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One of the most challenging problems of no-insulation (NI) REBCO pancake coils is mechanical and thermal protection. Particularly, pancake coils suffer high stress during a local-normal state transition (quench event). One solution is a magnetic dam, which is merely NI windings with a few turns. The effectiveness of magnetic dams by 4-mm-wide NI windings was demonstrated numerically in the previous study. The effectiveness would be different when the REBCO tapes with different widths are employed. Therefore, in this article, the electromagnetic behaviors of NI REBCO pancake coils with the magnetic dam of 12-mm-wide REBCO tape are investigated numerically. The charging and the normal-state transition are simulated. It is demonstrated that the 4-mm-wide magnetic dam works more effectively due to the less screening current in the 4-mm-wide magnetic dam than the 12-mm-wide magnetic dam in this case.

The normal zone propagation velocity (NZPV) of three families of REBCO tape architectures designed for superconducting fault current limiters and to be used in high voltage direct current transmission systems has been measured experimentally in liquid nitrogen at atmospheric pressure. The measured NZPVs span more than three orders of magnitude depending on the tape architectures. Numerical simulations based on finite elements allow us to reproduce the experiments well. The dynamic current transfer length (CTL) extracted from the numerical simulations was found to be the dominating characteristic length determining the NZPV instead of the thermal diffusion length. We therefore propose a simple analytical model, whose key parameters are the dynamic CTL, the heat capacity and the resistive losses in the metallic layers, to calculate the NZPV.

Thermalization is an elusive phenomenon in quantum mechanics. Since according to the AdS/CFT correspondence, a black hole in the bulk spacetime is dual to a thermal state in the boundary CFT, thermalization in the CFT is dual to black hole formation in AdS. Thus, understanding quantum thermalization is likely a key component in understanding the information paradox—the contradiction between QFT and general relativity occurring when a black hole seemingly erases the information of whatever went into creating it. In this thesis we investigate different aspects of quantum thermalization in simple field theories that have conjectured holographic duals, or more specifically, free large N singlet models. Since such theories are free and hence integrable, thermalization is more subtle but nevertheless appears in different forms. We investigate the late-time quench dynamics of a version of the O(N) vector model with probes such as the effective density matrix and the spectral density function. We refine an operator thermalization hypothesis and explore its consequences in different spacetime dimensions in general large N singlet models. We also discuss the prospect of using thermal mixing in the boundary theory as a diagnostic of strong gravity in the bulk.

The fast thermal and electromagnetic transients that occur in a superconducting magnet in case of a quench have the potential of generating large mechanical stresses both in the superconducting coils and in the magnet structure. While the investigation of such quench loads should generally be conducted to ensure a safe operation of the system, its importance is greatly enlarged in the case of high-field magnets based on strain sensitive superconductors. For these, a rigorous analysis of the magnet mechanics during a quench becomes critical. The scope of this work is hence to bring, for the first time, a detailed understanding of the three-dimensional mechanical behavior of a Nb3Sn accelerator magnet during a quench discharge. The study relies on the use of finite element models, where various multi-domain simulations are employed together to solve the coupled physics of the problem. Our analysis elaborates on the case study of the new MQXF quadrupole magnet, currently being developed for the high-luminosity upgrade of the LHC. Notably, we could find a very good agreement between the results of the simulation and experimental data from full-scale magnet tests. The validated model confirms the appearance of new peak stresses in the superconducting coils. An increase in the most relevant transverse coil stresses of 20–40 MPa with respect to the values after magnet cool-down has been found for the examined case., Peer Reviewed, "Article signat per 13 autors/es: J Ferradas Troitino, H Bajas, L Bianchi, B Castaldo, P Ferracin, M Guinchard, S Izquierdo, J V Lorenzo, F Mangiarotti, J C Perez, E Takala, G Vallone and C Senatore", Postprint (published version)

We experimentally studied the quench properties of REBa₂Cu₃Oy (RE-123) coated conductors with various plated-copper thicknesses (20 and 40 µm). A short sample of coated conductors was conduction-cooled to 45 K, a magnetic field (µ₀H, up to 2 T) was applied perpendicular to its wide face to control the critical current, an operating current was supplied, and subsequently quench was initiated using a small heater. Normal zone propagation velocities (NZPVs) were measured at various operating currents, and the NZPVs of coated conductors with various copper thicknesses were compared with each other. To understand the impact of the copper stabilizer on quench protection, hot-spot temperatures were measured during the processes that simulate quench detection using voltage taps and protection using dump resistor. The maximum hot-spot temperatures were plotted against the operating current as well as the overall current density, and the impact of the thickness of the copper stabilizer on hot-spot temperature was examined. The impact of the initial temperature on hot-spot temperature was also studied.

In the context of CERN's high-luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC), a new double aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These 2.2 m long NbTi dipoles are built with the canted cosine theta (CCT) technique. The two independently powered apertures are oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A full-length double aperture prototype was built and tested at CERN in the SM18 test facility. Here we present the results of powering tests at 1.9 and 4.5 K: training of each aperture, magnetic field quality and cross-talk effects, quench detection system effectiveness, quench protection performance and quench-back with several energy extraction systems.

We evaluated hysteresis curves and Barkhausen noise properties of the martensitic stainless steel with and without quench, and then investigated the relations between magnetic parameters and hardness based on microstructure changes. The quench introduced to reduce grain size, which relates to an increment of coercivity and Vickers hardness, a decrease in Barkhausen signal. The magnetic property changes reflect the changes in microstructures and mechanical property appeared on the quenched specimen. The obtained results contribute to aim to develop a magnetic nondestructive evaluation of residual stress appeared on the ferromagnetic steel combined with and without quench.

Flue gas quench (FGQ) at advanced combined heat and power (CHP) plays a vital role by linking flue gas (FG) cleaning and wastewater treatment. In this paper, we have performed a detailed mass balance of pollutants in the flue gas and the process water with and without FGQ at a CHP plant. The results show that the system with FGQ puts less wastewater load (about 74 tonnes/day) together with less pollutant load on the municipal wastewater treatment plant (MWWTP) than the system without FGQ. Meanwhile, it results in fewer burdens on the external water use.

For the high luminosity upgrade of the CERN large hadron collider, lower beta* quadrupole magnets based on advanced Nb3Sn conductors will be installed on each side of the ATLAS and compact muon solenoid (CMS) experiment insertion zones. As part of the technological developments needed to achieve the required field gradient of 132.6 T/m within a 150-mm aperture, short length model magnets, named MQXFS, are tested both at the CERN SM18 and Fermilab test facilities. The model magnets rely on two types of Nb3Sn conductors (restack rod process (RRP) and powderin-tube (PIT)) and on an innovative bladders and keys design to provide mechanical support against the Lorentz forces. In 2016 and 2017, the powering tests of the first two models MQXFS3 (RRP) and MQXFS5 (PIT) proved that nominal performance (16.5 kA) could be reached with excellent memory of the quench current after thermal cycle. However both magnets showed a slow training behavior with clear observations of voltage disturbances before the quench. Besides, only MQXFS5 could reach ultimate current (17.9 kA) whereas erratic behavior was observed on MQXFS3 due to conductor local degradation at the head of one of the coils. In 2018, this limiting coil was changed and the applied azimuthal prestress increased. While ultimate current could then be reached, no stable current could be maintained due to identified defect on the outer layer of the new coil. Finally the outcome of the test of the new model MQXFS4, featuring the final RRP conductors that will be used for the series production and variation on the inner layer quench heater designs are here reported in details.

In the frame of the high-luminosity upgrade project for the large hadron collider, new twin aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long canted cosine theta NbTi dipoles, with two independently powered apertures oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A 0.5 m model magnet in single and double aperture configuration and a full-length double aperture prototype were built and tested at CERN. In this paper, the performance of these magnets at 1.9 K in terms of training behavior, quench detection and protection, and other tests is discussed. In addition, the thermal response of the magnet to a hypothetical beam discharge is simulated and analyzed.

Since the reactor pressure vessel (RPV) of a typical BWR features a lower head that is penetrated by a forest of control rod guide tubes (CRGTs), coolability of the debris bed formed in the lower head during a severe accident can be realized by coolant injection through the CRGTs (so-called "CRGT cooling"). This paper is concerned with performance assessment of such CRGT cooling system, whose heat removal capacity is determined by two mechanisms: (i) heat-up and boiling of coolant inside the CRGTs; and (ii) evaporation of coolant which reached the top of the debris bed from CRGTs (top flooding). For this purpose, analyses were accomplished by coupling the COCOMO and RELAP5 codes, which simulate the quenching process of the debris bed and the coolant flow inside the CRGTs, respectively. An analysis was first carried out for a unit cell with a single CRGT, whose decay heat removal was limited by heat conduction from debris to the CRGT wall. The simulation indicated that without top flooding, though the temperature of the unit cell was eventually stabilized by the cooling of the CRGT wall, remelting of metallic debris (Zr) in the peripheral region was unavoidable due to low conductivity of corium. Boiling in the CRGT was not only beneficial to heat transfer, but also contributing to a flat axial temperature profile. Given the nominal flowrate of the CRGT cooling, the coolant was not completely boiled off in the CRGT, and therefore the remaining liquid water at the outlet of the CRGT was available for top flooding of the debris bed. The subsequent simulation including the top flooding showed that the debris bed was rapidly quenched without any remelting. However, the top flooding may have a side effect which was Zr oxidation risk at high temperature, leading to production of reaction heat and H-2. Finally analyses were performed for prototypical cases for a reference Nordic BWR, and the results implied that the CRGT cooling could be used as a promising strategy for seve, QC 20190806

High field superconducting magnets for particle accelerators often exhibit premature quenches. Once a normal zone is generated within the conductor, the quench may propagate causing temperature and resistive voltage rise along the coil. The resulting thermal gradients can potentially cause new peak stresses that might exceed the tolerable limits, degrading the conductor. The computation of the strain state in the coils during quench then becomes of paramount importance for magnet design, and requires a complete three-dimensional (3-D) analysis of quench phenomena. The objective of this paper is to present the first multiphysics modeling activities towards a new full 3-D methodology for the analysis of magnet mechanics during quench. As a first step, a 3-D thermal-electric finite element model of a Nb3Sn superconducting coil is developed and explained here. The model uses direct coupled-field elements to solve the system of thermal and electrical equations. A solving algorithm has also been implemented in order to investigate the physics behind quench transients. The output from this model, built in ANSYS APDL, can be easily coupled in a later stage to a mechanical model in order to estimate the strain state in the coil windings. A very good agreement has been observed between the numerical results and experimental tests performed in individual superconducting cables and real superconducting magnets.

The need for quenched and tempered steel increased, especially for the manufacture of the combat vehicle components. This steel is classified as high-strength and hardness and is bullet-resistant steel (armor steel). Maintaining the stability of steel hardness is very important because the quality standard for armor steel is hardness. High hardness causes brittleness increase, and tempers are needed to reduce it (residual stress is relieved by temper). Austenite temperature and temper affect steel hardness and wear resistance of quenched and tempered steel. To obtain hardness and wear due to the influence of quench and temper on hot rolled plate steel as the armor steel candidate. The material used in this research is hot rolled plate steel made in Indonesia with a carbon content of 0.29 %. The method used is heating the material to 900 °C, 885 °C and 870 °C (held for 45, 30 and 15 minutes) and cooling in water and quenched steel is produced. Quenched steel is heated to 150 °C (held for 45, 30 and 15 minutes) and cooled in atmospheric air. Optimum heat treatment parameters, the Taguchi and ANOVA methods were used. From the parameters and level of heat treatment chosen, the number of specimens needed can be known. The parameter of heat treatment has a strong influence on hardness, and ANOVA can obtain wear. Optimum hardness and wear are 566.48 HVN (±532 BHN) and 2.01×10−9 mm2/kg, respectively. Both are influenced by austenite and temper temperature., Потребность в закаленной и отпущенной стали, особенно для изготовления компонентов боевых машин, возросла. Эта сталь классифицируется как высокопрочная, твердая и пуленепробиваемая (броневая сталь). Поддержание стабильности твердости стали очень важно, так как твердость является стандартом качества для броневой стали. Высокая твердость приводит к возрастанию хрупкости, поэтому для ее уменьшения необходим отпуск (остаточное напряжение снимается отпуском). Температура аустенита и отпуска влияют на твердость и износостойкость закаленной и отпущенной стали. Твердость и износостойкость возможно получить благодаря влиянию закалки и отпуска на горячекатаную листовую сталь в качестве броневой стали. Материалом, использованным в данном исследовании является горячекатаная листовая сталь, изготовленная в Индонезии с содержанием углерода 0,29%. Используемый метод заключается в нагреве материала до 900, 885 и 870 °С (выдерживают в течение 45, 30 и 15 минут), охлаждении в воде, производится закаленная сталь. Закаленную сталь нагревают до 150 °С (выдерживают в течение 45, 30 и 15 минут) и охлаждают на атмосферном воздухе. Были использованы оптимальные параметры термообработки, методы Тагути и дисперсионный анализ. По выбранным параметрам и уровню термообработки можно узнать количество необходимых образцов. Параметр термообработки оказывает сильное влияние на твердость, а дисперсионный анализ – на износостойкость. Оптимальная твердость и износостойкость составляют 566,48 HVN (±532 BHN) и 2,01×10-9 мм2/кг соответственно. На оба влияет температура аустенита и отпуска., Потреба в гартованiй та відпущенiй сталі, особливо для виготовлення компонентів бойових машин, зросла. Ця сталь класифікується як високоміцна, тверда і куленепробивна (броньова сталь). Підтримання стабільності твердості сталі дуже важливе, адже твердість є стандартом якості для броньової сталі. Висока твердість призводить до зростання крихкості, тому для її зменшення необхідний відпуск (залишкова напруга знімається відпуском). Температура аустеніту і відпуску впливають на твердість і зносостійкість гартованої та відпущеної сталі. Твердість і зносостійкість можливо отримати завдяки впливу гартування і відпуску на гарячекатану листову сталь в якості броньової сталі. Матеріалом, використаним в даному дослідженні є гарячекатана листова сталь, виготовлена в Індонезії з вмістом вуглецю 0,29 %. Використовуваний метод полягає в нагріванні матеріалу до 900, 885 і 870 °С (витримка протягом 45, 30 і 15 хвилин), охолодженні у воді, виготовляється гартована сталь. Гартовану сталь нагрівають до 150 °С (витримують протягом 45, 30 і 15 хвилин) і охолоджують на атмосферному повітрі. Були використані оптимальні параметри термообробки, методи Тагуті і дисперсійний аналіз. За обраними параметрами і рівнем термообробки можна дізнатися кількість необхідних зразків. Параметр термообробки впливає на твердість, а дисперсійний аналіз – на зносостійкість. Оптимальна твердість і зносостійкість становлять 566,48 HVN (±532 BHN) і 2,01×10-9 мм2/кг відповідно. На обидва впливає температура аустеніту і відпуску

To control the emission of pollutants in the flue gas, a separated flue gas quench was added after flue gas desulfurization and before flue gas condensation. A mathematic model was developed to simulate the heat and mass transfer in the flue gas quench. The model was validated through the comparison with measured data. Based on this model, the impacts of inlet flue gas condition and injected recycling water flow rate on the water consumption of the quench and the temperature of exit flue gas (FG) were studied. The results show that the temperature of exit FG and water consumption increased with the increase of flow rate and moisture content of FG. The temperature of exit FG increased and the water consumption decreased with the increase of droplet water diameter. The temperature of exit FG decreased and the water consumption increased with the increase of water flow rate. In order to cooled and humidified the flue gas sufficiently, the droplet diameter should be limited to 1.2 mm and the water to FG flow rate ratio (L/G) higher than 2., QC 20190611

This paper is concerned with the coolability of the heap-like debris beds formed in the cavity of a Nordic-type boiling water reactor (BWR) during a postulated severe accident. A numerical simulation using the MEWA code was performed to investigate the quenching process of the ex-vessel debris bed at post-dryout condition upon its formation. To qualify the simulation tool, the MEWA code was first employed to calculate the quenching tests recently conducted on the PEARL facility. Comparisons of the simulation results with the experimental measurements show a satisfactory agreement. The simulation for the debris bed of the reactor scale shows that the heap-like debris bed flooded from the top is quenched in a multi-dimensional manner. The upper region adjacent to the centerline of the bed is the most difficult for water to reach under the top-flooding condition, and thus is subject to a higher risk of remelting. The oxidation of the residual Zr in the corium has a great impact on the coolability of the debris bed due to (i) large amount of reaction heat and the subsequent positive temperature feedback, (ii) the local accumulation of the produced H2 which may create a “steam starvation” condition and suppresses the oxidation. As possible mitigation measures of oxidation, the effects of bottom-flooding and bypass on quench were also investigated. It is predicted that the debris bed becomes more quenchable with water injected from the bottom, especially for the case with the floor partially flooded in the center. A bypass channel embedded in the center of the debris bed can also promote the quenching process by providing a preferential path for both steam escape and water inflow., Funding details: ENSI, Eidgenössisches Nuklearsicherheitsinspektorat; Funding details: 201409110105, CSC, China Scholarship Council; Funding details: CSC, China Scholarship Council; Funding text: This study was made possible by the support from the research programs of APRI, ENSI and NKS. The authors are grateful to the support of the China Scholarship Council (CSC, scholarship No. 201409110105). The authors acknowledge IKE of Stuttgart University for making the MEWA code available to us and providing technical supports in utilization of the codes. Special gratitude goes to Dr. Michael Buck for patient and knowledgeable guidance. QC 20181127

The high luminosity upgrade project U.S. LARP/HiLumi has successfully tested the first 1.5 m prototype quadrupole MQXFS1 at Fermilab’ Magnet test facility. Several thermal cycles and test programs were performed, with different preload configurations. To localize and characterize quenches, a quench antenna and voltage taps are used. The quench antenna was placed inside a warm bore of an anticryostat centered in the magnet. We varied the length between quench antenna segments from 2.54 to 15.24 cm, and shifted the location of the antenna to localize the quench origin along the various wedge and spacers transitions in the lead end of the magnet. We present results on the identified quench locations for the second and third thermal cycle in this paper.

The generation and propagation of quench induced by a local heat disturbance or by overcurrents in MgB2 Rutherford cables have been studied experimentally. The analysed cable is composed of 12 strands of monocore MgB2/Nb/Cu10Ni wire and has a transposition length of about 27 mm. Measurements of intra- and inter-strand voltages have been performed to analyse the superconducting-to-normal transition behaviour of these cables during quench. In case of external hot-spots, two different time-dynamic regimes have been observed, a slow stage for the formation of the minimum propagation zone (MPZ), and a fast dynamics once the quench is triggered and propagates to the rest of the cable. Significant local variations of the quench propagation velocity across the strands around the MPZ have been observed, but with average quench propagation velocities closely correlated with the predictions given by one-dimensionalgeometry models. For quench induced by overcurrents (i.e. with applied currents higher than the critical current) the nucleation of many normal zones distributed within the cable, which overlap during quench propagation, gives a distinctive and faster quench dynamics.

High-field MQXF-series quadrupoles are presently under development by LARP and CERN for the upcoming LHC luminosity upgrade. Quench training and protection studies on MQXF prototypes require a capability to accurately localize quenches and measure their propagation velocity in the magnet coils. The voltage tap technique commonly used for such purposes is not a convenient option for the 4.2-m-long MQXF-A prototype, nor can it be implemented in the production model. We have developed and tested a modular inductive magnetic antenna for quench localization. The base element of our quench antenna is a round-shaped printed circuit board containing two orthogonal pairs of flat coils integrated with low-noise preamplifiers. The elements are aligned axially and spaced equidistantly in 8-element sections using a supporting rod structure. The sections are installed in the warm bore of the magnet, and can be stacked together to adapt for the magnet length. We discuss the design, operational characteristics and preliminary qualification of the antenna. Axial quench localization capability with an accuracy of better than 2 cm has been validated during training test campaign of the MQXF-S1 quadrupole.

Quench is a widely used technique in organic synthesis or inorganic material treatment but only limited studies have been performed on aluminosilicate. In this work, the quench effect on the textural properties and surface functional groups has been studied by the functionalization of a waste-derived aluminosilicate material. The porous structure has been changed in the presence of a quench reagent. We consider that this difference originated due to the prevention of replacement of potassium atoms in surface ion-exchange sites by hydrogen atoms. Surface characterization including SEM, XPS and FTIR further confirmed the preservation of Si[sbnd]O[sbnd]K functional groups. Meanwhile, due to the differences between the electronegativities of potassium atoms and hydrogen atoms the ion-exchange ability for heavy metals of the quenched samples was significantly enhanced and this has been validated by adsorption experiments with various kinds of metals. The mass balance for leaching calcium and potassium atoms also revealed that the enhanced ion-exchange capacity was caused by the improved liberation of potassium and calcium atoms from the aluminosilicate network. Moreover, the leaching test for metal doped material shows a limited amount of metal leaching under acidic conditions, indicating the potential application of this material in industrial wastewater treatment or catalysis applications. © 2016 Elsevier B.V.

The study of the relaxation process that follows a quantum quench in 1D systems still represents an open research field. Here we consider a sudden change of the interparticle interaction and we identify a peculiar correlator of the system whose behavior is directly and deeply affected by the quench-induced dynamics. Interestingly, it features a universal power-law decay in time. Unfortunately, such a universal decay, although present, turns out to be subleading in intrinsic properties of the system such as the non- equilibrium spectral function. We thus consider a tunnel coupling of the system with a biased tip in order to be able to study also transport properties, namely the charge and energy current flowing from the tip to the system after the quench. In these quantities the universal power-law emerges clearly, especially if one focuses on energy current and its fractionalization into a right- and left- moving components. In particular, we show that the presence of a transient in the energy fractionalization ratio is a direct hallmark of the quench-induced relaxation. Within the setup we have considered, time-dependent transport properties are thus promoted to useful and promising tools to access the mechanisms at the base of the out-of- equilibrium dynamics following quantum quench.

We investigate the time evolution towards the asymptotic steady state of a one-dimensional interacting system after a quantum quench. We show that at finite times the latter induces entanglement between right- and left-moving density excitations, encoded in their cross-correlators, which vanishes in the long-time limit. This behavior results in a universal time decay ∝t−2 of the system spectral properties, in addition to nonuniversal power-law contributions typical of Luttinger liquids. Importantly, we argue that the presence of quench-induced entanglement clearly emerges in transport properties, such as charge and energy currents injected in the system from a biased probe and determines their long-time dynamics. In particular, the energy fractionalization phenomenon turns out to be a promising platform to observe the universal power-law decay ∝t−2 induced by entanglement and represents a novel way to study the corresponding relaxation mechanism.

Future high-energy physics demands higher magnetic fields to attain higher beam energies and thus needs novel superconductingmaterials in accelerator magnet applications. Current superconductors operate in the temperature range between 1.8 and 4.2 K and attain 8 T in modern operational machines. Meanwhile, prototypes have been built to operate up to 12 T, which approaches the foreseen maximum attainable practical dipole field of 16 T of modern low temperature superconductors. In the framework of the long-term European development project Eucard-2, within the work package ’Future Magnets’, the technology for dipole magnets in the 16 to 20 Tesla range is explored. High Temperature Superconductor (HTS) materials have the ability to provide these high magnetic fields, but are in an early stage of development. In the recent past, significant improvements have been achieved by increasing current density and reducing cost, which implies the conductors’ future potential. The superconducting regime stretches much higher in both temperature and flux density compared to modern Low Temperature Superconductors (LTS), offering a new range of operating regimes. Higher current densities can be reached at the same operating temperature or, equal current densities can be reached at higher temperatures. The increased operating current density reduces the required conductor volume which leads, consequently, to more compact designs, while a higher operating temperature poses less restraints on the cryogenic cooling facilities. This versatility offers great potential for future magnet applications, however complicates thermal stability. Higher current densities and larger thermal margins result in very local normal zones with high peak temperatures endangering the magnet’s integrity. Adequate protection is therefore essential for safe operation especially in high energy density applications, such as multi-strand cables in accelerator dipoles. A quench should be detected sufficiently in a, Mechanical, Maritime and Materials Engineering, Precision and Microsystems Engineering

We have proposed a new method for detecting unusual local conditions in a high-temperature superconducting coil. In this method, two kinds of pick up coils for measuring electric fields and magnetic fields are used to obtain Poynting's vectors around the coil. This is a noncontact method using pick-up coils around the vessel for cooling the coil. The method has the following benefits: safe detection, easy handling, high sensitivity, and high usability. The purpose of this paper is to clarify the relation of measured signals to the conditions of the windings. When a temperature rise has been produced locally in the Bi-2223 solenoidal coil, Poynting's vectors around the coil and the temperature of windings were measured. It was found that the measured signals rapidly decrease as the temperature of the winding achieved a critical level, making this a reliable method to estimate the conditions in the windings.

Early quench detection and thermal stability of superconducting coils are of great relevance for practical applications. Magnets made with second generation high temperature superconducting (2G-HTS) tapes present low quench propagation velocities and therefore slow voltage development and high local temperature rises, which may cause irreversible damage. Since quench propagation depends on the anisotropy of the thermal conductivity, this may be used to achieve an improvement of the thermal stability and robustness of 2G-HTS coils. On pancake type coils, the thermal conductivity along the tapes (coil's azimuthal direction) is mostly fixed by the 2G-HTS tape characteristics, so that the reduction of anisotropy relies on the improvement of the radial thermal conductivity, which depends on the used materials between superconducting tapes, as well as on the winding and impregnation processes. In this contribution, we have explored two possibilities for such anisotropy reduction: by using anodised aluminium or stainless steel tapes co-wound with the 2G-HTS tapes. For all the analysed coils, critical current distribution, minimum quench energy values and both tangential and radial quench propagation velocities at different temperatures and currents are reported and compared with the results of similar coils co-wound with polyimide (Kapton®) tapes.

We report on the spontaneous production of fluxons in annular Josephson tunnel junctions during a thermal quench in the presence of a symmetry-breaking magnetic field. The dependence on field intensity B of the probability (f) over bar (1) to trap a single defect during the N-S phase transition depends drastically on the sample circumferences. We show that this can be understood in the framework of the same picture of spontaneous defect formation that leads to the experimentally well attested scaling behavior of (f) over bar (1) with quench rate in the absence of an external field.

Document(en) uit de collectie Chemische Procestechnologie, DelftChemTech, Applied Sciences

Bakalářská práce se zabývá problematikou výskytu zbytkového austenitu u příčníku článku harvestorového kolopásu při popouštění po delší době. Zvoleným materiálem je borová ocel 27MnCrB5-2. Experiment probíhá porovnáním tří vzorků, první je popuštěn ihned po kalení, druhý 48 hodin po kalení a třetí popuštěn není. Dle předběžných výpočtů rychlostí ochlazování a teploty Mf je přítomnost zbytkového austenitu nepravděpodobná. U všech metalografických výbrusů je optickým mikroskopem pozorovatelná identická martenziticko-bainitická struktura. Na rastrovacím mikroskopu se u obou popuštěných materiálů vyskytuje dolní bainit s karbidy uvnitř feritických lamel. Pouze zakalený vzorek má obtížně rozlišitelné karbidy od martenzitické struktury, avšak bez známek zbytkového austenitu. Z výsledků měření tvrdosti má nejvyšší tvrdost zakalený příčník, a dle příslušné křivky v ARA diagramu odpovídá tvrdost bainitické struktuře. Výskyt zbytkového austenitu byl definitivně vyloučen rentgenovou difrakcí při nižším výskytu, než je 2% rozlišitelnost využitého zařízení., This bachelor thesis deals with the problem of the occurrence of residual austenite in the crossbar of a harvester forestry tracks during tempering after a longer period of time. The chosen material is boron steel 27MnCrB5-2. The experiment is carried out by comparing three samples, the first is tempered immediately after quenching, the second is tempered 48 hours after quenching and the third is not tempered. According to preliminary calculations of cooling rates and Mf temperature, the presence of residual austenite is unlikely. On all metallographic smears, an identical martensitic-bainitic structure can be observed by optical microscopy. On a scanning microscope, both tempered materials show lower bainite with carbides within the ferritic lamellae. Only the quenched sample has carbides that are difficult to distinguish from the martensitic structure, but no evidence of residual austenite. Based on the hardness measurements, the quenched crossbar has the highest hardness. According to the corresponding curve in the CCT diagram, the hardness corresponds to the bainitic structure. The occurrence of residual austenite was definitely ruled out by X-ray diffraction at less than 2% resolution of the equipment used