Quench Protection System Research Articles

Design, Simulation and Test Results of Quench Protection System for a 13-T Twin-Aperture Superconducting Dipole Magnet

Design, Simulation and Test Results of Quench Protection System for a 13-T Twin-Aperture Superconducting Dipole Magnet

Investigation of normal zone propagation velocity in AgSn/Ag/Ba122 superconducting tapes using a conduction cooling test system

The investigation of the behavior of quench propagation in iron-based superconducting (IBS) tapes is important for their application in magnets and the design of quench protection systems. However, little research has been done in this area. In this work, a conduction cooling test system for IBS tapes and coils has been built, which has functions such as charging test, temperature and voltage data acquisition, pulse current heating, quench detection and protection. A series of experiments were performed on several 27 cm long IBS tapes to measure their normal zone propagation velocity (NZPV). The variation trends of NZPV with different operating temperatures, and with different ratios of operating current to critical current were systematically explored. In addition, monitoring all the voltages between different positions of an IBS tape, including two joints, has provided more detailed results and findings.

Research on electromagnetic shielding device for pulse inductor in CRAFT quench protection system

The quench protection system is the most important safety equipment of the Comprehensive Research Facility for Fusion Technology (CRAFT) project, which is used to protect asset security in the event of superconducting device quenching. Since the pulse inductor of the quench protection system works under extreme conditions, a strong induced magnetic field will be generated around the equipment, which will affect the normal operation of other electrical equipment in the inductor cabinet. Aiming at this situation, it is necessary to analyze the changing magnetic field of the inductor. This paper proposed a new shielding structure that can effectively reduce the magnetic induction around the inductor, and the effectiveness of the design was verified through simulation.

Thermal runaway criterion as a basis for the protection of high-temperature superconductor magnets

High-temperature superconductor (HTS) based high-field magnet systems are essential for particle accelerators and fusion energy applications. Quench protection of such magnets is difficult owing to a slow quench propagation velocity in HTS. While in conventional NbTi and Nb3Sn-based magnets, a normal zone expands typically quickly, and the stored energy is dissipated across a large volume of the windings, a normal zone in an HTS magnet propagates slowly and, thus, can heat up quickly to high temperatures destroying the conductor. At the same time, growing experimental evidence suggests that HTS conductors can operate in a stable dissipative flux flow regime for a substantial range of operational currents before entering an irreversible thermal runaway. Therefore, a new protection paradigm for HTS magnets has emerged, aiming to prevent quenching, using advanced diagnostics to detect the dissipative regime onset. In the present paper, we propose a simple criterion for the thermal runaway in HTS conductors and calculate allowable temperature margins within which an HTS magnet can be operated safely. Outside of those temperature margins, a common quench integral approach may be used to estimate the upper boundary of the time margin for activating the protection system. We verify the applicability of our approach by comparing the calculated runaway conditions for a Bi-2223 conductor with the experimentally measured values. The thermal and time margins can define the quench protection system’s requirements for implementing the quench-avoiding protection paradigm.

Design of the water-cooling structure for the 100 kA DC mechanical switch in the CRAFT quench protection system

The DC mechanical switch is connected in series with the superconducting magnet in the quench protection system. As the main switch that carries the magnet current for a long time, the temperature of its conductive unit, especially the contact part, inevitably increases significantly during operation. It is necessary to design a water-cooled structure to control the temperature rise. This article introduces the structural design of the conductive unit of the DC mechanical switch for the Comprehensive Research Facility for Fusion Technology quench protection system and uses a combination of theoretical calculation, thermal-electrical coupling simulation, and Fluent simulation to analyze the thermal stability characteristics at a current level of 100 kA. By comparing and studying the temperature rise characteristics of switches under different cooling paths, diameters of water-cooling pipe, and water flow rates, a design basis is provided for determining a 15 mm diameter “∏” shaped cooling water path structure for the mechanical switch. The DC mechanical switch water-cooled structure designed in this article is expected to effectively control the temperature rise level of the contact.

Research on the action characteristics and breaking control of 100 kA series double break DC vacuum circuit breaker for CRAFT quench protection system

The DC vacuum circuit breaker plays an important role in the quench protection system of the Comprehensive Research Facility for Fusion Technology (CRAFT) project. The study of the operating characteristics of vacuum circuit breakers can effectively improve breaking reliability. This article introduces the design and basis of the series double break DC vacuum circuit breaker for the CRAFT quench protection system. It adopts the electromagnetic repulsion driving method to ensure rapid action and the operating mechanism design to ensure the synchronization of the double break action. A magnetic shielding setting is proposed through simulation calculations to solve the uniformity of magnetic induction strength between breaks. Combining the test data of action characteristics with the theory of optimal opening distance for current zero crossing, a DC breaking platform for the vacuum circuit breaker was designed, and control strategies were determined, thus completing the 100 kA DC breaking experiment. The vacuum circuit breaker studied in this article meets the technical requirements of the CRAFT quench protection system and provides experience and experimental data for the design of high-current vacuum circuit breakers.

Design and Test of Magnetic Shielding for Vacuum Circuit Breaker of CRAFT Quench Protection System

Design and Test of Magnetic Shielding for Vacuum Circuit Breaker of CRAFT Quench Protection System

Design and Test of a Curved Canted–Cosine–Theta Superconducting Dipole Magnet for Next Generation Ion Therapy

The curved superconducting dipole magnet is the core component of the next generation ion therapy device. The superconducting dipole magnet prototype with a physical bend angle of 90°, a magnetic bend angle of 45°, a bend radius of 800 mm, and a bore of 98 mm diameter is developed in China based on a novel type of Canted–Cosine–Theta (CCT) coil structure. The magnet design and manufacturing, and the quench protection system are reported first, and then testing process of this curved CCT superconducting magnet, which reached the nominal current of 610 A and generated the magnetic field of 2.018 T after five quench trainings in liquid helium test is reported, meeting the design indicators. A set of technical routes is explored through the development of the curved CCT magnet, providing support for the future ion therapy.

Quench Protection by Putting a Current-pulse Into a Coil Center-Tap in HTS Coils

Forty years ago, Lawrence Berkeley Laboratory (LBL) tested a pulsed current quench protection system for a high current density two-meter diameter two-layer solenoid at 4.5 K with a stored energy of 8.5 MJ. The energy needed to protect this magnet was 13.4 kJ from an electrolytic capacitor system charged to voltages 800 V. This method also involved the use of a well-coupled shorted secondary circuits and quench-back. The applicability of this quench protection method to HTS magnets operating at temperatures >25 K could be of interest. There are a number of questions that should be asked: 1) Can this method work for HTS coils operating at temperatures >25 K? 2) Are there batteries or capacitors that can store 2 MJ or more that have short enough discharge times for quench protection at voltages less than 2 kV? 3) Is this quench protection system cost low enough to be reasonable?

Evaluation of Frequency Loss Induced Quench Protection Prototype at 77 K Using HTS Coils

A prototype design of the Frequency Loss Induced Quench (FLIQ) protection system for high temperature superconducting magnets was validated on a small Second-Generation High-Temperature Superconducting (2G HTS) coil. Calorimetric measurements, based on liquid nitrogen boil-off rate, were performed to quantify the heat energy introduced by FLIQ system in the coil. The technique was previously used for steady state AC loss measurements and adopted for the transient losses generated in FLIQ operation. A series of tests of the FLIQ system on 2G HTS pancake coils were performed to study the dynamics of the quench and the energies involved in the quenching process. The results suggest the suitability of the FLIQ technique for quench protection of HTS coils. A measurement protocol of extended repetitive high-frequency current pulses established in the study provided a way to estimate the energy deposited by the AC losses generated in the coil by the FLIQ system. The measurement method described is a practical way to validate the design parameters of the FLIQ system and to evaluate the sensitives of the various design parameters of the FLIQ. The paper reports an experimental technique used to study the sensitivities of various FLIQ design parameters by establishing and measuring quasi-equilibrium heat load and boil-off rate as a result of extended repetitive high-frequency current pulses.

External Coil Coupled Loss Induced Quench (E-CLIQ) System for the Protection of LTS Magnets

The next generation of Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn accelerator magnets are pushed to higher magnetic fields, higher stored energy and higher energy density. This brings additional challenges when it comes to quench protection. At CERN, a fast quench protection system is under development that introduces normal zones directly in the coil's conductor by inductive heating. This system is called External coil Coupled Loss Induced Quench (E-CLIQ). The E-CLIQ device comprises many small copper coils that are strategically placed near the main coils. Once a quench is detected, a capacitor is discharged in to the E-CLIQ coils, resulting in the characteristic damped oscillating current of an RLC circuit. This results in a large, but local applied dB/dt on the conductor of the main magnet system, which locally heats it by induced interfilament and interstrand coupling loss. Such a system has the advantage of being fast by introducing normal zones in potentially less than 10 ms, it doesn't rely on heat flow through the insulation layers of the coil, as is the case with traditional quench heaters, and it is not electrically connected to the main circuit. In this paper, the E-CLIQ system is introduced, several first demonstrator coils are presented and the results of a first proof-of-concept test are shown.

Stability Analysis of 14-T-Level High-Performance Nb3Sn Cable-in-Conduit Conductor for a Toroidal Field Coil

In view of the fact that the fusion power of fusion reactor is proportional to the fourth power of the toroidal magnetic field, the design of toroidal field (TF) magnetic system is particularly important for achieving higher operating parameters. In order to meet the confinement requirements of high plasma parameters, the high field region of the TF magnetic system can be wound by high-performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cable-in-conduit conductor (CICC), with a maximum magnetic field reaching 14.32 T. Since the stable operation of the TF magnetic system relies heavily on the stability of the superconductor, a stability analysis of high-performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn CICC conductor has been performed. The results indicate that the current sharing temperature of the conductor is 6.9 K under extreme working conditions ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> = 14.32 T), which meets the design requirements; the minimum quench energy (MQE) is 116 mJ/cc under short perturbation, but under long perturbation it is only 20.3 mJ/cc. Therefore, several options may be available to increase the MQE of the conductor, such as reducing the strain, operating current and thermal resistance, or increasing the helium mass flow rate. In addition, the quench behavior of the CICC conductor is also evaluated. Studies have shown that increasing the area of copper and decreasing the thermal resistance and quench detection threshold voltage can lower the hot spot temperature. These analyses provide references for the design of 14-T-level high-performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn CICC conductor and its quench protection system.

Advances in Searching for Galactic Axions with a Dielectric Haloscope (MADMAX)

AbstractAxions are hypothetical particles that could explain the observed dark matter density and, simultaneously, could naturally resolve the strong charge parity (CP) problem in quantum chromodynamics (QCD). Recent theoretical works indicate that axions are expected to have masses in the range of , a range that presently still evades experimental detection. An experimental design is presented to search for QCD axions in this mass range via the magnetized disk and mirror axion experiment (MADMAX). MADMAX will be composed of multiple movable dielectric disks and a stable mirror that are placed inside a strong magnetic field to utilize the axion‐induced coherent electromagnetic wave emissions from each disk surface. In this paper, new R&amp;D milestones achieved will be reported, that is, the updated magnet quench protection system, a closed booster dielectric haloscope system tested in the MORPURGO magnet at (European Organization for Nuclear Research) CERN using a full experimental data acquisition chain. These new main novel accomplishments investigate the feasibility of the experiment.

Measurement of zero-zone voltage for vacuum circuit breaker with oscillation zero-crossing circuit

Vacuum Circuit Breaker (VCB) with oscillation zero-crossing circuit is wildly used to interrupt high direct current, especially in the magnet quench protection system. The injection time of reverse current is the critical factor that affect the breaking result. During the current breaking period, the voltage of VCB varies in a wide range, while the arc voltage in zero-zone is very small and changes rapidly. Therefore, the conventional methods cannot meet the voltage measurement requirements. In this paper, a bi-directional zero-zone voltage measurement scheme for VCB was proposed. According to the variation characteristics of transient voltage during the breaking process, the design and simulation verification of the measurement device were completed. Then the high voltage impulse experiment and arcing measurement testing were carried out by the developed prototype of the arc voltage measurement device. The experimental results indicated that the device has fast response and high measurement accuracy, which meets the measurement requirements of VCB zero-zone voltage.

100 kA/10 kV thyristor stack design for the quench protection system in CRAFT

Thyristors have longer lifetimes, higher reliability, and very high voltage and current ratings and they require less maintenance than other high-power semiconductor devices. As a result, they are particularly suitable for quench protection systems (QPSs), which protect the superconducting magnets in large fusion devices from damage. In this paper, we propose a design for a 100 kA/10 kV thyristor stack supported by both theoretical and simulation-based analyses as well as experimental verification. Due to the ultrahigh electrical performance requirements imposed on the QPS by the Comprehensive Research Facility for Fusion Technology (CRAFT), three main issues must be considered: the voltage-balancing problem caused by multiple thyristors in a series structure, the increased junction temperature problem caused by extremely high currents, and the reverse recovery phenomenon that arises from the thyristor’s physical structure. Hence, a series of detailed theoretical analyses, simulations, and experiments, including a thyristor junction temperature prediction method and reverse recovery process modeling, were carried out to optimize the design. Finally, the reliability and stability of the thyristor stack were verified by a series of prototype experiments. The results confirmed the correctness and accuracy of the proposed thyristor stack design method and also indicated that the proposed thyristor stack can meet the application conditions of a 100 kA QPS in the CRAFT project.

Research on Dynamic Voltage Balancing of Series Connected Thyristors in Auxiliary Oscillation Zero-Crossing Circuit

As a mature power semiconductor, the thyristor is widely used in high-power electrical systems. However, its performance and type selection are still worth discussing in some unconventional applications. In this article, the dynamic voltage balancing the performance of series connected thyristors in an auxiliary oscillation zero-crossing circuit designed for a 10 kV/100 kA Quench Protection System (QPS) is discussed. This pulse power circuit contains a bidirectional switch composed of four thyristor stacks, which are used to inject reverse current into the parallel vacuum circuit breaker (VCB) to interrupt the dc circuit. It is proven by both analysis and experiment results that although there is a high di/dt conduction requirement, the ordinary power thyristors are proof that it is more suitable than pulse power thyristors on this occasion for their better transient reverse recovery voltage balancing performance. The phenomenon is explanted by physical principles and measurement results.

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.

The conceptual design of upgraded 100 kA quench protection system for CRAFT superconducting magnet

In the previous scheme of 100 kA Quench Protection System (QPS) in Comprehensive Research Facility for Fusion Technology (CRAFT) project, advanced artificial current zero-crossing technology was used to interrupt the current. Also, the feasibility was verified by both simulation and experiment. However, some significant issues were exposed, including the breaking reliability problems caused by randomness of the post arc and uneven distribution of the recovery voltage in vacuum circuit breaker. In view of the problems, it is of great significance to upgrade the QPS design scheme in CRAFT project. In this paper, a new 100 kA/10 kV QPS topology is proposed, and the working principle of the new topology is introduced firstly. Then the complete commutation process is divided into three stages to carry out a more effective analysis of the theoretical feasibility of the new topology. Furthermore, a series of simulations including the electrical performance of each device in commutation process and temperature prediction simulation of the used semiconductors are carried out. Finally, the optimized design scheme is obtained to meet the technical requirement of CRAFT project. Compared with the previous QPS scheme, the new scheme has much higher action speed and lower cost.

Analysis of the Thermal-Hydraulic Effects of a Plasma Disruption on the DTT TF Magnets

The Divertor Tokamak Test (DTT) facility, a fully superconducting nuclear fusion reactor being built in Italy, will contribute to address the power exhaust problem in EU DEMO perspective. A lot of flexibility of operation will be demanded to the machine, which should be capable to tackle also severe transients such as plasma disruptions. In this work, the 4C thermal-hydraulic code is used to compute the temperature margin during a plasma disruption, using as input the heat generated into the Toroidal Field coil casing and transferred to the winding pack, and the possibility that this leads to a quench of the magnet is studied. The results of the analysis will give important feedbacks for the design of the quench protection system, e.g., avoiding to trigger a fast current discharge right after the disruption, as well as for the machine operation, e.g., assessing the required re-cooling time of the magnets after a disruption.

The Effect of Different Copper Discs on the Discharge of Superconducting Coils

High temperature superconducting (HTS) magnets often work at high energy density and have slow quench propagation speed, so a quench will present a serious risk to the safety of magnets. The quench protection method based on the dump resistance can effectively reduce the current and release the energy in the HTS magnets. However, too large dump resistance may cause excessive voltage across the magnets. A quench protection system consisting of dump resistances and metal discs has been proposed. Copper discs are often embedded in HTS magnets for conducting cooling and mechanical support. In the discharging process of HTS magnets, the copper discs can absorb energy from the magnets through magnetic coupling, thus accelerating the current decay of the magnets. This quench protection method is more effective than using dump resistance alone. In this paper, the effect of different copper discs on the discharging process of HTS coils is discussed. Eight types of copper with different residual resistivity ratios (RRR) are applied. The results show that with the increase of the RRR of the copper disc, the current decay rate of the coil increases, and the energy absorbed by the copper disc from the coil increases. The role of different copper discs in the fast quench protection of the coil can be sorted as: RRR = 300 &gt; RRR = 100 &gt; RRR = 80 &gt; RRR = 60 &gt; RRR = 40 &gt; RRR = 30 &gt; RRR = 20 &gt; RRR = 10. The copper disc with RRR of 300 shows the best performance in quench protection of HTS coils.