Quench Phenomena Research Articles

Modelling and analysis of quench in the 15-kA HTS conductor

High Temperature Superconductors (HTS) are very promising materials for possible application in future fusion magnets, with significant R&D progress on HTS conductors in recent years. However, since geometric and thermo-physical characteristics of HTS and LTS conductors differ significantly, some doubts have arisen if the approaches successfully used in numerical simulations of the thermal–hydraulic behavior of LTS conductors would be sufficient also for HTS, particularly in cases when fast transient processes (such as e.g. quench) are considered. In order to provide data for better understanding of the quench phenomenon in HTS conductors as well as for testing different numerical approaches and proper tuning of the numerical codes, a dedicated experimental campaign (Quench Experiment) was carried out at the SULTAN test facility within the international collaboration between the EUROfusion consortium and China. Our present study is a part of the work on analysis and interpretation of the data collected during this experiment. Simulations of the chosen experimental run were performed using two THEA models with different levels of complexity. Uncertain model parameters (thermal resistances and copper RRR) were explored across a wide range. Our goal was to identify the possibly simple model that accurately reproduces the experimental results.

Fault current limiter based on high temperature superconductors

High Temperature Superconductors (HTS) made the Superconducting Fault Current Limiter (SFCL) a reality in power electric grids. Resistive SFCL, which is the subject of this article, is based on a unique property of superconductors to quench from a non-dissipative to a high dissipative state above a given current. SFCL is an attractive response to the poorly solved problem of fault currents in power electric grids and makes it possible to enhance the security and quality of electricity, something that matters more than ever. Liquid nitrogen cryogenics – which is possible thanks to HTS- makes the cryogenics user friendly. In-field SFCL operations confirm this. Second generation (2 G) HTS materials or Coated Conductors suit well to SFCL. Due to its high interest, SFCL has been the subject of a great deal of research and development. In terms of Technology Readiness Level (TRL) it reaches 8 with several in grid test experiences.Here a short history of SFCL is presented with a highlight about Curl 10, Ampacity and SuperOx devices. The two major locations in the grid are reported: grid coupling and feeder protection. The quench phenomena is described in a bit more detail before the basic design (length and cross section) is presented. The design is primarily thermal, considering two extreme operations: fault with very high prospective current (clear short-circuit) and fault with prospective current close to the minimum runaway current along the length. This operation is called the hot spot one. It is due to the intrinsic variation of the critical current along the length and to the low Normal Zone Propagation Velocity (NZPV). The cost of the superconducting conductor is given, showing no bottleneck for an economic development. All the more it is still possible to lower the cost with some developments. This article ends with two real advances presently underway: Current Flow Diverter (CFD) and Sapphire substrate superconducting 2 G tape. CFD aims to increase the NZPV, to still further secure the operation and to reduce the conductor cross section. The use of sapphire substrates allows to reduce significantly the length of the design.

Time-Frequency Domain Monitoring Method for the Fault of HTS HVDC Systems Based on AI Classifiers

Since high-temperature superconductor (HTS) based HVDC systems are affected by temperature and cooling system performance, noise, the monitoring system which can classify the temporal disturbance and anomalies must be developed to ensure stable system operation. To solve this, it needs anomaly detection that accounts for system sensitivity and is able to continuously manage the response to disturbances. In this paper, we propose an integrated solution for fault severity diagnosis and anomaly detection colorred with AI based reflectometry. Anomalies such as the quench phenomenon can be detected through the anomaly score based on the reconstruction error calculated through the proposed autoencoder(AE) method. After anomaly detection, a fault classification algorithm based on the convolutional neural network (CNN) using a 2D image of a converted reflected signal through the proposed image processing was conducted. Based on the signal acquired from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$7 m$</tex-math></inline-formula> length 1st generation 22.9 kV/50 MVA HTS cable, PSCAD simulation was utilized to construct a long-distance line model and verified the performance of the proposed algorithm.

The upgraded quench protection system for main quadrupoles in the LHC

The protection of superconducting magnets is a very important issue and demanding challenge in the LHC and other superconducting accelerating facilities. The quench phenomenon can destroy components of the accelerator, and therefore this digital system was designed, implemented, tested, and installed near each superconducting magnet in the LHC tunnel. The quench detection principle relies on the extraction of resistive voltage by compensation of the inductive part of the voltage. This article presents briefly the architecture applied to the design and the validation of the FPGA-based quench detector for the main quadrupoles of the LHC. The article focusses on digital design with the use of FPGA by VHDL coding and on the verification by simulation. The design is a replacement for the old detection system.

Benefits of high-energy varistors in breakdown and fast discharge units

Tokamak coils require protection systems to extract the stored magnetic energy without breaking the power supply circuit. This is more critical in superconducting coils, especially due to quench phenomena. This protection can be simply obtained by fast discharge units (FDUs), able to insert proper resistor banks in the coil circuit. Similarly, resistive switching network units (SNUs) are the standard method to initiate plasma in tokamak. The use of varistors instead of linear resistors can introduce several benefits for the tokamak operations, including the possibility to implement in a single unit both the SNU and the FDU functions. These principles are descried in this paper with reference to their applications in the DTT facility, reporting some examples of the possible and selected parameters. Nevertheless, the proposed approaches, the developed theory and the obtained results can be adapted to any tokamak and nuclear-fusion project.

Multi-physics quench simulation of no-insulation HTS insert coils with high background magnetic field

Compared with traditional insulated High Temperature Superconducting (HTS) coil, no-insulation (NI) HTS coil has higher thermal stability and self-protection capability, so that is considered as an important way to generate high steady-state magnetic field. This paper focuses on the experimental phenomena that mechanical damage always occurs in NI coils during quench with high background field. A multi-physics quench simulation model is established for NI insert coils, which contains a 2-d axisymmetric partial element equivalent circuit (PEEC) model for electromagnetic calculation and two axisymmetric finite element models for thermal and mechanical analysis. Based on these models, we analyzed the electromagnetic, thermal and mechanical phenomena of insert coils during quench propagation and recovery. The simulation results show that mechanical damage may occur in the outer superconducting zone near the normal zone in no-insulation coils during quench, and thermal strain caused by temperature rise during quench may exacerbate mechanical damage. Meanwhile, quench at different single-pancake coils has different effects on the mechanical performance of the entire insert coils. Based on the electromagnetic simulation results, we also analyzed the time delay of the traditional terminal voltage quench detection method and its causes. This study analyzed the multi-physics quench phenomenon of no-insulation HTS insert coils. And the results imply that hoop strain will increase to the critical strain due to high magnetic field and current redistribution caused by radial current shunt during quench, resulting in mechanical damage. Additionally, radial current shunt and induced voltage will retard quench propagation velocity, resulting in the time delay in terminal voltage quench detection.

The Study on the Quench Helium Release Process of HFRS Superconducting Magnet

The quench phenomenon of the accelerator superconducting magnet may occur in operation, which will cause the liquid helium in the cryostat to evaporate rapidly and release in the atmosphere. High-pressure helium will result in serious damage on significant components in the transmission line, and the released helium in the tunnel will lead to the ODH (Oxygen Deficiency Hazard), threatening the safety of operators. In this paper, the species transport model was used to study the 2D helium discharge process of fragmentation separator in HIAF (High-Intensity heavy-ion Accelerator Facility) by using the platform of computational fluid dynamics software FLUENT. To verify the effectiveness of the species transport model for the FLUENT in simulating the mixing jet process of different components, a 2D FLUENT simulation results of the LHC helium release process was compared with the experimental results and the 3D OpenFOAM simulation results. The results show that the species transport model based on FLUENT could predict the helium release process effectively. Then the distributions of helium concentration, temperature, and velocity in the HFRS (High energy FRagment Separator) tunnel were studied and obtained by the present work. Based on the above analysis, a reasonable design scheme of the accelerator superconducting magnet relief system can be accomplished for HFRS.

DC Characterization of a Low-Field Nb3Sn Prototype Conductor for a DEMO TF Coil

A Low Field W&R (Wind and React) conductor, developed in the frame of the conceptual design studies for the Toroidal Field (TF) coils of DEMO, has been designed to be constituted of a small number of superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands and a high number of stabilization copper wires. It has been extensively characterized at the SULTAN facility at Swiss Plasma Center (SPC) in February 2021. The conductor has been operated up to its target current, 70.8 kA, and characterized up to a background magnetic field of 10.78 T. The test program included AC loss measurements, current sharing temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_cs</i> ) and critical current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> ) measurements before and after cyclic loading. Critical temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> ) measurements were performed on the virgin conductor at the beginning and at the end of the test campaign. In this work we are focusing on the DC characterization, while the AC measurements analysis will be the object of a following work. Concerning DC tests, premature quench phenomena prevented from operating the conductor at the target current – field conditions. Nevertheless, at lower currents <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_cs</i> stability was observed, with no performance degradation due to cycling. The present paper investigates these results and tries to give an explanation through measurements and tomographic analysis. Furthermore, the achieved strain distribution in the conductor, obtained by means of inductive measurements analysis, will be shown. The implications of the design approach on the performance, based on the outcome of such tests, are discussed.

Design of a magnet to study quench propagation in a Cable-In-Conduit-Conductor filled with stagnant superfluid helium

In the dark matter Axion research context, the MADMAX project acts as a figurehead in the physics research field. The goal of the project is to discover axion as dark matter. For this, it is necessary to design and manufacture a dipole, composed of 18 coils, that generates a Figure of Merit of 100 T2m 2. The MADMAX coils have several specific features though, as the use of Cable-In-Conduit-Conductor (CICC) with a copper profile that serves as thermal stabilizer and the use of stagnant superfluid helium inside the CICC conduit. With a 28 mm2 helium cross-section and a conductor of several hundred meters before reaching the helium bath, the quench dynamics appear then as a challenge of the design phase. To experimentally investigate the quench propagation in the MADMAX coils, we designed a MADMAX-like solenoidal prototype based on numerical simulations made with THEA® called MACQU (MAdmax Coil for Quench Understanding). This numerical study allowed analysing the physics behind the quench phenomenon and define the relevant current range for the experimental quench studies. Nevertheless, as THEA® has never been used for a CICC filled with superfluid helium, the results will have to be benchmarked by the quench testing campaign on MACQU. The different calculations made with THEA® show that the quench propagation is divided into two different phases: after the initiation, the propagation is at a constant speed of around 5 m/s, followed by an acceleration phase where the propagation speed reaches 40 m/s, at 17 kA. Among the different possible phenomena, we have found that the friction forces term, as defined in the THEA code, are responsible for this two-phase propagation because they initiate the pre-heating of the magnet before the quench, reducing then the local temperature margin.

Multi-field coupled effect of thermal disturbance on quench and recovery characteristic along the hybrid energy pipe

In a novel high temperature superconducting (HTS) hybrid energy pipe, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain high energy transmission efficiency. When the pipe is exposed to thermal disturbance, the protective medium, liquid nitrogen (LN2), can restrain the quench phenomenon by boiling heat transfer. In order to analyze the multi-field coupled effects of thermal disturbance on the quench and recovery process of the hybrid energy pipe, a one-dimensional quench model is originally proposed in this paper. The model can reflect the intricate interaction of fluid dynamics, boiling heat transfer and current sharing. The results indicate that the high temperature region moves towards the upstream direction in the recovery process. There are three different characteristics: thermal stable zone, quench controllable zone and quench propagation zone. The critical quench energy Qqc is 18% of the critical recovery energy Qrc and the critical quench distance lqc is 9 times as long as the critical recovery distance lrc, independent of the operation conditions. The Qqc and lqc will results in the longest recovery process of the pipe. The pulse duration hardly affects the quench and recovery characteristics. The critical equilibrium current Iec is a constant value of 1800 A, independent of the heat pulse parameters. The Iec will cause the infinite recovery time, which is harmful for the hybrid energy pipe. These rules are significant for the stable operation and design of the hybrid energy pipe. The proposed model can reflect the multi-field strong coupled effect of the thermal disturbance on the quench of system, which fulfils the fast prediction of the quench and recovery behavior.

Transient modeling of quench and recovery of LNG-HTS hybrid energy transmission system based on multi-field coupled analysis

• LNG cold energy is utilized for the operation of HTS cable. • A 1-D model with electromagnetic, thermal and flow analysis is originally proposed. • The complete quench and recovery characteristics can be obtained. • Under a specific condition, the quench of the system can be recovered by itself. • The recovery time has a power law relation with the velocity of liquid nitrogen. In a novel high temperature superconducting (HTS) hybrid energy transmission system, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain very high energy transmission efficiency. The liquid nitrogen (LN 2 ) is used to provide a low temperature environment and can also restrain the quench phenomenon as a protective medium. As the safety of the system is the biggest concern, a one-dimensional model with the quasi static state method is originally proposed in this paper to analyze the quench and recovery behavior. The model firstly introduces the electromagnetic analysis into the thermal and flow analysis, combining intricate interaction of phase change, fluid flow, heat transfer and current sharing. In this paper, the complete quench and recovery characteristics can be obtained when the system is subjected to the default current or thermal disturbance. The results indicate that under a specific condition, the quench of the system can be recovered by itself including different stages, going through the cooling process of film boiling, nucleate boiling, transient boiling and forced convection in turn. The recovery time caused by the default current is much longer than that caused by thermal disturbance and it has a power law relation with the velocity of LN 2 . For the quench process caused by the default current, the maximum temperature of the system decreases with the increase of LN 2 velocity. For the thermal disturbance, the maximum temperature almost keeps constant. The proposed model can predict the quench and recovery behavior in advance, which is significant for the stable operation and design of the hybrid energy transmission system.

Effect of superconducting magnet structure on quench characteristics

ABSTRACT In the design process of MRI magnets, the study of quench phenomenon is of great significance to the operation of superconducting magnets. In this paper, the quench characteristics of 1 T symmetric magnet and asymmetric magnet are simulated and analysed by using three-dimensional finite element software OPERA. The modelling process and algorithm of simulation are introduced in detail. The critical current density of NbTi superconducting material is set by looking up table variables preset by software. Through simulation and analysis, the changing principles of the current and resistance of the superconductor coil, which are important physical quantities of the two kinds of magnet structures in quenching are obtained. Three-dimensional simulation graphics are more conducive to observing the propagation speed of quench in different directions. It is concluded that although the DSV (diameter sphere volume) of asymmetric magnet is larger than that of symmetric magnet, the damage of asymmetric magnet is more serious than that of symmetric magnet during the quench.

Quasi-3D Discretization of Thermal Hot-Spot Propagation in Superconducting Models

To deal with the multi-scale nature of the quench propagation problem in superconducting magnets, this work presents a quasi-three-dimensional (Q3D) approach combining a two-dimensional finite-element method (FEM) in the transversal cross-section of the magnet for resolving the geometrical details, with a one-dimensional spectral-element method based on orthogonal polynomials in longitudinal direction for accurately and efficiently representing the quench phenomena. The Q3D formulation is elaborated and the idea is illustrated on a thermal benchmark problem. Finally, the method is validated against a conventional 3D simulation carried out by a commercial software. In terms of computational efficiency, it is shown that the proposed Q3D approach is superior to the conventional 3D FEM.

Modeling of Thermal Quench in Superconducting RF Cavities

Superconducting radio frequency (SRF) cavities are often limited by thermal quench, which is an excessive electromagnetic heating that occurs in the high magnetic field area and expands thereafter forcing the cavity to lose its superconducting state. In this article, we demonstrate how the quench phenomena can be modeled using a coupled electromagnetic thermal analysis. The proposed model takes into account the nonlinearity of the material properties at cryogenic temperature and the effect of Kapitza resistance. The proposed approach is used to compute the thermal quench field of a 3.9-GHz 9-cell accelerating cavity, a 2.815-GHz deflecting cavity, and a 1.3-GHz 9-cell accelerating cavity. The computed values of quench field are in good agreement with the measured ones observed during vertical testing at 2 K. Without loss of generality, the proposed methodology can be applied to other cavity geometries.

Quench Phenomena in a Conduction-Cooled Fast-Ramping High Temperature Superconducting Magnet

A conduction-cooled HTS magnet was tested to produce an AC magnetic field up to 4 T for an adiabatic demagnetization refrigerator (ADR). Quench detection was conducted by measuring the voltages in the conductor, and the protection system was constructed with an external dump resistor. The magnet, which is equipped with extensive copper thermal drains, was conduction-cooled by a two-stage Gifford-McMahon cryocooler to approximately 6 K. The magnet succeeded to stably generate an alternating magnetic field between 0 and 3.5 T at a ramp rate of 229 mT/s without any pre-quench signs; however, in the case of a maximum 4 T experiment, a quench occurred, and the magnet was permanently damaged. The quench location was identified as the place where the highest perpendicular field from the magnet was generated. It is speculated that the already-formed normal zone before quench grows very fast during the dump process, and part of the magnetic energy is dissipated in this normal zone, causing the excessive temperature rise of the conductor. The detailed experimental results are presented and discussed.

Analysis and Design of Fast Discharge Resistor System Based on Forced-Air Cooling Method

The quench protection (QP) system is crucial to transfer the quench energy out within specific time when the quench phenomenon occurs in the superconducting magnet. The fast discharge resistor (FDR) system in the QP system is responsible for transferring and consumption of the quench energy. In large-scale superconductor test facility (LSTF), with extreme quench parameters concerning about the large current up to 90 kA, high inductance up to 2 H, and huge energy up to 8.1 GJ, the structure stability, heat controlling, and power feasibility of the FDR system are hard to be guaranteed. Therefore, a novel FDR system based on forced-air cooling method is put forward and discussed. The FDR system is with the characteristic of effectiveness protection, safety operating, and economic efficiency when compared with previous systems. In addition, based on the designed concept, the analysis and test process of the FDR system are carried out to testify the effectiveness and veracity. In particular, the structure stability of the shape deformation and cooling method of the temperature rise are analyzed. With the proof of simulation and testing results, the FDR system can serve for the QP system development of the new fusion device, the LSTF.

3-D Thermal-Electric Finite Element Model of a Nb3Sn Coil During a Quench

High field superconducting magnets for particle accelerators often exhibit premature quenches. Once a normal zone is generated within the conductor, the quench may propagate causing temperature and resistive voltage rise along the coil. The resulting thermal gradients can potentially cause new peak stresses that might exceed the tolerable limits, degrading the conductor. The computation of the strain state in the coils during quench then becomes of paramount importance for magnet design, and requires a complete three-dimensional (3-D) analysis of quench phenomena. The objective of this paper is to present the first multiphysics modeling activities towards a new full 3-D methodology for the analysis of magnet mechanics during quench. As a first step, a 3-D thermal-electric finite element model of a Nb 3 Sn superconducting coil is developed and explained here. The model uses direct coupled-field elements to solve the system of thermal and electrical equations. A solving algorithm has also been implemented in order to investigate the physics behind quench transients. The output from this model, built in ANSYS APDL, can be easily coupled in a later stage to a mechanical model in order to estimate the strain state in the coil windings. A very good agreement has been observed between the numerical results and experimental tests performed in individual superconducting cables and real superconducting magnets.

Detection of Local Temperature Change on HTS Cables via Time-Frequency Domain Reflectometry

High temperature superconducting (HTS) cables are drawing attention as transmission and distribution cables in future grid, and related researches on HTS cables have been conducted actively. As HTS cables have come to the demonstration stage, failures of cooling systems inducing quench phenomenon of the HTS cables have become significant. Several diagnosis of the HTS cables have been developed but there are still some limitations of the experimental setup. In this paper, a non-destructive diagnostic technique for the detection of the local temperature change point is proposed. Also, a simulation model of HTS cables with a local temperature change point is suggested to verify the proposed diagnosis. The performance of the diagnosis is checked by comparative analysis between the proposed simulation results and experiment results of a real-world HTS cable. It is expected that the suggested simulation model and diagnosis will contribute to the commercialization of HTS cables in the power grid.

Numerical thermal analysis of water's boiling heat transfer based on a turbulent jet impingement on heated surface

In this study, a numerical method for simulation of flow boiling through subcooled jet on a hot surface with 800°C has been presented. Volume fraction (VOF) has been used to simulate boiling heat transfer and investigation of the quench phenomena through fluid jet on a hot horizontal surface. Simulation has been done in a fixed Tsub=55°C, Re=5000 to Re=50,000 and also in different Tsub=Tsat−Tf between 10°C and 95°C. The effect of fluid jet velocity and subcooled temperature on the rewetting temperature, wet zone propagation, cooling rate and maximum heat flux has been investigated. The results of this study show that by increasing the velocity of fluid jet of water, convective heat transfer coefficient at stagnation point increases. More ever, by decreasing the temperature of the fluid jet, convective heat transfer coefficient increases.

Investigation of Effect of Ballooned Fuel Pins on Quenching Behavior: Design of Experiment and Preliminary Analysis

Heat transfer characteristics of intact fuel pins under reflood conditions have been extensively studied to understand the quench behavior of a typical pressurized water reactor (PWR). Overheating of fuel pins due to loss of nucleate boiling under exposed conditions causes the clad to balloon over large portions of the fuel pin length (up to 60%). The reflood behavior of ballooned fuel pins has been studied experimentally for ballooned heater pin configurations with an up to 15% ballooned length of the total length. Substantial changes in the reflood behavior are observed for a higher extent of the ballooned region. An experimental setup is thus being developed to study the effect of the large extent of the ballooned region (up to 60% of the total length) on the reflood behavior. The experimental setup employs a 5×5 matrix of indirectly heated fuel pins surrounded by 32 dummy fuel pins. The scaling analysis carried out for the design of the experimental setup is presented here. The nondimensional π terms pertaining to the quench phenomena have been conserved as compared to the typical PWR values. The evolution of some of the nondimensional π terms under reflood conditions has been discussed for simulations done with RELAP5 for ballooned as well as nonballooned test cases. Delayed quenching is observed in the extended ballooned fuel pins due to poor heat transfer in the ballooned region.