous measurements in an MgB2 solenoid have revealed a change in trend in the minimum quench energy (MQE) dependence on j = I/I., showing lower values than expected for operative current close to the critical current (j ~ 0.90). The obtained MQE is comparable to the one predicted by analytical models in a single tape (1D) being of the order of 1-10 mJ, which indicates that propagation across winding and layers (3D) is not taking place. This reduction of MQE is not obtained in the effective continuum model, because the different turns and layers are not reproduced. Obtaining 1D propagation depends on the ratio between the thermal conductivity of the conductor and insulation and on the cooling conditions at the boundary layers. A numerical model of a superconducting solenoid with full representation of the winding is used to study MQE as a function ofj (0.6-0.99). The quench is triggered applying heat pulses of 40 ms in a region of 4 mm of the outer layer of the coil. The effect of changing the cooling boundary conditions of the coil from adiabatic to isothermal is also investigated.

Numerically Thermal Stability Analysis on a Geometrically Symmetrical Strand Fabricated by 2G Wires in Liquid Helium Temperature

Due to its excellent j c (B) performance at low temperatures, the second generation (2G) high-temperature superconducting (HTS) REBCO wire is promising for high-field applications. The thermal stability of a strand consisting of 2G wires operating at low temperatures is an important issue with increasing current density at high magnetic field. The paper focuses on the thermal stability of geometrically symmetrical strands under background direct current (dc) magnetic field of 6 T in liquid helium temperature by numerical method. The strand with copper sheath consists of 80 stacked 2G wires. The thermal stability of the strand is accurately analyzed based on the analytical dependence of the critical current density on temperature and magnetic field as well as its orientation to wide surface of 2G wire. By using the helium heat transfer coefficient, the minimum quench energy and the quench propagation velocity of the strand in liquid helium temperature are calculated and compared with those in the adiabatic conditions, the results are useful for application of the strand in high magnetic field at low temperature.

Quench Characteristics of a 2-kA REBCO Quasi-Isotropic Superconducting Strand in Liquid Nitrogen

High-temperature superconducting strand with high current capacity is expected to have widely potential applications transferring electric power and superconducting power devices since it is easy to insulate to avoid point charging. Quench characteristics of a 2-kA quasi-isotropic superconducting strands made of REBCO tape with copper sheath in liquid nitrogen (LN2) were investigated numerically and experimentally in this paper. The minimum quench energy and quench propagation velocity of the superconducting strand were simulated and measured. The simulation results are in very good agreement with the experiment. Due to high current density and quasi-isotropic critical current in magnetic field, this kind of superconducting strand has potential application in high-current transmission and high-field magnets.

First Cold Powering Test of REBCO Roebel Wound Coil for the EuCARD2 Future Magnet Development Project

EuCARD-2 is a project partly supported by FP7-European Commission aiming at exploring accelerator magnet technology for 20 T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high field magnets in the USA and Japan. EuCARD-2 focuses, through the work-package 10 “Future magnets,” on the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, for a 5 T stand-alone dipole of 40 mm bore and about 1 m length. After standalone testing, the magnet will possibly be inserted in a large bore background dipole, to be tested at a peak field up to 18 T. This paper starts by reporting on a few of the highlight simulations that demonstrate the progress made in predicting: dynamic current distribution and influence on field quality, complex quench propagation between tapes, and minimum quench energy in the multitape cable. The multiphysics output importantly helps predicting quench signals and guides the development of the novel early detection systems. Knowing current position within individual tapes of each cable we present stress distribution throughout the coils. We report on the development of the mechanical component and assembly processes selected for Feather-M2 the 5 T EuCARD2 magnet. We describe the CERN variable temperature flowing helium cold gas test system. We describe the parallel integration of the FPGA early quench detection system, using pickup coils and temperature sensors, alongside the standard CERN magnet quench detection system using voltage taps. Finally we report on the first cold tests of the REBCO 10 kA class Roebel subscale coil named Feather-M0.

Analysis of the ITER central solenoid insert (CSI) coil stability tests

At the end of the test campaign of the ITER Central Solenoid Insert (CSI) coil in 2015, after 16,000 electromagnetic (EM) cycles, some tests were devoted to the study of the conductor stability, through the measurement of the Minimum Quench Energy (MQE). The tests were performed by means of an inductive heater (IH), located in the high-field region of the CSI and wrapped around the conductor. The calorimetric calibration of the IH is presented here, aimed at assessing the energy deposited in the conductor for different values of the IH electrical operating conditions. The MQE of the conductor of the ITER CS module 3L can be estimated as ∼200J±20%, deposited on the whole conductor on a length of ∼10cm (the IH length) in ∼40ms, at current and magnetic field conditions relevant for the ITER CS operation. The repartition of the energy deposited in the conductor under the IH is computed to be ∼10% in the cable and 90% in the jacket by means of a 3D Finite Elements EM model. It is shown how this repartition implies that the bundle (cable + helium) heat capacity is fully available for stability on the time scale of the tested disturbances. This repartition is used in input to the thermal-hydraulic analysis performed with the 4C code, to assess the capability of the model to accurately reproduce the stability threshold of the conductor. The MQE computed by the code for this disturbance is in good agreement with the measured value, with an underestimation within 15% of the experimental value.

Evaluation of inductive heating energy of ITER toroidal field conductor by calorimetry

The influence of a fast electromagnetic perturbation, such as plasma disruption, on the ITER toroidal field (TF) coil conductor was studied. When a fast magnetic field change is superimposed, the TF conductor is inductively heated by internally generated eddy currents. To measure the inductive heating (IH) energy amount by calorimetry, an IH experiment using short TF conductor samples with length of 20 cm was performed in a liquid He bath. The sample components used were a TF conductor, TF jacket and a TF conductor cable. A 60-turn, single layer solenoid coil was installed around each sample as an IH coil. Also, the Joule heat of the IH coil was solely measured to subtract its thermal contribution from the other samples. A 1 kHz sinusoidal AC current was applied to each IH coil, changing the current amplitude. The heat generated in the samples, including the IH coil, was eventually absorbed into the liquid He, and the liquid He was then vaporized. Thus, the heat amount was measured by a He level sensor inside a gas collection cylinder attached above the sample. The validity of the experimental results was confirmed by comparing them with computation results of the IH energy of the samples with a computation model. Also, the consumed energy was calculated from the measured waveforms of the applied AC voltage and current to the samples. As the result, the measured and calculated IH energy were found to be in good agreement. Finally, based on the results of the experiment, the minimum magnetic field strength, which triggers quench of the TF conductor by fast dumping like plasma disruption, was evaluated using estimated TF conductor minimum quench energy.

Transient stability of NbTi Rutherford cables for energy storage magnet applications

Stability and quench behavior against transient perturbation expected during operation of a fast cycling energy storage magnet is an important issue for its design and safe operation. Understanding of thermal stability in terms of minimum quench energy (MQE) of a superconducting cable under specific operating scenario is of primary importance for its magnet application. Process of current redistribution from quench strand to adjacent strands depends on inductive coupling and has influence on quench development in the cable. The electrodynamic and thermal behavior of a ten-strand Rutherford-type cable for SMES program in the centre is studied numerically in the framework of discrete network modeling. Influence of several parameters such as uncertainties of inter-strand transverse and adjacent resistance, cooling conditions with liquid helium, etc. on MQE and quench behavior of Rutherford cable is discussed in this paper.