Quench Protection System Research Articles

Characterization of the Copper Resistance in the LHC Main Dipole Bypass Diode Leads

A fundamental component of the quench protection system of the large hadron collider (LHC) superconducting dipole magnets are bypass diodes. During a quench, the high current powering the magnet coil is redirected through the parallel diode. The resistance of diode current lead contacts is essential due to the risk of overheat. There is no possibility to measure their resistances, as the superconducting magnet coil acts as a short-circuit. Those measurements are possible when the magnet is in the resistive state. The most important point is the contact surface between the magnet busbar and the diode current lead. The resistance of this contact is not possible to measure when the cryostat is closed, so an indirect method that includes the resistance of the copper parts has to be developed. This article describes the methodology of measurements and calculations and summarizes the results of the resistance measurements of copper current leads of the LHC dipole bypass diodes. The measurements have been performed in a wide temperature region, to reproduce different environmental parameters of the LHC. It was proven that the temperature of measured samples has a significant influence on obtained results and a systematic approach is essential. Precise values of the resistance parameters have been obtained and will be used in the future measurements of the quality of connection of those diodes and, in consequence, will be used in the quality assurance of the quench protection system.

Numerical Study on Multiple Arcs in a Pyro-Breaker Based on the Black-Box Arc Model

The arc behavior during commutation of a pyro-breaker is the main determinant of performance evaluation. The pyro-breaker discussed in this article is an explosive-driven, extremely fast and non-linear Direct Current circuit breaker. It has been developed for the Quench Protection System (QPS) of superconducting fusion facilities, such as the China Fusion Engineering Test Reactor (CFETR). The feasibility of the Schavemaker differential equation is verified in a simplified 40 kA commutation simulation. The Commutation Section of the pyro-breaker will form multiple gaps after the operation, which causes multiple arc ignitions during the explosion. The influence of the gap quantity on the commutation performance of the pyro-breaker has not previously been studied. A more accurate simulation, which takes the multiple-arc formation into consideration, is proposed and verified under the current of 60 kA. The simulation model, which takes the numerical analysis of the driving mechanism into consideration, will be the designing basis for the pyro-breaker in further development and implementation.

Low cost, simpler HTS cable conductors for fusion energy systems

The cost and complexity of large, high-field superconducting magnet modules and related subsystems comprise 30% to 60% of the fusion reactor core capital cost. The strategic plan for the U.S. burning plasma research, the Fusion Energy Sciences Committee Report (FESAC) “Power the Future: Fusion and Plasmas’', and 2021 NASEM report “Key Goals and Innovations needed for a U.S. Fusion Pilot Plant” recommends that the U.S. pursue innovative science and technology to enable construction of a Fusion Pilot Plant (FPP) that produces net electricity from fusion at reduced capital cost. To achieve this, a novel combination of lower-cost high temperature superconductors (HTS) in cable configurations with co-wound reinforcement for higher current density are being investigated using a simplified construction strategy to produce compact stable coils. They would be capable of generating 20 T at up to 10-20 K. Small-scale, inexpensive test coils and prototypes will help develop each feature and validate cabled conductor design models. The near term goal is to validate engineering approaches, scientific models and fabrication capabilities applicable to fusion reactor development such as U.S. fusion nuclear science facility (FNSF), sustained high-power density tokamak facility (SHPD) and FPP designs. The design options include lower-cost, high-strength, quench resistant REBCO or Bi-2212 cables in an all metal coil design that simplifies HTS coil construction and quench protection system, with co-wound reinforcements that integrate stress management in HTS cable design and provides thermal mass to help prevent quench damage.

The challenge and solution of overvoltage for 100 kA Quench Protection System in CRAFT project

The high parameters of superconducting magnet in Comprehensive Research Facility for Fusion Technology (CRAFT) project can reach 10 kV/100 kA, which pose great challenge to the design of Quench Protection System (QPS). In particular, the large-scale discharge resistor built for consuming electromagnetic energy stored in superconducting coils, will bring unneglected stray inductance to operating circuit. Therefore, a transient overvoltage may be generated to fail the breaking process and damage the magnet insulation. In this paper, the generation and effects of overvoltage are discussed in detail and verified by simulation. This paper proposes an optimal snubber circuit to constrain overvoltage. By analyzing the commutation process of QPS with snubber circuit, the electrical equations and value selection principles are determined. In addition, the overvoltage constraint effects under different parameters of snubber circuit are compared by simulation. Finally, a set of optimum parameters is proposed to meet the requirements of voltage constraint and cost control.

Analysis and redesign of the thermal shield for the 40-T hybrid magnet at the CHMFL

A 40 T hybrid magnet has been constructed and commissioned at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL). It consists of a 10 T superconducting outsert magnet and a 30 T resistive insert magnet. As an important component of the hybrid magnet, the 80 K thermal shield is located inside of the cryostat protecting the superconducting magnet from thermal radiation. During the commissioning phase, a trip of the water-cooled resistive magnet triggered the quench protection system of the superconducting magnet, huge induced currents resulting in expansion and rupture of the oxygen-free copper thermal shield. In this paper, the cause of thermal shield rupture was investigated via finite element simulations. And the structure design and mechanical assessment of a new alternative thermal shield adopted for the 40 T hybrid magnet is presented.

Quench position reconstruction through harmonic field analysis in superconducting magnets

The performances of superconducting magnets for particle accelerators are limited by instabilities or disturbances which lead to the transition of the superconducting material to the normal resistive state and the activation of the quench protection system to prevent damage to the magnet. To locate the position of the state transition, voltage taps or quench antennas are the most commonly used technologies for their reliability and accuracy. However, during the production phase of a magnet, the number of voltage taps is commonly reduced to simplify the construction process and quench antennas are generally used only for dipoles or quadrupoles to limit the antenna design complexity. To increase the accuracy in the reconstruction of the quench event position, a novel method, suitable for magnets with independent superconducting coils and quench protected without the use of quench heaters, is proposed in this paper. This method, based on standard magnetic measurement techniques for field harmonic analysis, can locate the position of the superconductor transition inside the magnet after the quench event when the magnet has been discharged. Analyzing the not allowed harmonics produced in the field quality at zero current, the position of the quenched coils can be retrieved for any magnet orders without increasing the complexity of the dedicated measurement technique.

Numerical Analysis of the Convective Heat Transfer Coefficient Enhancement of a Pyro-Breaker Utilized in Superconducting Fusion Facilities

The conductive components of the pyro-breaker in the quench protection system (QPS) have high current density, a large number of electrical contacts and high thermal flux. The water system needs to meet the requirements of cooling and arc extinguishing at the same time. In a previous study, the bottleneck of the steady-state capacity appeared in the barrel conductor of the commutation section, which has a cylindrical cavity. The thermal stability of the commutation section at 100 kA level was simulated in ANSYS/Workbench. The results indicate a certain level of enhancement of the convective heat transfer coefficient of the cavity is required to reach the current capacity. However, the fluid flow inside the cavity is very complex, and the convective heat transfer coefficient is difficult to calculate. In this paper, Computational fluid dynamics (CFD) is applied to the optimization of the cooling water system of the pyro-breaker. By studying the enhancement method of convective heat transfer, optimization of the structure and processing method of the water channel are proposed. The convective heat transfer coefficients of the cylindrical cavity in these optimizations were calculated in CFX. A set of optimizations of the cavity, which can meet the requirements of China Fusion Engineering Test Reactor (CFETR), were obtained and verified by experiments.

Quench Protection System of a Whole-Body Non-impregnated 1.5 T Superconducting MRI Magnet

A quench protection system for an actively-shielded whole-body 1.5 T MRI magnet made with wire-in-channel NbTi conductor is presented with two types of coil sub-divisions. The MRI magnet must operate for many years in the hospital, and thereby, it must be completely self-protecting by means of self-activating quench propagation heaters to spread the normal zone in a larger volume of the magnet during a quench i.e. the passive protection system. The total stored energy of the magnet is about 3.7 MJ. The voltage and the temperature of the coils have been simulated with two types of passive quench protection systems using OPERA-Quench program. The maximum inter-layer quench voltage generated in the asymmetric sub-division is 70 V/layer with a peak voltage of 2.6 kV and a hot spot temperature of 248 K. The maximum inter-layer quench voltage generated in the symmetric sub-division is 45 V/layer with a peak voltage of 1.7 kV and a hot spot temperature of 185 K. During a quench, an average driving voltage of 1.3 kV and the associated current of 1.75 A is generated in both quench propagation circuits of the magnet with the symmetric sub-division. The 5 G safety line explodes beyond the permissible limits during a quench of the magnet with the asymmetric sub-division, whereas the 5 G safety region is retained within the permissible limit in case of quench of the magnet with symmetric sub-division.

Electrical Model of Frequency Loss Induced Quench Protection System for High Temperature Superconducting Magnets

Frequency Loss Induced Quench (FLIQ) is an active protection system designed to generate heat from AC losses to uniformly and safely quench a superconducting coil. It drives an imbalance in the transport current between two or more sections of the magnet using the H-bridge design with Insulated Gate Bipolar Transistor (IGBT)s, whose gates are controlled based on the current feedback within its loop. This allows FLIQ to operate at resonance with the frequency of the load. The performance of FLIQ circuit was characterized using simulations to assess the relative effectiveness of the key parameters of voltage, frequency, and time. The results show that the voltage is the most effective parameter. It was shown that with the selection of appropriate values of the parameters, the FLIQ system released sufficient energy into the coil to quench it.

Updates on fast discharge resistor system for comprehensive research facility for fusion technology

When quench happens, the energy stored in the superconducting magnet is required to be transferred and consumed to fast discharge resistor (FDR) system in specific time by quench protection system (QPS). In the previous research, the design made of 1 mm SUS304 has a bad cooling effect due to the narrow wind channel. So, the updated design concerning the cooling problem as well as the stray inductance is asked. The updated FDR system focuses on the basis of solving thermal and inductance proportional inverse problem. The scaled model machine is developed to testify the design rationality. With the update, the newly developed FDR system can provide less heat accumulation and accelerate up the cooling-down speed without bringing more stray inductance.

Application of an Improved Mayr-Type Arc Model in Pyro-Breakers Utilized in Superconducting Fusion Facilities

Pyro-breaker, a fast-responding, highly reliable and explosive-driven circuit breaker, is utilized in several Quench Protection Systems (QPS). The commutation process and its parameters are the main technical considerations in the process of designing a new pyro-breaker. The commutation parameters, such as the commutation time and the current change rate, are not only determined by the electrical parameters of the commutation circuit but also the arc behavior during the operation. The arc behavior is greatly affected by the structure and the driving mechanism of the Commutation Section (CS) in the pyro-breaker. The arc model was developed decades ago and the black-box arc model is considered a valid method to study arc behavior. In this paper, the Schavemaker black-box arc model, an improved Mayr-type arc model, is applied to study the commutation process of a newly designed pyro-breaker. Unlike normal circuit breakers, the arc discussed in this paper is discharged in deionized water. A parameter selection method is proposed. The practicability of the method is verified by numerical calculation in Power Systems Computer Aided Design (PSCAD) and experimentally.

A new structure of mechanical switch used for hybrid breaker in quench protection system

High power DC breaker is the most important device in the quench protection system of superconducting magnet. In this paper, a new structure mechanical switch with three levels contacts is presented, which is designed for high current hybrid breaker in quench protection system on China Fusion Engineering Test Reactor (CFETR). The topology and operation logic are discussed, and the prototype of hybrid breaker with 10 kA level has been tested. In addition, the corresponding simulation mode of breaker is built by MATLAB/Simulink. The prototype experimental and simulation analysis prove that the mechanical switch can interrupt the current more quickly and reduce the conducting time of solid-state switch.

Quench and Stability Modelling of a Metal-Insulation Multi-Double-Pancake High-Temperature-Superconducting Coil

The most detailed, first-principle simulation model of a quench in a high-temperature superconducting metal-insulation multi-module/multi-double-pancake coil, wound with a REBCO coated superconductor/tape and normal-metal tape (co-wind), was developed. It enables one to simulate a normal zone propagation, or non-propagation, in the subtle multi-turn structure of the coil's pancakes due to the inductive coupling and transverse electric contact between all the REBCO turns and co-wind turns along with the external circuit and active and passive quench protection systems. In doing so, the multi-module coil's structure is represented as a “rectilinear equivalent” electric circuit, a branched multi-decker multi-rectangle planar grid, which facilitates the mathematical formulation, using the standard electric circuit differential equations and the Kirchhoff's rules. The transient non-linear comprehensive heat conduction equations are employed to model the thermal part of the phenomenon at the same level of detail. All this turns the model into an effective design tool for metal-insulated, -stabilized and/or -reinforced multi-module coils. A parametric study of quench in a 6-module no-insulation (NI) test coil, using a stainless-steel thin co-wind, was conducted to identify the possibilities of the model. The profound effect of the transverse contact resistivity on an NI-coil quench behavior is confirmed and detailed.

Design and Construction of a High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory, together with Lawrence Berkeley National Laboratory, is building a new High Field Vertical Magnet Test Facility (HFVMTF) to be situated in the Magnet Test Facility at Fermilab. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics, and Fusion Energy Sciences, and will serve as a superconducting cable test facility for both communities. The background magnetic field for test samples is 15 T and will be produced by a magnet provided by LBNL operating at 1.9 K in superfluid helium. The samples will be placed in the background magnetic field, cooled to between 4.5 K and a user-specified upper limit, and will be powered with a superconducting transformer at up to 100 kA. Additionally, this facility will be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program. Currently, the various tasks of the project are at different stages of execution, from conceptual to ready-for-construction designs. This paper describes the parameters and design status of the pit construction, cryostat, heat exchanger, lambda plate, power system, and quench protection and monitoring systems of the facility.

The Quench Detection System Based on Programmable FPGA and Its Application at IMP

The High Intensity heavy ion Accelerator Facility (HIAF) and Low Energy heavy ion Accelerator Facility (LEAF) of IMP are under construction. They will comprise many superconducting devices and components, such as magnets and current leads, with the superconducting materials covering NbTi, Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and HTS. On the other hand, most of the superconducting devices have a high energy density and complex structure, requiring a targeted and active protection. In previous quench protection systems implemented at IMP, the quench detection was implemented in software or as microcontroller-based equipment, where power supplies in superconducting circuit provided quench detection functionality as well. These systems have some disadvantages, such as limited functionalities, poor reliability and high susceptibility to interference. Therefore, a new type of quench detection system (QDS) based on programmable FPGA and Isolated analogue input front-ends was developed to overcome these challenges. It is important to note that in the test facilities, there is no ionizing radiation, the QDS does not require radiation tolerance, thus a commercial programmable FPGA product was chosen as the development platform. The QDS is currently being put into operation, and some good results have been obtained in the cold tests of MCBRDP2 (belongs to HL-LHC, NbTi magnet) and FECR (belongs to LEAF, Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnet). Based on these successful applications, the new QDS has proven its functionality. The recorded data and practical experience also provided relevant information for the detection algorithms and functional upgrades.

Intelliquench: An Adaptive Machine Learning System for Detection of Superconducting Magnet Quenches

In superconducting magnets, the irreversible transition of a portion of the conductor to resistive state is called a “quench.” Having large stored energy, magnets can be damaged by quenches due to localized heating, high voltage, or large force transients. Unfortunately, current quench protection systems can only detect a quench after it happens, and mitigating risks in Low Temperature Superconducting (LTS) accelerator magnets often requires fast response (down to ms). Additionally, protection of High Temperature Superconducting (HTS) magnets is still suffering from prohibitively slow quench detection. In this study, we lay the groundwork for a quench prediction system using an auto-encoder fully-connected deep neural network. After dynamically trained with data features extracted from acoustic sensors around the magnet, the system detects anomalous events seconds before the quench in most of our data. While the exact nature of the events is under investigation, we show that the system can “forecast” a quench before it happens under magnet training conditions through a randomized experiment. This opens up the way of integrated data processing, potentially leading to faster and better diagnostics and detection of magnet quenches.

Quench Protection Studies for the High Luminosity LHC Nb$_3$Sn Quadrupole Magnets

Achieving the targets of the High Luminosity LHC project requires the installation of new inner triplet magnet circuits for the final focusing of the particle beams on each side of the two main interaction points. Each of the four circuits will include six 150 mm aperture, 132.2 T/m gradient, 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 quadrupole magnets to be installed in the LHC tunnel. The recently updated circuit topology is such that the protection of each magnet can be studied from a single magnet point-of-view. To limit the hot-spot temperature and the peak voltage-to-ground, a protection system was designed that quickly and reliably transfers voluminous parts of the coil to the normal-conducting state, hence distributing more homogeneously the magnets stored energy in the windings. This system is based on two elements: quench heaters attached to the outer layers of the magnet coils and CLIQ (Coupling-Loss Induced Quench). The performance of the protection system is investigated by simulating the electro-magnetic and thermal transients occurring after a quench with the program STEAM-LEDET, and by conducting dedicated experiments at the CERN and FNAL magnet test facilities. The effectiveness of the quench protection system is assessed at all representative operating current levels. Furthermore, the coils hot-spot temperature and peak voltage to ground are analyzed for various failure cases, conductor parameters, and parameter distribution among the four coils. It is concluded that the proposed design assures an effective, reliable, and fully redundant quench protection system.

Demonstration of engineering current density exceeding 1 kA mm−2 in ultra-thin no-insulation, soldered coil windings using NbTi/Cu wires with CuNi cladding

The no-insulation, or more precisely, controlled-resistance coil winding method, nowadays being exclusively used for high-temperature superconducting solenoids, has proven its effectiveness for improving quench protection. When considering low-temperature superconductor magnet technology, which is mostly focused on stability and training issues, controlled-resistance insulation windings are directly addressing these aspects as well. Fully soldered coil windings of non-insulated turns can also show superior mechanical properties and feature simplified manufacturing when compared to epoxy impregnated coil windings and are of high practical interest for quasi-stationary magnets provided the related charging time constant can be controlled and kept low enough. For demonstrating the principle feasibility two demonstrator coils were developed using NbTi/Cu wire with CuNi cladding of 1 mm diameter. The wire performance is reported including critical current and n-values at 4.2 K and background magnetic fields from 0 to 9 T, as well as effective transverse resistivity at room temperature and 77 K. Two solenoids with fully soldered windings comprising one layer on a 50 mm bore and three layers on a 100 mm bore, respectively, were manufactured and tested in liquid helium. Their performance is directly compared to data obtained on short wire samples. The drastically enhanced stability of the coils against thermal disturbances allows to avoid any training and enables to operate the coils up, or even slightly beyond, the short-sample critical current, resulting in generated magnetic fields of 2.2 and 3.8 T and time constants of 5 and 55 s, respectively. When initiating a quench deliberately by excessive heating or spontaneously at their limiting currents, the coils entirely switch to the normal state almost instantly, thus requiring no quench protection system. Design, manufacturing and test experiences with the two super stable coils are reported and their use and design constraints for certain applications discussed.

Development of the quench protection system for the CFETR CS model coil

The Central Solenoid (CS) model coil, which is responsible for developing and verifying the larger-scale superconducting magnet technology of China Fusion Engineering Test Reactor (CFETR), has been designed and is currently being manufactured at ASIPP. The energy storage of the CS model coil is 407MJ, so a reliable quench protection system is needed to ensure the safety of the coil when a quench occurs. This paper describes the progress of the quench protection system. The two-stage commutating current technique is used to solve the difficulties that the breaker cannot directly break the high DC current. For the key components in the circuit, the prototype of the breaker was manufactured and the performance test was carried out. The engineering design and manufacture of the discharge resistor were carried out. An experimental study of the quench protection circuit was carried out to verify the feasibility of the design. Besides, the reliability of the quench protection control system is qualitatively analyzed based on the fault tree.

Development of No-Insulation Racetrack Coils Wound With 2nd Generation HTS Tapes for a Stator System for Wind Generators

With the high current carrying capacity of second generation superconductors the increase of power density of electrical devices is a main research subject in the field of superconductors application. Especially, compact and more lightweight generators in offshore wind turbines would result in a reduction of the levelized cost of energy. To avoid the use of cryogenic liquids and reach temperatures below 77 K a conduction cooling method for keeping the coils at their operating temperature is envisaged. Furthermore, the possibility of an increased thermal and electrical stability of coils without a turn-to-turn insulation could make the need of a complicated and sensible quench protection system redundant. To expedite the use of such coils in a real power application the design and construction of a 10 kW laboratory generator demonstrator is set as an objective. Therefore, a pancake racetrack coil is designed for the usage in the stator system of such a demonstrator and wound without any insulation between the turns. The performance of this coil, especially under conduction cooled conditions below 77 K, is investigated. The first results in terms of effectiveness of the cooling system, recording the typical parameters of no-insulation coils and investigating the thermal and electrical behavior at dynamic load situations is presented.