Quench Detection Research Articles

Anomaly detection at the European X-ray Free Electron Laser using a parity-space-based method

A novel approach to detect anomalies in superconducting radio-frequency (rf) cavities is presented, based on the parity space method with the goal to detect quenches and distinguish them from other anomalies. The model-based parity space method relies on analytical redundancy and generates a residual signal computed from measurable rf waveforms. The residual is a sensitive indicator of deviation from the model and provides different signatures for different types of anomalies. This new method not only helps with detecting faults but also provides a catalog of unique signatures, based on the detected fault. The method was experimentally verified at the European X-ray Free Electron Laser (EuXFEL). Various types of anomalies incorrectly detected as quenches by the current quench detection system are analyzed using this new approach.9 MoreReceived 28 February 2022Accepted 5 December 2022DOI:https://doi.org/10.1103/PhysRevAccelBeams.26.012801Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMethods in electromagnetismRadio frequency calculationsAccelerators & Beams

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.

Current distribution monitoring enables quench and damage detection in superconducting fusion magnets

Fusion magnets made from high temperature superconducting ReBCO CORC® cables are typically protected with quench detection systems that use voltage or temperature measurements to trigger current extraction processes. Although small coils with low inductances have been demonstrated, magnet protection remains a challenge and magnets are typically operated with little knowledge of the intrinsic performance parameters. We propose a protection framework based on current distribution monitoring in fusion cables with limited inter-cable current sharing. By employing inverse Biot-Savart techniques to distributed Hall probe arrays around CORC® Cable-In-Conduit-Conductor (CICC) terminations, individual cable currents are recreated and used to extract the parameters of a predictive model. These parameters are shown to be of value for detecting conductor damage and defining safe magnet operating limits. The trained model is then used to predict cable current distributions in real-time, and departures between predictions and inverse Biot-Savart recreated current distributions are used to generate quench triggers. The methodology shows promise for quality control, operational planning and real-time quench detection in bundled CORC® cables for compact fusion reactors.

Quench detection and early warning based on thermoelastic strain rate for HTS tapes thermally triggered by heat spots

The rapid detection and comprehensive monitoring of quench onset and evolution in high-temperature superconducting (HTS) materials remains immensely challenging because the normal zone propagation velocity in HTS materials is two or three orders of magnitude less than that in low-temperature superconductors. In this study, we experimentally and numerically explore quench events triggered by heat spots in yttrium barium copper oxide HTS tapes to characterize the quench onset and propagation. A multiplexed fiber Bragg grating sensor with multiple gratings was used to perform highly accurate strain measurements. Conventional voltage and temperature measurements were performed synchronously on the HTS tapes. A systematic comparison of these multifield signals during quench onset and development illustrated that the evolution of thermoelastic strain and strain-rate in HTS tapes captures the quench onset and propagation. A distinct feature was exhibited during the quenching of a pre-tensioned HTS tape: the thermoelastic strain initially relaxed but subsequently increased until the strain rate exhibited a significant slope change, which corresponded to the quench onset time. The thermoelastic strain in a nearly unconstrained HTS tape gradually increased until quenching occurred. A prominent characteristic for detecting quench onset in HTS materials have been revealed based on the change in the slope of the thermoelastic strain-rate or the second derivative of the strain remaining nearly constant. For a pre-tensioned HTS tape, the minimization of the thermoelastic strain or the strain-rate becoming zero may be a predictor that preceded the quench by ∼1–2 s, which can be, to a certain extent, regarded as an early warning. Another important and novel result was the experimental demonstration of global strain responses distant from the quench location in the pre-tensioned HTS tape, while the temperature and voltage detection are commonly localized methods. The mechanism behind these thermoelastic strain characteristics was further discussed and simulated from the induced Joule heating throughout the quench event. The measurements and numerical predictions suggested a new paradigm of quench detection based on the thermoelastic strain-rate in HTS materials.

Quench Detection for the Primary Windings of a 100-kA Superconducting Electric Transformer in the Conductor Performance Test Platform of the CRAFT

A superconducting electric transformer (SET) is a key element in the conductor performance test platform of the Comprehensive Research Facility for Fusion Technology, which has the capacity to provide around 100-kA test current for superconductor testing. Quench detectors based on voltage measurement is the considered solution for the quench detection in the primary windings (PWs) of the SET. One of the major problems to be encountered during the operation of the primary magnet systems is the expected inductive, coupled signals due to the current ramp up/down. For this case, Wheatstone bridge compensation can work. Regarding the hotspot temperature restriction, the quench detection threshold value and the holding time are given based on quench simulation results. Because the inductance of the PW is huge, the choice of dumping resistance plays a key role to ensure that the stored energy should be released safely if quench events occurred.

Time–Frequency-Based Quench Detection for HTS VIPER Cable Using Torsional Acoustic Wave

A new quench detection and diagnostic system is required for the reliable operation of high-field superconducting magnets for fusion which is fabricated with high-temperature superconductor (HTS) cables. The conventional voltage-based diagnostic methods have a limitation in detecting local temperature changes in large-scale HTS magnets. To address the limitation, an acoustic-based diagnostic method using torsional waves applied by piezoelectric transducers is proposed. In addition, from the sensor data collected by the piezoelectric transducers, a new monitoring index that can measure the temperature change is extracted via chirplet transform (CT), which is one of the time–frequency analyses. The proposed quench detection method using torsional wave guiding is implemented in a vacuum pressure-impregnated, insulated, partial dislocation, extruded, and roll-formed (VIPER) cable, and the performance of the new index, time–frequency-based phase delay, is validated. This work proves that the propagation characteristics of torsional acoustic waves depend on the strength and location of the heat and that the change can be monitored via the proposed time–frequency-based phase delay. The preliminary development and results of a new quench detection method are discussed to validate future use in complex environments such as fusion power plants.

Fabrication technology and performance tests for optical fiber-encapsulated, high-temperature superconducting tapes

Realizing fast and accurate quench detection is a great challenge for the application of long high-temperature superconducting (HTS) conductors. The combination of a distributed temperature sensing (DTS) system and optical fiber-encapsulated HTS (OFE-HTS) tape may become a promising approach to solve this problem. As a recently proposed composite HTS tape, its properties have not been studied systematically yet. Therefore, in this study, the electromagnetic and thermal behaviors of the OFE-HTS and traditional HTS tapes are compared by finite element simulation technology. The simulation results predict that the embedded optical fibers will hardly change the original electric, magnetic and thermal characteristics of the HTS tapes. In addition, a detailed fabrication method for OFE-HTS tape is introduced, and the composite tape performances including structural integrity, critical current uniformity, anti-bending/tensile force and quench response are tested seriatim. According to the microscope and x-ray detection results, the optical fibers are fully embedded in the OFE-HTS tape through the presented fabrication process. The critical current uniformity test results show the average critical current of the prepared 76 m long OFE-HTS tape is about 520 A, and the uniformity variation is about ±4%. The prepared OFE-HTS and traditional tapes have similar anti-bending/tensile properties. Finally, to check the effectiveness of the embedded optical fiber for quench detection, the fabricated OFE-HTS coil is tested. The quench detection results show that the temperatures in the same area measured by the optimized DTS system and a thermocouple are similar. Moreover, the temperature response ability of the optimized DTS system is better than that of the thermocouples, and the optimized DTS system is able to effectively avoid environmental electromagnetic field interference.

A Quench Detection and Monitoring System for Superconducting Magnets at Fermilab

A quench detection system was developed for protecting and monitoring the superconducting (SC) solenoids for the Muon-to-Electron Conversion Experiment (Mu2e) at Fermilab. The quench system was designed for a high level of dependability and long-term continuous operation. It is based on three tiers: Tier-1, FPGA-based Digital Quench Detection (DQD); Tier-2, Analog Quench Detection (AQD); and Tier-3, the quench controls and data management system. The Tier-1 and Tier-2 systems are completely independent and fully redundant. The Tier-3 system is based on National Instruments (NI) cRIO and provides the user interface for quench controls and data management. It is independent from Tiers 1 & 2. The DQD provides both quench detection and quench characterization (monitoring) capability. Both DQD and AQD have built-in high voltage isolation and user programmable gains and attenuations. The DQD and AQD also includes user configured current dependent thresholding and validation times. A 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> article of the three-tier system was fully implemented on the new Fermilab magnet test stand for the HL-LHC Accelerator Upgrade Project (AUP). It successfully provided quench protection and monitoring (QPM) for a cold superconducting bus test in November 2020. The Mu2e quench detection design has since been implemented for production testing of the AUP magnets. A detailed description of the system along with results from the AUP superconducting bus test will be presented.

Ultrasonic Waveguides for Quench Detection in HTS Magnets

High-temperature superconductors (HTS) are expected to have a major impact on the development of future particle accelerators and fusion energy systems. One of key challenges associated with HTS is a slow propagation of the normal zone that complicates early detection of thermal runaway (quench) in an HTS magnet using voltage-based techniques. Furthermore, fusion systems require field ramping rates up to several T/s under strong time-varying ac magnetic fields imposed on the conductor which makes voltage-based quench detection difficult or impractical. We propose an alternative non-voltage quench detection solution based upon monitoring ultrasonic wave propagation in a solid fiber-like flexible waveguide. The latter can be co-wound with the superconducting cable and carry acoustic waves over long distances. Acoustic waveguides allow for measuring local variation of strain or temperature in a way similar to optical fibers. However, unlike fiber-optic sensors, mechanical waveguides are constructed of robust materials and eliminate the need for expensive and complex signal receivers and data processing equipment. We will present our early developments in cryogenic ultrasonic waveguide technology, and discuss preliminary experiments conducted towards validating it for future use in practical HTS magnets.

Fast Quench Detection in SFCL Pancake Using Optical Fibre Sensing and Machine Learning

A fast hotspot detection technique has been implemented and patented at École Polytechnique Fédérale de Lausanne (EPFL) under the European Union project FastGrid. The optical fibre sensing based technique uses the Mach-Zehnder Interferometer (MZI) and can detect even singular hotspots in the superconductor within 15ms. The MZI setup is very sensitive to external perturbations and mechanical stresses, which can manifest in the output along with the response to hotspots. The disturbance the setup is subject to, varies with the sample being tested and the environment it is being tested in. For example, the sample length and configuration, in addition to the routing of the optical fibre can determine the extent of the stresses on the optical fibre. Previous publications, showcased experiment results on relatively simple sample configurations which were straight HTS tapes with short lengths (0.3m or 1m). This manuscript will investigate the technique feasibility for a more complicated sample type: a pancake prototype for a superconducting fault current limiter (SFCL), comprising 12m of HTS tape in a bifilar winding, with taped optical fibre along the length of the conductor. The manuscript will also give a brief overview of a machine learning based post processing technique for the experimental data, developed at EPFL to supplement the MZI based quench detection for easy and reliable quench detection in large scale applications.

Review on thermal-related measurement methods for superconducting devices and prospect for high-speed maglev transportation application

High-temperature superconducting (HTS) bulks can not only be self-stable when levitated above a permanent magnet (PM) but also can be used as quasi PM with higher magnetic energy product due to their magnetic flux pinning characteristics. Therefore, HTS bulks have wide application potentials in maglev trains, maglev bearings, flywheel energy storage, drug delivery, and high field magnets. In the external magnetic field of common application scenarios, HTS bulks have no external input current, so it is difficult to achieve the overall quench. However, local quenching in the bulk is still possible in the harsh fluctuating external field environment. Although it is difficult to reach the total quench, its critical parameters like Jc will inevitably deteriorate, which may collapse the application system. Therefore, in contrast to superconducting wires and tapes that are more concerned with quench detection, HTS bulks with a 3D volume effect are more focused on internal sensitive temperature locations, the impacts of volume and scale, and the coupling influence on application parameters such as magnetism and force. Therefore, for efficient thermal-related measurement of HTS bulk applications, this paper investigates and discusses 12 commonly-used temperature measurement or quench detection methods in all superconducting application fields. These methods primarily refer to the current quench detection technologies used in HTS tapes and wires. From the standpoint of practical temperature measurement requirements of HTS bulks and technological limitations of maglev application scenarios, working characteristics and service conditions of the 12 methods, and 4 temperature detection methods are selected through a comprehensive understanding and comparison of basic principles. They are expected to be used in real-time monitoring and early warning schemes for onboard superconducting levitation devices of HTS maglev transportation or other applications in the future.

Primary Quench Detection Analysis for DTT Central Solenoid and Poloidal Field Coils

The Central Solenoid (CS) and the Poloidal Field (PF) coils of the DTT tokamak (Divertor Tokamak Test facility, currently being built in the site of ENEA C.R. Frascati &#x2013; Italy) are operated in dynamic mode and, even in normal operation, the self and mutual voltages induced across each coil are of the order of magnitude of &approx;100 V. In DTT, these coils will be realized with superconducting materials and, as a consequence, a reliable and fast quench detection system is required in order to protect the magnets. Being the quench signals 4 orders of magnitude smaller than the operating voltages, the cowound (CW) technology must be adopted for the quench sensors, the only degree of freedom being among a wiring configuration merely aligned with the coil winding (CWA) or aligned and twisted to the coil winding (CWA&amp;TW). In this study, a model of the DTT poloidal magnetic system has been developed up to the details of the single windings (layer or pancake) of the various coils. CWA sensors have also been implemented in the model. Signals coming from the magnetic system and the CWA sensors during the Single Null plasma event have been simulated and compared. The analysis has been carried out up to the level of the elementary winding of each coil, using a lumped parameters circuital model. Finally, a simple theory has been developed aimed at the estimations of the improvements coming from the CWA&amp;TW architecture.

Quench Study on a REBa2Cu3Oy Coil for a High Temperature Superconducting Sextupole Magnet

We are developing a high temperature superconducting (HTS) sextupole magnet for the chromaticity correction of the electron and positron beams of SuperKEKB accelerator. The HTS sextupole magnet consists of six two-layers rectangular REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO) coils. Since quench protection is a critical issue for the HTS sextupole magnet, we have carried out a series of quench studies on the REBCO coil. As the same time, we have developed a numerical simulation code to perform quench protection designs for the HTS sextupole magnet. In this study, we performed experiments and numerical simulations on the quench characteristics of a two-layers rectangular epoxy-impregnated REBCO coil that is the same size coil for the actual HTS sextupole magnet. The hotspot temperature was studied as a function of the transport current and quench detection threshold. As a result, we experimentally confirmed that the quench protection of the REBCO coil could be achieved by a conventional quench detection method using the balance voltage. The validity of the numerical simulation was also confirmed by comparing with the experiments. Using the relation of the hotspot temperature and quench detection threshold, we could performed a protection design to limit the maximum quench temperature of the HTS sextupole magnet below 150 K.

Application of the Universal Quench Detection System to the Protection of the High-Luminosity LHC Magnets at CERN

The Universal Quench Detection System (UQDS) has been primarily developed to detect quenches in various superconducting magnets of LHC’s High Luminosity upgrade (HL-LHC). The functionality of the system, which comprises insulated high-resolution digitizing front-end channels and a central processing element, is mainly defined by the configuration of the central FPGA (Field Programmable Gate Array). Additional elements such as redundant power supplies, configurable interlocking capabilities and a communications controller are completing the functionality of the system. The system’s architecture is designed to be flexible enough to detect quenches in all superconducting elements of HL-LHC. The application-specific digital signal processing and quench detection algorithms are implemented in the firmware of the FPGA and thus can be changed according to the required specifications. To facilitate this process, the firmware has been structured accordingly and automated code generation techniques are used. The strategy of testing prototypes of the quench detection system with prototypes of the magnets allows an early evaluation of the system, minimizing operational issues in the final installation. This strategy has been already applied at CERN to the 11 T dipole magnets in previous years and extended as well to other magnet families of the HL-LHC Project. We give a system description and focus on the specific configurations for three different magnet families. Prototypes of these magnets have been recently tested at CERN. For each of these, specific features and detection methods have been developed, implemented and evaluated during the magnet tests.

Detecting Quench in HTS Magnets With LTS Wires—A Theoretical and Numerical Analysis

Protecting a high temperature superconducting (HTS) magnet from a quench event is a challenging task. Because of the slow normal zone propagation velocity, the long reliable quench detection method by directly monitoring coil voltage may not be timely for HTS anymore, leaving HTS magnets under danger of overheating. Using a NbTi low temperature superconducting (LTS) wire to detect quench in coils wound with ReBCO HTS tapes have recently been experimentally proved, yet a theoretical study is still needed to further develop this technique and make it prepared to be applied more generally in high field magnets. In this manuscript, we have demonstrated that it is the significant difference in the temperature dependence of critical current between LTS and HTS but not the normal zone propagation velocity (NZPV), that makes LTSs good quench detectors. Simulations show that LTS quench detectors should have low matrix fraction or high matrix resistivity. At last, at field up to 15 T or 20 T, Nb3Sn is proven to be a good quench detector.

Design, Fabrication and Soundness Test of A Bi2223 Magnet Designed for Cooling by Liquid Hydrogen

The critical heat flux in liquid hydrogen is ten times higher than that in liquid helium and is approximately half of that in liquid nitrogen. Since the resistivity of pure metal such as copper or silver at 20 K is less than one-hundredth of that at 300 K, HTS magnets immersed in liquid hydrogen are expected to satisfy the fully cyostable condition or to be stable against high resistive heat generation enough for quench detection at a practical current density. In order to examine cryostability of HTS magnets in liquid hydrogen, a pool-cooled Bi2223 magnet with a 5 T magnetic field at 20 K has been designed, fabricated and tested in liquid nitrogen prior to excitation tests in liquid hydrogen. The magnet consists of six outer double pancake coils with the inner diameter of 0.20 m and four inner double pancake coils with the outer diameter of 0.16 m. The resistive voltage to initiate thermal runaway in the coil assembly in liquid nitrogen was higher than 1 V that is sufficient high for quench detection.

Quench Protection of the HL-LHC Hollow Electron Lens Superconducting Solenoid Magnets

The High-Luminosity LHC (HL-LHC) project is an upgrade of the Large Hadron Collider (LHC) and comprises the installation of two Hollow Electron Lens (HEL) systems, each acting on one beam on both sides of LHC Point 4. The systems aim for a controlled depletion of hadron beam tails and an enhanced hadron beam halo collimation. Each HEL unit contains 22 circuits made up of solenoid, saddle coils and canted cosine theta corrector magnets. The largest magnet is a 1.6 m long solenoid, with a 180 mm bore diameter and central field of 5 T at 300 A and 4.5 K. This contribution focuses on the powering and protection strategy of the solenoid magnet circuits. The circuits are protected by active quench detection and a timely switch-off of the power converter. For the circuit with the largest stored energy, a study is performed on the efficiency of an energy extraction system. The quench simulations performed using the STEAM-LEDET code are combined with uncertainty quantification methods available in the DAKOTA software. Quench simulation input parameters related to the superconducting wire, magnet, circuit, and detection have been parametrized and randomly varied to calculate statistics of key output parameters. These are compared to the allowed limits, namely 500 V maximum peak voltage-to-ground and 120 K maximum coil temperature.

Flex-PCB Quench Antenna Developments at FNAL

Flexible printed-circuit-board-based quench antenna arrays have been developed at FNAL since 2017. They proved to be low-noise, low-cost, sensitive, and non-invasive sensors for quench characterization in superconducting magnets, having the potential to extend even to quench detection. Starting with applications of small area sensors of this type, we have explored feasibility for operations at high pressure, and have invested in multi-channel quench antenna arrays covering the complete area of the innermost magnet layer of the conductor. We've also tested and optimized sensor geometry and relative orientations to increase sensitivity and spatial resolution. Beyond developments of warm and cold bore antennas, we've progressed to concepts which attach quench antennas to the conductor surfaces of accelerator magnets. Multiple programs and projects at FNAL and collaborating institutions benefited from this work already and our plans target further extensions of capabilities and applicability of these devices. In this paper we present the logic behind the development steps taken so far, status of our work and direction of near-term research on quench antennas at Fermilab.

Thermal Hydraulic Analysis of JT-60SA TFC02 Complementary Quench Tests in CTF

In the framework of JT-60SA tokamak commissioning (Japan, 2021), the 20 Toroidal Field Coils (TFC) were tested at the Cold Test Facility (CTF) at CEA-Saclay (France, 2018) and submitted to quench acceptance test (quench temperature up to 7.5 K at nominal current). Some complementary quench tests were performed on the spare coil TFC02, with different conditions, especially reduced current (at 75% and 50% of nominal current) and delayed quench detection (holding time of 0.5 s instead of 0.1 s). A numerical model was developed, with SuperMagnet (fortran, CryoSoft) coupling THEA (Thermohydraulic and electric 1-D physics of Cable In Conduit Conductor, CICC) and Flower (Thermohydraulic model of cryogenic network). The measurements are presented and compared to simulation results. The acceptance quench test of TFC02 depicted a maximal helium temperature of 27 K. During complementary quench tests, delayed quench detection induced higher helium temperature of 37 K. At 75% and 50% of nominal current, a so called “smooth” quench occurred. It is characterized by slow quench propagation and low resistive voltage which increase the quench propagation time required before triggering current discharge although it reduces the Joule energy dissipated by the coil.

Processing of the Quench Detection Signals for CS Model Coil of CFETR

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T&#x002F;s without quench. Although adequate operational margins have been taken into in the design to avoid the quenches, such events cannot be completely excluded in the life of the CSMC. In order to prevent quench from damaging the CSMC, the quench detection by voltage measurements plays an important role in the protection of the CSMC during commissioning and operation scenarios. To improve the accuracy and reliability of CSMC quench detection, an all-digital quench detection system based on FPGA has been designed for the processing of quench detection signals. This paper describes the design of the quench detection signal processing system, including the composition of quench detection units, the auxiliary compensation for further denoising, the discriminant of quench, and the safety interlock system.