Fast Quench Research Articles

О возможности импульсного сверхпроводящего индуктивного накопителя энергии без внешнего коммутатора, использующего явление сверхбыстрого перехода

The phenomenon of ultrafast transition (fast quench) to the normal state is known for some types of multistrand superconducting cables. The apparent velocity of propagation of the normal zone in such cables exceeds 100 km/s. Based on the application of the phenomenon of ultrafast transition, a possible concept of a pulsed superconducting inductive energy storage without an external switch is discussed. The strengths and weaknesses of such a storage device are considered and preliminary estimates of a system with an energy of ~ 1 MJ are made.

Bi-Filar Coil Winding for Fast Quench Protection

Bi-Filar Coil Winding for Fast Quench Protection

Timescale of fast thermal quench based on general thermal diffusion induced by stochastic magnetic fields

Timescale of fast thermal quench based on general thermal diffusion induced by stochastic magnetic fields

Fast Quench Propagation Conductor for Protecting Canted Cos-Theta Magnets

Canted Cos-Theta (CCT) magnet design offers remarkable advantages such as a low number of parts and the ability to intercept with the formers the Lorenz forces acting on the windings. However, by principle, it is very challenging to design a self-protected CCT magnet, even with relatively low stored energy and conductor current density. This is predominantly due to the normal zone being unable to propagate along the magnet axial direction. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fast Quench Propagation Conductors (FQPCs) for quench protection of CCT magnets are proposed and studied. FQPC is a superconducting conductor carrying the magnet transport current and placed along the main axis of the CCT magnet in good thermal contact with the turns of the windings. FQPC is connected electrically in series with the CCT windings but electrically insulated at the thermal contacts by the electric insulation of the conductors. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The FQPCs aim to spread the normal zones in the CCT windings via a shorter axial path rather than only the path along CCT conductors and between them in the formers channels. Typically, ribs of the former inhibit axial quench propagation, and the FQPCs thermally connect CCT windings in the axial direction. The FQPCs quench due to the heat generated in the quenched turn and then act effectively like quench heaters powered by the magnet current. It means a completely passive system powered by the magnet energy that becomes inactive after magnet current decay. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Quench protection transients are calculated using a consecutive-simulation approach involving two software tools developed as part of the STEAM framework at CERN: a finite element (FE) based tool called FiQuS coupled with a finite difference (FD) based tool called LEDET. This approach allows for a three-dimensional (3D) quench simulation and introduces a great level of geometrical detail while maintaining a reasonable computational effort. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The benefits of the FQPCs depend on their number, placement, and duration of quench transient, which is affected by the CCT magnet size. These dependencies are studied in terms of the winding maximum temperature and voltage-to-ground that result from single, hot-spot-induced quenches in various locations in the windings.

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.

The timescale of thermal quench during disruptions in EAST

Since 2015, the timescale of thermal quench (TQ) during disruptions on the EAST tokamak has been examined using electron cyclotron emission and soft x-ray diagnostic systems. The database includes both major disruptions (MDs) and hot vertical displacement events (VDEs), where the TQ duration of the former is within 56–788 μs, and the latter is approximately within 100–3000 μs. In particular, for MDs, the lower bound of TQ duration, indicating the minimum durations at different current plateaus, decreases as the plasma current increases. This decrease is due to the connection length shortening and the plasma temperature increasing. For MDs, two typical TQ processes, single-stage TQ and double-stage TQ, are characterized by different magnetic perturbations. In single-stage TQ, a fast-loss stage is triggered by magnetic perturbation exceeding 4.3 × 10−3 T with a fast growth rate of 1.5 × 10−2 μs−1. In contrast, fast quench is triggered by a slightly smaller magnetic perturbation of 3.6 × 10−3 T in double-stage TQ, and the growth rate 5.3 × 10−3 μs−1 is an order of magnitude smaller than single-stage TQ. For hot VDEs, the plasma temperature collapses step by step from the edge to the core, and every progressive collapse corresponds to a magnetic perturbation, whose growth rate is approximately equal to or less than double-stage TQ. The whole process of TQ energy release can be divided into the transport in a stochastic field within the separatrix and in the scrape-off layer and, according to the typical parameters of EAST, TQ duration in MDs is roughly estimated to be 245 μs by an approximate formula, which is consistent with the experimental results.

Shear transformations in metallic glasses without excessive and predefinable defects

Plastic flow in metallic glasses (MGs) is known to be mediated by shear transformations (STs), which have been hypothesized to preferentially initiate from identifiable local "defect" regions with loose atomic packing. Here we show that the above idea is incorrect, i.e., STs do not arise from signature structural defects that can be recognized a priori. This conclusion is reached via a realistic MG model obtained by combining molecular dynamics (MD) and Monte Carlo simulations, achieving liquid solidification at an effective cooling rate as slow as 500 K/s to approach that typical in experiments for producing bulk MGs. At shear stresses before global yielding, only about 2% of the total atoms participate in STs, each event involving typically ~10 atoms. These observations rectify the excessive content of "liquid-like regions" retained from unrealistically fast quench in MD-produced glass models. Our findings also shed light on the indeterministic aspect of the ST sites/zones, which emerge with varying spatial locations and distribution depending on specific mechanical loading conditions.

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

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

Fast Discharging Behavior of High Temperature Superconducting Coils With Copper Rings and Plates

Fast energy extraction using dump resistances is an effective method for quench protection of high temperature superconducting (HTS) magnets. Copper frames are often applied in HTS magnets for conduction cooling and mechanical support. Previous studies have shown that copper plates can accelerate the energy release of HTS coils during discharging operations with dump resistance, which is favorable for fast quench protection. Copper rings distributed at the inner and outer diameters of HTS coils can provide a strong mechanical support for the possible electromagnetic strain in high magnetic fields. This paper studies the effect of copper rings and plates on fast discharging process of an insulated HTS double pancake coil by finite element method. An optimized structure composed of copper rings and plates is proposed, and its effect on fast discharge is analyzed. The results show that copper plates show better performance than copper rings in accelerating energy release and reducing hot spot temperature of the coil. During discharging process, the optimized structure can absorb considerable energy from the HTS coil and significantly reduce the hot spot temperature. The optimized structure is a promising alternative for fast quench protection of HTS magnets.

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.

Experimental observations of marginal criticality in granular materials

SignificanceAmorphous materials, such as grains, foams, colloids, and glasses, are ubiquitous in nature and our daily life. They can undergo glass transitions or jamming transitions to obtain rigidity either by fast quench or compression, but show subtle changes in the structures compared to the liquid states or liquid-like states. Recent progress on the first-principle replica theory unifies the glass transition and the jamming transition and points out the marginal phase with fractal free-energy landscape within the stable glass phase. Independently, marginal stability analysis predicts the relations between the exponents of the marginal phase. Here, we perform experiments with photoelastic disks and provide direct evidence of these theories in real-world amorphous materials.

Overview of recent experimental results from the ADITYA-U tokamak

Since the 2018 IAEA-FEC conference, in addition to expanding the parameter horizons of the ADITYA-U machine, emphasis has been given to dedicated experiments on inductively driven particle injection (IPI) for disruption studies, runaway electron (RE) dynamics and mitigation, plasma rotation reversal, radiative-improved modes using Ne and Ar injection, modulation of magneto–hydrodynamic modes, edge turbulence using periodic gas puffs and electrode biasing (E-B). Plasma parameters close to the design parameters of circular plasmas with H2 and D2 as fuel have been realized, and the shaped plasma operation has also been initiated. Consistent plasma discharges having I P ∼ 100–210 kA, t ∼ 300–400 ms, n e ∼ 3–6 × 1019 m−3, core T e ∼ 300–500 eV were achieved with a maximum B T of ∼1.5 T. The enhanced plasma parameters are the outcome of repeated cycles of baking (135 °C), followed by extensive wall conditioning, which includes pulsed glow discharge cleaning in H, He and Ar–H mixture, and lithiumization. A higher confinement time has been observed in D2 compared to H2 plasmas. Furthermore, shaped plasmas are attempted for the first time in ADITYA-U. A first of its kind inductively driven particle injection for disruption mitigation studies has been developed and operated. The injection of solid particles into the plasma core leads to a fast current quench. Two pulses of electron cyclotron resonance wave at 42 GHz are launched in a single discharge: one pulse is used for pre-ionization and the second for heating. In a novel approach, a positively biased electrode is used to confine REs after discharge termination. E-B is also used for controlling the rotation of drift-tearing modes by changing the plasma rotation. Cold pulse propagation and signatures of detachment are observed during the injection of short gas puffs. A correlation between the plasma toroidal rotation and the total radiated power has been observed with neon gas injection-induced improved confinement modes.

Influence of a nonuniform thermal quench and circular polarized radiation on spontaneous current generation in superconducting rings

We theoretically study the nonequilibrium dynamics of the order parameter of a superconducting ring inhomogeneously quenched through its transition temperature. Numerical simulations based on spectral decomposition of the time-dependent Ginzburg-Landau equation reveal that current-carrying superconducting states can be generated in the ring under certain fast local temperature quench conditions. We also show that illumination of the ring with a circularly polarized electromagnetic radiation during rapid cooling strongly promotes the generation of current-carrying states with rotation directions controlled by the helicity of the radiation field.

Defect Saturation in a Rapidly Quenched Bose Gas

We investigate the saturation of defect density in an atomic Bose gas rapidly cooled into a superfluid phase. The number of quantum vortices, which are spontaneously created in the quenched gas, exhibits a Poissonian distribution not only for a slow quench in the Kibble-Zurek (KZ) scaling regime but also for a fast quench, in which case the mean vortex number is saturated. This shows that the saturation is not caused by destructive vortex collisions, but by the early-time coarsening in an emerging condensate, which is further supported by the observation that the condensate growth lags the quenching in the saturation regime. Our results demonstrate that the defect saturation is an effect beyond the KZ mechanism, opening a path for studying critical phase transition dynamics using the defect number distribution.

In Situ X-ray Diffraction at High Temperatures: Formation of Ca2SiO4 and Ternesite in Recycled Autoclaved Aerated Concrete

This study provides an insight into possible recycling processes for autoclaved aerated concrete (AAC) at low temperatures (&lt;1000 °C). Belite binders were synthesized from wastes of AAC by the addition of CaCO3 and adaption of the molar CaO/SiO2 (C/S ratio) in the range of 2 to 2.5. An in situ XRD study performed during heating up to 1000 °C and subsequent quenching to room temperature evidenced the formation of ternesite besides C2S in sulfate-containing systems. Several factors influencing the reaction kinetics and the evolution of the phase composition were investigated thoroughly. Increased sulfate content and dwelling time during heating increase the ternesite content and promote the formation of highly crystalline α’H-C2S. The C/S-ratio of the starting materials has to be adjusted to the sulfate content in order to prevent the formation of ternesite at the expense of C2S. Ternesite remains stable during quenching to room temperature or even increases in amount, except in cases of very low cooling rates or high residual quartz contents (C/S-ratio ≤ 2). Temperature and range of α’H-C2S to β-C2S phase transition on quenching strongly depend on the cooling rate. The onset temperature for β-C2S formation varies between 540 °C (slow quench) and 450 °C (fast quench). Thermal expansion coefficients of ternesite are calculated showing similarity with C2S. The incorporation of CaSO4 modules in the structure switches the direction of maximum compression.

Molecular and micro-scale heterogeneities in Raman modes of a relaxing polymer glass

We have used Raman spectroscopy to study relaxation dynamics at two different length scales, molecular level and micro-scale in order to probe the presence of cooperative rearranging regions in a polymer glass. Response to slow thermal cycles and fast quench through the glass transition temperature (T g) is analyzed for film and unprocessed forms of polyvinyl acetate (PVAc). In PVAc film, enhanced disorder and molecular mobility lead to peak broadening by about a factor of 10 compared to unprocessed PVAc. Thermal cycles (10 K min−1) produce hysteresis in integrated Raman peak intensity (loop area ). values of film are two orders of magnitude more than unprocessed, indicating more configurational mosaics with higher interfacial energy dissipations. Ageing after 60 K min−1 quench manifests as heterogeneous molecular dynamics of film Raman modes with significant peak-width variations, differentiating high mobility and low mobility modes. Two-dimensional mapping of film Raman modes after quench reveal micro-scale clusters of average size ≈250 molecules having fractal boundaries with fractal dimension d f = 1.5, resembling d f of percolation clusters below percolation threshold. During thermal cycling and relaxation after a quench, cooperative segmental dynamics with large correlations between skeletal C–C stretch and side branch modes is observed. The observations are analyzed in the context of the random first order transition theory of glasses, which attributes heterogeneous relaxations in glasses to the presence of clusters of variable configurational states.

Suppression of runaway current by magnetic energy transfer in J-TEXT

For disruptions without mitigation, a large amount of thermal energy and poloidal magnetic energy will be dissipated inside the vacuum vessel (VV). A slow current quench may be accompanied by a large halo current, while a fast current quench often causes large eddy current, which will result in electromagnetic force. At the same time, fast current quench will induce strong toroidal electric field, which will result in a large fraction of runaway current and the hitting of runaway beam on first wall. The disruption mitigation is essential for large scale tokamak. The existing methods to mitigate disruptions, such as massive gas injection and resonant magnetic perturbations, are aimed at increasing the runaway generation threshold or the lose rate of runaway electrons. It may not work for ITER with Ip = 15 MA operation. The root of runaway generation is the large toroidal electric field induced by fast current quench and the large avalanche factor with high plasma current. The reduction of toroidal electric field is favor for the runaway suppression. The magnetic energy transfer (MET) based on electromagnetic coupling for disruption mitigation has been proposed on J-TEXT. It has the advantage of transferring the magnetic energy to outside of vessel by the electromagnetic coupling. It accelerates the current quench (CQ) rate and reduces the toroidal electric field at the same time. The runaway current has been suppressed by the MET system on J-TEXT. The experimental results show that the MET can reduce the energy dissipated in the VV by 20 % through transferring of energy to outside of VV. The MET can increase the CQ rate about 50.7 % and decrease the loop voltage about 35.3 %. The MET provides a new idea to transfer the magnetic energy and to suppress runaway current for disruption mitigation in future devices.

Low-temperature statistical mechanics of the Quantizer problem: Fast quenching and equilibrium cooling of the three-dimensional Voronoi liquid

The quantizer problem is a tessellation optimization problem where point configurations are identified such that the Voronoi cells minimize the second moment of the volume distribution. While the ground state (optimal state) in 3D is almost certainly the body-centered cubic lattice, disordered and effectively hyperuniform states with energies very close to the ground state exist that result as stable states in an evolution through the geometric Lloyd's algorithm [M. A. Klatt et al. Nat. Commun. 10, 811 (2019)]. When considered as a statistical mechanics problem at finite temperature, the same system has been termed the "Voronoi liquid" by Ruscher, Baschnagel, and Farago [Europhys. Lett. 112, 66003 (2015)]. Here, we investigate the cooling behavior of the Voronoi liquid with a particular view to the stability of the effectively hyperuniform disordered state. As a confirmation of the results by Ruscher et al., we observe, by both molecular dynamics and Monte Carlo simulations, that upon slow quasi-static equilibrium cooling, the Voronoi liquid crystallizes from a disordered configuration into the body-centered cubic configuration. By contrast, upon sufficiently fast non-equilibrium cooling (and not just in the limit of a maximally fast quench), the Voronoi liquid adopts similar states as the effectively hyperuniform inherent structures identified by Klatt et al. and prevents the ordering transition into a body-centered cubic ordered structure. This result is in line with the geometric intuition that the geometric Lloyd's algorithm corresponds to a type of fast quench.

On-Demand Optical Generation of Single Flux Quanta.

Superconductors can host quantized magnetic flux tubes surrounded by supercurrents, called Abrikosov vortices. Vortex penetration into a superconducting film is usually limited to its edges and triggered by external magnetic fields or local electrical currents. With a view to novel research directions in quantum computation, the possibility to generate and control single flux quanta in situ is thus challenging. We introduce a far-field optical method to sculpt the magnetic flux or generate permanent single vortices at any desired position in a superconductor. It is based on a fast quench following the absorption of a tightly focused laser pulse that locally heats the superconductor above its critical temperature. We achieve ex-nihilo creation of a single vortex pinned at the center of the hotspot, while its counterpart opposite flux is trapped tens of micrometers away at its boundaries. Our method paves the way to optical operation of Josephson transport with single flux quanta.

Experimental study on temperature distribution measurement of an optical fiber encapsulated coil in liquid nitrogen

Fast quench detection technique is extremely important for high temperature superconducting (HTS) applications, especially HTS magnets. As one of potential candidates, the method based on distributed optical fiber sensors were suggested recently. To keep HTS tape structure intact and reduce thermal propagation time from HTS tape to optical fiber, a method that optical fiber is encapsulated in HTS tape edge along the length direction could be satisfied. In this paper, an optical fiber encapsulated tape (OF-tape) was successfully fabricated. To verify the feasibility of temperature measurement for this tape, a coil wound with OF-tape and a distributed temperature sensor (DTS) system were prepared. The main results show that temperature of the coil can be measured accurately in air and in liquid nitrogen. After suffering impulse currents with peak values of 570 A and durations of 1, 2, and 3 s, temperature rises of the coil are 98.5, 137.8, and 271.0 K, respectively. Moreover, the highest temperature appears from 3.6 m to 21.7 m of the coil when it suffers the impulse current of 460 A/3 s.