Quench Heaters Research Articles

Overview of the Quench Heater Performance for MQXF, the Nb3Sn Low-<italic>β</italic> Quadrupole for the High Luminosity LHC

In the framework of the high-luminosity upgrade of the Large Hadron Collider, the U.S. LARP collaboration and CERN are jointly developing a 150 mm aperture Nb3Sn quadrupole for the LHC interaction regions. Due to the large stored energy density and the low copper stabilizer section, the quench protection of these magnets is particularly challenging, relying on a combination of quench heaters attached to the coil surface and coupling loss induced quench (CLIQ) units electrically connected to the coils. This paper summarizes the performance of the quench heater strips in different configurations relevant to machine operation. The analysis is focused on the inner layer quench heaters, where several heater strips failed during powering tests. Failure modes are discussed in order to address the technology issues and provide guidance for future tests.

Analysis of the Experimental Quench Propagation on a 2-km MgB2 Coil Up to 4 T

CEA Saclay, in collaboration with the French SMI Sigmaphi, has fabricated a 50-kg solenoid with a 2-km Columbus MgB 2 rectangular wire (3 × 0.7 mm²). The magnet was powered with 100 A at about 10 K and reached 4.2 T on the wire, with an external magnetic field of 3 T. A comparison between the protection and stability theoretical study and experimental results is presented. The quench propagation measurements have been performed at various temperatures, coil currents, and external fields. More than 20 quenches have been triggered using quench heaters mainly around the nominal design condition (10 K, 4 T, and 50 A/mm² of overall conductor current). These measurements values are compared to the results of the design calculations. The differences with the numerical model are analyzed, and a possible explanation of these differences is given by not taking into account real ground insulation thickness. The validation of the experimental parameters is necessary for designing the protection of high-field MgB2 magnets in the frame of our development program. The performances of recent MgB2 wires allow us to reach magnetic fields over 5 T.

Quench Protection Performance Measurements in the First MQXF Magnet Models

The European Organization for Nuclear Research (CERN) and U.S. LHC Accelerator Research Program (LARP) are jointly developing Nb $_3$ Sn quadrupole magnets to be installed in the LHC for its upgrade to higher luminosity. These magnets’ quench protection system will include a combination of quench heaters attached to the coil surfaces and coupling-loss-induced quench (CLIQ) units electrically connected to the magnets. Different protection elements have been characterized separately and simultaneously by implementing them on two 1.2-m-long model quadrupole magnets, tested at Fermi National Acceleration Laboratory and CERN, and one 4-m-long mirror magnet tested at Brookhaven Nation Laboratory. After analyzing the test data, their performances have been positively evaluated. Furthermore, the electrothermal transients occurring after a quench have been simulated with the LEDET software and the results are compared to experimental results. The preferred quench protection system configuration relies both on heaters and CLIQ. This solution is based on electrically robust components, achieves an effective reduction of the coils hot spot temperature after a quench, and offers increased redundancy against component failures.

Overview of the Performance of Quench Heaters for High-Current LHC Superconducting Magnets

Quench heaters are an essential part of the protection of all high-current large hadron collider (LHC) superconducting circuits. About 2000 dipole and quadrupole magnets are equipped with quench heaters in order to protect them against development of excessive voltage and overheating after a resistive transition. The quench heaters are made of stainless steel foil partially plated with copper and connected to 900 V capacitor bank discharge power supplies. During Hardware Commissioning campaigns and machine operation every quench heater discharge event is carefully analysed to detect a possible failure or a precursor of a failure, which could lead to damage of the heater or to the superconducting coils in subsequent discharges. This paper will briefly describe two different ways of quench heater data analysis and will present the heaters performance during the years 2008-2015. A summary of the quench heater fatigue test performed on a spare LHC main dipole magnet will also be given.

Quench Protection System Optimization for the High Luminosity LHC Nb $_3$Sn Quadrupoles

The upgrade of the large hadron collider to achieve higher luminosity requires the installation of twenty-four 150 mm aperture, 12 T, Nb 3 Sn quadrupole magnets close to the two interaction regions at ATLAS and CMS. The protection of these high-field magnets after a quench is particularly challenging due to the high stored energy density, which calls for a fast, effective, and reliable protection system. Three design options for the quench protection system of the inner triplet circuit are analyzed, including quench heaters attached to the coil's outer and inner layer, Coupling-Loss Induced Quench (CLIQ), and combinations of those. The discharge of the magnet circuit and the electromagnetic and thermal transients occurring in the coils are simulated by means of the TALES and LEDET programs. The sensitivity to strand parameters and the effects of several failure cases on the coil's hot-spot temperature and peak voltages to ground are assessed. A protection system based only on quench heaters attached to the outer layer can barely maintain the hot-spot temperature below the target limit and cannot guarantee the coil protection under failure scenarios. On the contrary, systems including either inner quench heaters or CLIQ are adequate to protect the coil under all realistic operation and failure scenarios. In particular, the option including outer quench heaters and CLIQ achieves lowest hot-spot temperatures, and highest redundancy and robustness.

Modeling of Interfilament Coupling Currents and Their Effect on Magnet Quench Protection

Variations in the transport current of a superconducting magnet cause several types of transitory losses. Due to its relatively short time constant, usually of the order of a few tens of milliseconds, interfilament coupling loss can have a significant effect on the coil protection against overheating after a quench. This loss is deposited in the strands and can facilitate a more homogeneous transition to the normal state of the coil turns. Furthermore, the presence of local interfilament coupling currents reduces the magnet's differential inductance, which in turn provokes a faster discharge of the transport current. The lumped-element dynamic electrothermal model of a superconducting magnet has been developed to reproduce these effects. Simulations are compared to experimental electrical transients and found in good agreement. After its validation, the model can be used for predicting the performance of quench protection systems based on energy extraction, quench heaters, the newly developed coupling-loss-induced quench protection system, or combinations of those. The impact of interfilament coupling loss on each protection system is discussed.

Next Generation of Quench Detection Systems for the High-Luminosity Upgrade of the LHC

The foreseen upgrade of the large hadron collider (LHC) for high-luminosity operation will incorporate a new generation of high field superconducting magnets. In particular, the current inner triplet magnets in LHC experiments A Toroidal LHC Apparatus (ATLAS) and Compact Muon Solenoid (CMS) in points 1 and 5 will be replaced by novel large aperture Nb 3 Sn quadrupole magnets. In addition, there will be a variety of new magnets based on NbTi conductors. For the magnet powering, the novel MgB 2 based superconducting links will be used, thus allowing the installation of sensitive equipment such as power converters in radiation-free areas of the LHC. The protection of the superconducting elements will be ensured by various elements such as quench heaters and the recently developed coupling-loss induced quench system, which are triggered by a dedicated set of quench detection systems. These custom-made systems are the result of a complete new development and adapted to the specific features of the newly installed superconducting elements. This concerns in particular the Nb 3 Sn based magnets, requiring an effective rejection of voltage spikes resulting from flux jumps and a dynamic setting of detection parameters when energizing the magnet. The new detection systems will be complemented by data acquisition systems, offering significantly higher sampling rates and resolution than previously installed systems.

Suitability of Different Quench Protection Methods for a 16 T Block-Type Nb3Sn Accelerator Dipole Magnet

Within the future circular collider study, a 100-km long circular hadron collider is being designed for 100 TeV center-of-mass collision energies. The design of the 16 T Nb 3 Sn bending dipole magnets is carried out within the EuroCirCol collaboration. Three different type of dipole designs have been developed, each aiming to be as compact as possible, accounting for the design criteria. Quench protection a critical aspect of the magnet design and potentially limits the magnet compactness. The EuroCirCol magnets were designed assuming a protection system with significantly improved efficiency compared to the present LHC dipole protection. In this paper, we consider present state-of-the-art quench protection technologies, such as quench heaters and CLIQ, and apply them into the designed 16 T Block-type dipole. Two different simulation models are used to estimate the magnet hotspot temperature and voltages after a quench and consequently estimate the suitability of the different methods.

Numerical simulation of quench protection for a 1.5 T persistent mode MgB2 conduction-cooled MRI magnet

The active quench protection of a 1.5 T MgB2 conduction-cooled MRI magnet operating in persistent current mode is considered. An active quench protection system relies on the detection of the resistive voltage developed in the magnet, which is used to trigger the external energizing of quench heaters located on the surfaces of all ten coil bundles. A numerical integration of the heat equation is used to determine the development of the temperature profile and the maximum temperature in the coil at the origin, or ‘hot spot’, of the quench. Both n-value of the superconductor and magnetoresistance of the wire are included in the simulations. An MgB2 wire manufactured by Hyper Tech Research, Inc. was used as the basis to model the wire for the simulations. With the proposed active quench protection system, the maximum temperature was limited to 200 K or less, which is considered low enough to prevent damage to the magnet. By substituting Glidcop for the Monel in the wire sheath or by increasing the thermal conductivity of the insulation, the margin for safe operation was further increased, the maximum temperature decreasing by more than 40 K. The strain on the MgB2 filaments is calculated using ANSYS, verifying that the stress and strain limits in the MgB2 superconductor and epoxy insulation are not exceeded.

Quench Protection of a 16-T Block-Coil Dipole Magnet for a 100-TeV Hadron Collider Using CLIQ

Protection against the effects of a quench is a crucial challenge for 16-T-class superconducting dipole magnets for a future 100-TeV Hadron collider. To avoid damage due to overheating of the coil's hot spot, heat generated during the quench has to be homogeneously distributed in the winding pack by quickly and uniformly transferring to the normal-state voluminous coil sections. Conventional protection systems rely on quench heaters placed on the outer surfaces of the coils. However, this technique has to confront significant challenges in order to achieve the fast transitions required by high magnetic field magnets. The recently developed coupling-loss-induced quench (CLIQ) utilizes interfilament coupling loss as an effective intrawire heat deposition mechanism, which, in principle, is faster than thermal diffusion. Furthermore, the CLIQ technology is based on simple and robust electrical components in contact with the coil only in a limited number of easily accessible and well-insulated points. Hence, expected occurrence of failure and electrical breakdown is significantly reduced. As a case study, the design of a CLIQ-based protection system for a 14-m-long 16-T Nb 3Sn block-coil dipole magnet is demonstrated here. Various magnet design features can be adjusted to improve CLIQ performance and optimize its integration in the magnet system. CLIQ provides future magnet designers with a solution for a very effective, yet electrically robust, quench protection system, resulting in better magnet performance and lower cost than would be possible with a traditional approach to magnet protection.

Retraining of the 1232 Main Dipole Magnets in the LHC

The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.

Study on Normal Zone Characteristics in a REBCO Insert Coil Induced by Quenches in an LTS Outsert Coil

In this paper, normal zone in a REBCO single-pancake coil induced by quenches in a low-temperature superconducting outsert coil is investigated in both experimental and numerical methods to discuss the quench protection of REBCO coils. The normal zone is experimentally clarified by measuring a partial voltage in the REBCO coil at temperatures from 30 K to 50 K during quenches of the outsert coil charging 5 T. Using practical fittings for the physical properties of the components of the REBCO coil in ranges of 0-5 T and 10-77 K, the numerical results have good agreement with the experimental results. The simulation reveals the heating distribution with initial temperatures from 10 K to 65 K, which indicates that the maximum temperature in a hot spot becomes higher for the lower initial temperature. Unexpectedly, the temperature distribution becomes rather homogeneous with an initial temperature of 65 K. It suggests that the hot spot at higher temperature has a lower risk of burning out. Finally, possible coil protections are discussed as the operation at the high temperature or the quench heater method to keep the REBCO coil at high temperature when a hot spot appears.

Progress in the Development and Construction of a 32-T Superconducting Magnet

The 32-T superconducting magnet is envisioned as a 15-T low-temperature superconductor (LTS) magnet combined with a separately powered REBCO high-temperature superconductor (HTS) insert configured as two coil stacks generating 17 T. Progress was made in all aspects of this project and is reported in this work. The design concept, which has been quite stable, is presented, as well as key elements from recent developments such as increased voltage standoff requirements. In both factory testing and installation at the NHMFL, the 15-T/250-mm-bore outer magnet built by Oxford Instruments met all specifications, including a ramp time of 1 h to full field. The test protocol included a deliberately induced full-field quench, releasing 7 MJ. After the helium level recovered, the magnet was ramped again in 1 h to full field, demonstrating full recovery. Helium boiloffs during normal operation and quench were observed, as well as the current and field decay during quench. The latter information serves as one of many inputs for the numerical quench code developed specifically to model quench in coupled LTS-HTS coils. Results from the 32-T quench analysis and implications for quench protection are summarized. All HTS conductor lengths were subjected to an extensive quality assurance (QA) protocol, and SuperPower has now delivered all required conductor lengths within specifications. A summary of the QA data and its implications are presented. The prototype coils, which are very similar in design to the 32-T REBCO coils but of reduced height, have now been impregnated with paraffin to address winding motion observed in previous testing. The prototype test protocol includes a study of the effectiveness of the quench heaters in the HTS coils in both a constant background field as provided by the actual 15-T LTS outer magnet for 32 T and, uniquely, in case the outer magnet is deliberately quenched.

Quench Detection Method for the Inductively Coupled Superconducting Magnets of KATRIN

The next-generation neutrino mass experiment KATRIN uses series of superconducting magnet systems. For the protection of the inductively coupled magnets of KATRIN, a distinct quench detection is essential. For example, the Cryogenic Pumping Section (CPS) of KATRIN has seven superconducting solenoids that are electrically connected in series. The quench detection for the magnet system is not trivial, because the inductive coupling effect between neighboring solenoids is not negligible, although the coupling coefficients are small and below 0.04. The electrical simulations show that a quench in the neighboring magnets can cause a high unbalancing signal in the quench detection system of the CPS, without inducing a quench in the CPS magnets. Therefore, a concept for the identification of a quench in one of the CPS magnets has been developed, using a combination of a global detector and two or more detectors based on the conventional bridge method and a programmable logic controller. This distinct quench detection helps activating quench heater effectively and minimizing unnecessary loss of liquid helium and operation time. This paper describes the concept of the quench detection method for the inductively coupled superconducting magnets of the CPS.

New Analysis Framework Software for the CERN Superconducting Magnet Test Facility

Since 2013, the existing but aging analysis tools that were routinely used for the large hadron collider (LHC) magnet series production measurement campaigns conducted at the CERN superconducting Magnet Test Facility (SM18) are being replaced by a novel open-data and user-driven analysis environment. This effort is running in parallel to the current development of magnet prototypes in the framework of the High Luminosity Upgrade of the CERN LHC (HL-LHC project). This R&D phase requires new features in the quench analysis software to cope with the dedicated or specific magnet tests (splice resistance, inductance, ac loss, Quench Heater efficiency, Hot Spot Temperature assessment, etc…), as well as a more open access to the mathematical routines and to the output results. The new data handling and analysis tools framework that is currently deployed is based on two pillars. First, the availability of the legacy proprietary raw data in an open and widely accessible format. Second, the new possibility for the user to process with the data through dedicated numerical tools and algorithms recently developed for data viewing, analysis, and formatted test result reports. In this paper, the initial analysis framework is described in terms of the acquisition system that produces data, the conversion tool that standardizes the file format, the new analysis tool that replaces the existing quench analysis software, and the database tool that archives the summary of every test. Finally, some statistics of the current situation are presented, based on facts and results of one year of analysis working within the superconducting magnet test facility.

Quench Protection Study of the Updated MQXF for the LHC Luminosity Upgrade (HiLumi LHC)

In 2023, the LHC luminosity will be increased, aiming at reaching 3000 fb-1 integrated over ten years. To obtain this target, new Nb3Sn low-β quadrupoles (MQXF) have been designed for the interaction regions. These magnets present a very large aperture (150 mm, to be compared with the 70 mm of the present NbTi quadrupoles) and a very large stored energy density (120 MJ/m3). For these reasons, quench protection is one of the most challenging aspects of the design of these magnets. In fact, protection studies of a previous design showed that the simulated hot spot temperature was very close to the maximum allowed limit of 350 K; this challenge motivated improvements in the current discharge modeling, taking into account the so-called dynamic effects on the apparent magnet inductance. Moreover, quench heaters design has been studied to be going into more details. In this study, a protection study of the updated MQXF is presented, benefiting from the experience gained by studying the previous design. As a result, a study of the voltages between turns in the magnet is also presented during both normal operation and most important failure scenarios.

Design Study of a 16-T Block Dipole for FCC

Author(s): Sabbi, G; Blomberg Ghini, J; Gourlay, SA; Marchevsky, M; Ravaioli, E; Ten Kate, H; Verweij, A; Wang, X | Abstract: The Future Circular Collider (FCC) study at CERN is investigating the design of a proton-proton collider with a center of mass energy of 100 TeV and a tunnel circumference of 100 km (FCC-hh). Nb3Sn arc dipoles with 50-mm aperture and 16-T operating field are required for this application. Among the possible magnetic layouts, block coils offer attractive features, in terms of conductor packing, separation between high-field and high-stress locations, use of flat cables, and simpler geometries for windings and parts. In order to assess these potential advantages, the HD series of block-coil models was developed at LBNL. These models achieved fields of 15-16 T in technology tests, and 13-14 T in accelerator relevant configurations, with bore diameters of 36-43 mm. In this paper, we discuss the implications of increasing the bore diameter to 50 mm, which is consistent with the latest FCC-hh design targets. A detailed quench protection analysis is performed using the new coupling-loss-based CLIQ system, expanding the safe parameter space with respect to the traditional approach based on quench heaters. Finally, alternative magnet design options, and further studies required to select among them, are outlined.

Advanced Quench Protection for the Nb3Sn Quadrupoles for the High Luminosity LHC

The goal of the High Luminosity LHC project is upgrading the LHC in order to increase its luminosity by a factor of five. To achieve this, 24 150-mm-aperture 12-T Nb 3Sn quadrupole magnets are to be installed close to the two interaction regions at ATLAS and CMS. This new generation of high-field magnets poses a significant challenge concerning the protection of the coils in the case of a quench. The very high stored energy per unit volume requires a fast and effective quench heating system in order to limit the hot-spot temperature and hence avoid damage due to overheating. Conventional protection systems based on quench heaters have a limited response time due to the thermal insulation between the heater and the coil. An advanced solution for the protection of high-field magnets is the coupling-loss induced quench (CLIQ) system, recently developed at CERN. Due to its fast intrawire energy-deposition mechanism, CLIQ is a very effective, yet electrically robust, quench protection system. Various protection scenarios, including quench heaters, CLIQ, or combinations of the two methods, are analyzed and discussed, with the aim of minimizing the coil's hot-spot temperature and thermal gradients during the discharge. The proposed design assures a fully redundant system.

First Implementation of the CLIQ Quench Protection System on a Full-Scale Accelerator Quadrupole Magnet

Author(s): Ravaioli, E; Bajas, H; Datskov, VI; Desbiolles, V; Feuvrier, J; Kirby, G; Maciejewski, M; Ten Kate, HHJ; Verweij, AP; Willering, G | Abstract: The coupling-loss induced quench system (CLIQ) is an innovative method for the protection of high-field superconducting magnets. With respect to the conventional method based on quench heaters, it offers significant advantages in terms of electrical robustness and energy-deposition velocity. Its effective intrawire heating mechanism targets a fast and homogeneous transition to the normal state of the winding pack, hence assuring a quick magnet discharge and avoiding overheating of the coil's hot spot. Furthermore, it is possible to implement CLIQ as a time- and cost-effective repair solution for the protection of existing magnets with broken quench heaters. After being successfully tested on model magnets of different geometries and made of different types of superconductor, CLIQ is now applied for the first time for the protection of a full-scale quadrupole magnet at the CERN magnet test facility. One aperture of a 3.4-m-long LHC matching quadrupole magnet is equipped with dedicated terminals to allow the connection of a CLIQ system. Experimental results convincingly show that CLIQ can protect this coil over the entire range of operating conditions. The complex electrothermal transients during a CLIQ discharge are successfully reproduced by means of a 2-D model. The test is part of the RD program of CLIQ quench protection systems, which has convincingly demonstrated the maturity of this technology and its effectiveness also for large-scale magnet systems. The proposed CLIQ-based solution for the quench protection of the LHC matching quadrupole magnet is now ready to be implemented in the LHC machine if needed.

Study of Quench Protection for the Nb3Sn Low-β Quadrupole for the LHC Luminosity Upgrade (HiLumi-LHC)

The HiLumi program is aiming to develop and build new Nb 3 Sn, high-field (12 T), and large-aperture (150 mm) superconducting quadrupoles, which will be inserted in the LHC interaction regions and will provide the final focusing of the beam, in the program of luminosity upgrade. The quench protection of these magnets is one of the most challenging aspects, mainly because of the large value of the magnet inductance (160 mH for the configuration with two 8-m-long magnets in series), of the large value of the stored magnetic energy density in the coils (0.12 J/mm 3 , a factor 2 larger than in the conventional NbTi quadrupoles) and of the use of Nb 3 Sn as a conductor, which has never been used for large accelerator magnets. Previous works have demonstrated that a “standard” conservative analysis, assuming quench heaters only on the coils' outer layer, gives high hot-spot temperature, close to the design limit (350 K). In this paper, a new study of quench protection is presented. The benefic effects of large dI/dt during the discharge and other dynamic effects are discussed together with options for having a partial coverage of the inner layer by quench heaters. The analysis is validated by experimental data from R&D Nb 3 Sn quadrupole magnets.