Passive Quench Research Articles

Charging delay elimination of solder impregnated HTS coils with specific excitation current

No-insulation (NI) coil has been recognized as the most practical solution at present to achieve ultra-high magnetic field with the REBCO high temperature superconductor thanks to its passive quench protection mechanism which is originated from the inter-turn current bypass. However, for the NI technique, one of the most important obstacles to a more general application is the field delay which is also a consequence of the lack of inter-turn insulation. The proportional and integral (PI) active feedback control of power supply has been developed to achieve a designed field ramping rate. The efficiency of this method could however be affected by the measurement accuracy of measuring equipment, sampling frequency, control accuracy of power supply and other factors. In this manuscript, we tried to use a more fundamental method to mitigate the field delay. The point is, though unlike in insulated coils the field generated is not proportional to coil current in NI coils, they do have a certain linear relation for a certain coil. Based on the lumped circuit model, the current charging curve corresponding to a desired field excitation could be calculated for a NI coil. We verified this method on several solder impregnated no-insulation coils (SINoInCs) to excite their field with different rates, for which the field delay with normal charging method could be very large because of the very low inter-turn resistance. The test results show that this kind of fast excitation method could successfully achieve the desired field with high accuracy and mitigate the field delay from 130 s to almost 0 s. Besides, the large overshoot current introduced by the fast charging does not quench the coils even with an overshoot current which is almost double of the coils’ operating current.

Quench Protection Study of a 14 T Conduction-Cooled Magnet Built With Nb3Sn and NbTi Superconducting Coils for PPMS

A 14 T conduction-cooled superconducting magnet with a clear cold bore of 50 mm in diameter is designed and fabricated for a physical property measurement system. The magnet is built with six Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils and five NbTi coils arranged coaxially. To reliably protect the 14 T magnet, a passive quench protection scheme is developed, including a novel coil subdivision method and heater network design. The novel coil subdivision method mixes a NbTi coil and an Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil into the same subdivision to reduce the hot-spot temperature of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil. Different heaters parameters are compared and analyzed to obtain a lower hot-spot temperature. In addition, an efficient way of raising the ratio of copper to superconductor in the superconducting wires is used to reduce the hot-spot temperature of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils in the low magnetic field region. An in-house quench simulation code in MATLAB, including a finite difference method for the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils in the low magnetic field region and a quench ellipsoid propagation model for the other coils, has been developed. This article describes the details of the passive quench protection scheme and presents the quench simulation results.

Design of a Canted-Cosine-Theta Orbit Corrector for the High Luminosity LHC

The High Luminosity LHC requires dipole orbit correctors grouped in double aperture magnet assemblies. They provide a field of 3.1 T at 100 A in an aperture of 70 mm. The current standard design is a classical cosine-theta layout made with ribbon cable. However, the electric insulation of this cable is not radiation-resistant enough to withstand the radiation load expected in the coming years of LHC operation. A new design, based on a cable with polyimide insulator, that can replace the existing orbit correctors, is needed. The challenge is to design a magnet that fits directly into the existing positions and that can operate with the same busbars, passive quench protection, and power supplies. The new orbit corrector design meets high requirements on the field quality while keeping within the same mechanical volume and maximum excitation current. A collaboration of Swedish universities and Swedish industry has been formed for the development and production of a prototype magnet following a concurrent engineering methodology to reduce the time needed to produce a CCT magnet. The magnet has a 1 m long CCT dipole layout consisting of two coils. The superconductor is a commercially available 0.33 mm wire with polyimide insulation in a 6-around-1 cable. The channels in the coil formers, that determine the CCT layout, allow for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2\times 5$</tex-math></inline-formula> cable layers. A total of 70 windings makes that the coil current can be kept below 100 A. We will present the detailed design and preliminary quench simulations.

Differential Quench and Reset Circuit for Single-Photon Avalanche Diodes

A differential quench and reset (QR) configuration for single-photon avalanche diodes (SPADs) is proposed and investigated in this work. Compared to the traditional single QR configuration in which only one QR circuit is connected to either the cathode or anode of the SPAD, the differential QR configuration consists of two QR circuits to quench and reset through both the cathode and anode terminals. Using a SPAD fabricated in a 65 nm CMOS process, the measurement results of the traditional single passive quench and reset (SPQR) circuit and the proposed differential passive quench and reset (DPQR) circuit shows that the SPAD with the DPQR circuit presented a reduced reset time, an improved timing performance, an increased count rate and a decreased afterpulsing. In addition, the differential output pair from the DPQR circuit has the potential to increase the signal-to-noise ratio of the detection system due to its ability to reject common-mode noise and interference.

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.

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.

Quench Protection Study of Superconducting Magnets for the Materials Plasma Exposure Experiment

To advance the understanding of plasma material interactions, the Material Plasma Exposure eXperiment (MPEX) is a new linear plasma device that will generate and deliver plasma relevant to future fusion reactor divertors. The operation of MPEX is planned to be steady-state in order to facilitate high fluence exposures of plasma facing materials and components. The desire for steady-state operation along with the magnetic field requires the utilization of superconducting coils. The superconducting magnet system for MPEX has been developed. The baseline model has six superconducting magnet and one room-temperature magnet subsystems. In order to protect multiple superconducting magnet systems, quench analysis was carried out to determine the best protection approach for each magnet type. Because the mutual inductance accounts for approximately 35% of the stored energy in the entire system, this must be considered when determining the peak voltages and temperatures during a quench. Two approaches for passive quench protection are considered: (1) self-protecting magnets and (2) use of diodes to sub-divide the coils. For both approaches, active quench detection will be used to ensure all coils are de-energized in the event of a quench. Results of the quench analysis for several quench scenarios are presented.

Test Results for a Superconducting 28-GHz Ion Source Magnet for FRIB

The superconducting ECR source magnet for the Facility for Rare Isotope Beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL). The 28-GHz NbTi ion source magnet features a sextupole-in-solenoids configuration, which is comparable to the VENUS ECR magnet operated at LBNL. A shell-based support structure using bladders and keys has been incorporated into the design to allow for adjustments of the preload and reversibility of the magnet assembly process. The magnet has been assembled and successfully tested to operational currents at LBNL. This paper describes the basic design of the magnet and the passive quench protection system. The test results are also presented, including the quench behavior of the magnet, the training performance, and the magnetic measurement results.

Post-Quench electromechanical analysis of 1.5 T whole body clinical MRI system

A 1.5 T superconducting magnet has been designed for the whole-body clinical MRI scanner. The stored energy (∼4.5 MJ) of the magnet if released during a quench, can adversely affect the coil by raising its temperature and the associated voltage across the coil. Any quench in the MRI magnet induces an eddy current on various components of the magnet system such as bobbin, thermal radiation shield, etc. A passive quench protection scheme has been designed and simulated for the MRI magnet. The hot-spot temperature and the peak voltage in the magnet respectively are 136 K and 2.15 kV. The quench induced eddy current and the associated mechanical stresses have also been simulated for the various components. The peak density of the eddy current on the magnet bobbin and the thermal radiation shield are 375.5 A/cm2 and 2316 A/cm2 respectively. Whereas the peak mechanical stresses are 40.48 MPa and 11 MPa for the bobbin and the thermal radiation shield respectively. This paper briefly discusses the quench protection scheme, quench-induced eddy current and its associated mechanical stresses on various components of the magnet system.

ICED—Inductively Coupled Energy Dissipater for Future High-Field Accelerator Magnets

Future high-field accelerator magnets, like the ones foreseen in the design study of the FCC project and for the EuCARD2 “Future Magnets” program, operate with magnetic fields in the range of 16-20 T. For such magnets the energy density is higher than in the accelerator magnets at present in operation, posing a challenge for the quench protection. Traditionally, quench protection has relied on generating large normal zones in the coil by firing quench protection heaters. The increase of the coil internal resistance results in a fast current decay. This paper introduces the Inductively Coupled Energy Dissipater (ICED) system, based on low resistance loops, which are inductively coupled with the coil. These loops greatly accelerate the current decay by rapidly extracting the energy from the coil, thereby lowering its peak temperature. Because of the potential reduction in stabilizer volume within the conductor, ICED may enable higher engineering current densities in the coil than with the protection relying entirely on dissipating the magnet's energy in the windings. The efficiency of ICED as a passive quench protection system is studied in this paper. We present the effect of such protection structure, on the field quality during standard powering of the magnets and on the cryogenic system. We study electromagnetic forces in the loops and mechanically stable geometric locations within the magnet structure. For the proof of the concept, this system has been employed in Feather-M2 dipole demonstrator. We compare our modeling approach to results gained from a cryogenic test.

Voltage Characteristics of Diodes Used for Passive Quench Protection of Low-Current Magnets

Cold diodes and resistors in parallel with the coils are keys components in the passive quench protection system of low-current (high inductance) superconducting magnets. The diodes prevent current from flowing in the circuits that are in parallel with sections of the superconducting coil when the magnet is being charged or discharged. The use of diodes and resistors in parallel with the superconducting coil sections reduce the peak voltages to ground and, in some cases, the hot-spot temperature in the magnet during a quench. This paper presents measurements of the onset (low current) forward voltage of several power diodes as a function of temperature and magnetic field.

Superconducting Solenoids for RF Accelerators and Electron Guns

Compact solenoids are applied at an increasing rate for beam focusing in superconducting RF accelerating structures, for instance in secondary ion beam linacs and for free electron lasers. High field solenoids with a center field of 7.9 T for the HIE-ISOLDE high-beta cryomodules at CERN are currently being designed and manufactured at Danfysik. NbTi coils and a soft iron yoke are carefully designed for operation in a LHe bath at a temperature of 4.5 K at field integral requirements of ≤ 13.5 T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> m. The quenching characteristics of this solenoid have been studied and simulated, and a passive quench protection circuit is part of the solenoid design. The yoke outer diameter is 200 mm; the total length 312 mm. An HTS solenoid based on second-generation high-temperature superconducting technology was designed, built, tested, and delivered by Danfysik to the free electron laser project of the University of Wisconsin. The compact 136-mm-long HTS solenoid with a center field of 0.2 T operates in the temperature range between 5 and 70 K. The field integral is 3.1 T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> mm with very small integrated field errors. Conduction cooling of the compact solenoid makes it easy to assemble and operate very close to the RF cavity.

A Passive Quench Protection Design for the 9.4 T MRI Superconducting Magnet

A passive quench protection design of the 9.4 T whole-body magnetic resonance imaging superconducting magnet is proposed. The design of the coil subdivision with shunt resistors is introduced. The selection of the configuration of the heater network is detailed. The optimization of the geometric parameter of the heater strips and the thickness of the insulation binding outside the heater strips are discussed. A winding sequence that could accelerate the quench propagation in the compensating coil is proposed. The calculation results show that the optimized quench protection design can guarantee the safety of the magnet in the case of any coil as the quench initiation coil.

MuCool Superconducting Solenoid Quench Simulations and Test Stand at FNAL

Fabrication and preparation for test of the MuCool superconducting solenoid are now in progress. The solenoid's passive quench protection system is based on cold diodes and shunt resistors. The solenoid does not have heaters, and quench propagation relies on the superconductor quenching and the subsequent “quench back” effect caused by eddy currents in the coil's Al mandrel. The solenoid has a very large inductance of ~600 H and the stored energy is 100% dissipated into the cold mass during a quench. This makes the solenoid protection a challenging task. This paper presents the quench analysis of the solenoid based on a 3-D FEA solution of the coupled transient electromagnetic and thermal properties during the quench. The simulations used the Vector Fields QUENCH code. A new test facility, the solenoid test stand (STS), is being built at Fermilab to test these coils. One of the critical issues regarding the STS is the fringe field produced by the magnet under test, which interacts with the surrounding equipment. In this paper, we present the stray-field analysis and the corresponding magnetic forces. The STS includes a sophisticated DAQ system to carefully monitor quench events and temperatures.

Quench Protection Design of a 1.5 T Superconducting MRI Magnet

A 1.5 T superconducting MRI magnet has been developed in our laboratory. A passive quench protection system is employed to avoid the damage through the quench event. The coils are subdivided into several groups and a heater network is implemented accordingly. With the control volume method, the numerical model of the quench time is introduced. Different design schemes of the heater strip are compared. The simulation results of currents and voltages are illustrated and the temperature rise of the coils and the heaters are discussed.

Quench Analysis of MICE Spectrometer Superconducting Solenoid

MICE superconducting spectrometer solenoids fabrication and tests are in progress now. First tests of the Spectrometer Solenoid discovered some issues which could be related to the chosen passive quench protection system. Both solenoids do not have heaters and quench propagation relied on the “quench back” effect, cold diodes, and shunt resistors. The solenoids have very large inductances and stored energy which is 100% dissipated in the cold mass during a quench. This makes their protection a challenging task. The paper presents the quench analysis of these solenoids based on 3D FEA solution of coupled transient electromagnetic and thermal problems. The simulations used the Vector Fields QUENCH code. It is shown that in some quench scenarios, the quench propagation is relatively slow and some areas can be overheated. We describe ways of improving the solenoids' quench protection in order to reduce the risk of possible failure.

The Role of Quench-Back in the Passive Quench Protection of Uncoupled Solenoids in Series With and Without Coil Sub-Division

This paper is the final paper in a series of papers that discusses passive quench protection for high inductance solenoid magnets. This report describes how passive quench protection system may be applied to superconducting magnets that are connected in series but not inductively coupled. Previous papers have discussed the role of magnet sub-division and quench back from a conductive mandrel in reducing the hot-spot temperature and the peak coil voltages to ground. When magnets are connected in series, quench-back from a conductive mandrel can cause other magnets in a string to quench even without inductive coupling between magnets. The magnet mandrels must be well coupled to the magnet circuit that is being quenched. When magnet circuit sub-division is employed to reduce the voltages-to-ground within magnets, the resistance across the subdivision becomes the most important factor in the successful quenching of the magnet string.

The Role of Quench-Back in the Passive Quench Protection of Long Solenoids With Coil Sub-Division

This paper describes how a passive quench protection system can be applied to long superconducting solenoid magnets. When a solenoid coil is long compared to its thickness, the magnet quench process will be dominated by the time needed for quench propagation along the magnet length. Quench-back will permit a long magnet to quench more rapidly in a passive way. Quench-back from a conductive (low resistivity) mandrel is essential for spreading the quench along the length of a magnet. The mandrel must be inductively coupled to the magnet circuit that is being quenched. Current induced in the mandrel by di/dt in the magnet produces heat in the mandrel, which in turn causes the superconducting coil wound on the mandrel to quench. Sub-division is often employed to reduce the voltages to ground within the coil. This paper explores when it is possible for quench-back to be employed for passive quench protection. The role of sub-division of the coil is discussed for long magnets.

Numerical Study on Quench Process in Multi-Sectioned Adiabatic Superconducting Electromagnetic Iron Separator

A two-dimensional quench simulation model was developed for the Superconducting Electromagnetic Iron Separator (SEIS) system, which is designed to separate small pieces of ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIS coil adopted passive quench protection system with four-sectioned arrangement, each shunted with four diodes. The aluminum slices, with 99.99% purity and 0.5 mm × 12 mm cross section dimension, working as quench propagator, were clothed on the inner and the outer surfaces of the coil. The minimum quench energy, the temporal variations of current, voltage and hot spot temperature rise of the coil were analysed. Furthermore, the coil stress during winding, cool-down, charging and quench process was also included in this paper. The simulation results demonstrated that the existing protection system could guarantee the SEIS magnet experience no fatal damage during quench.

Quench Protection for the MICE Cooling Channel Coupling Magnet

This paper describes the passive quench protection system selected for the muon ionization cooling experiment (MICE) cooling channel coupling magnet. The MICE coupling magnet will employ two methods of quench protection simultaneously. The most important method of quench protection in the coupling magnet is the subdivision of the coil. Cold diodes and resistors are put across the subdivisions to reduce both the voltage to ground and the hot-spot temperature. The second method of quench protection is quench-back from the mandrel, which speeds up the spread of the normal region within the coils. Combining quench back with coil subdivision will reduce the hot spot temperature further. This paper explores the effect on the quench process of the number of coil sub-divisions, the quench propagation velocity within the magnet, and the shunt resistance.