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Authors:
Takahiro Kawaguchi;Kazuyoshi Takagi;Naofumi Takagi;
Pages: 1 - 9 Abstract: Superconductive single-flux-quantum (SFQ) circuits operate with very high clock frequency and its timing design is a difficult task. In circuit design, static timing analysis (STA) is a key process for evaluating and verifying the timing of a circuit design. Conventional timing analysis for SFQ circuits focuses on circuits composed of clocked gates and splitters; however, practical SFQ circuits are composed of various gates, i.e., not only clocked gates but also other gates, such as nondestructive read-out, confluence buffer, and clockless logic gates. In this article, to express timing constraints of both clocked gate cells and other cells, we define timing requirements of cells as minimum and maximum acceptable intervals on ordered pairs of input pins. Via these, we express timing constraints of cells in an SFQ circuit design. Furthermore, to eliminate unnecessary pessimism during variation-aware timing analysis, we propose a method of common path pessimism removal (CPPR) for SFQ circuits composed of various cells. We implement an STA tool using the defined timing constraints and the CPPR method. The experimental results show that our STA tool verifies the timing of SFQ circuits composed of various cells. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Ching-Cheng Wang;Wai-Kei Mak;
Pages: 1 - 12 Abstract: In a single-flux-quantum (SFQ) circuit, almost all cells need to receive the clock signal which incurs a high clock routing overhead. Besides, the clock tree of an SFQ circuit requires the insertion of a clock splitter cell at every tree branching point which renders the conventional design flow of placement followed by clock tree synthesis ineffective to obtain a high quality clock tree with low clock skew. Moreover, very few works in the literature attempted to minimize the maximum path length during SFQ circuit placement. The maximum path length which is the length of the longest source-to-sink path of any data signal should be minimized to achieve higher final performance and to reduce the overhead for length matching in subsequent routing. To address these issues, we propose a two-stage global placement methodology and a placement refinement algorithm after placement legalization. Our two-stage global placement methodology first applies a conventional global placement algorithm to place the cells in the given SFQ circuit evenly, which is followed by clock tree synthesis and clock splitter insertion, and then performs a second stage of global placement to re-place both the original cells and clock splitters at the same time. In the second global placement stage, the look-ahead legalization technique is used to spread out the original cells and the clock splitters, and the clock tree is re-synthesized several times to obtain an optimized clock tree topology such that there are little overlaps of the clock splitters with the original circuit cells. We propose a novel net model in global placement that facilitates the concurrent optimization of the total wirelength and the maximum path length. After legalizing the placement of all cells, a specialized placement refinement method is run to further reduce the clock skew and the maximum path length. Compared with the previous state-of-the-art work, on average we reduced the total half-perimeter wirelength by 9%, redu-ed the maximum path length by 58%, and reduced the clock skew by 32%. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Sergey K. Tolpygo;Evan B. Golden;Terence J. Weir;Vladimir Bolkhovsky;
Pages: 1 - 31 Abstract: Data are presented on mutual and self-inductance of various inductors used in multilayered superconductor integrated circuits: microstrips and striplines with widths from 250 nm to a few micrometers, located on the same layer at various distances from each other, from 250 nm to a few micrometers, and/or on different layers spaced vertically; effect of long slits in the ground plane(s) along the inductors on their mutual inductance; inductance of right-angled bends; and inductance of meanders. Measurements were done using circuits fabricated in the SFQ5ee and the SC1 fully planarized fabrication processes with eight niobium layers and Nb/Al-AlOx/Nb Josephson junctions, developed at MIT Lincoln Laboratory for superconductor electronics. Simple analytical expressions for mutual and self-inductance of the basic inductors are given, describing experimental data with accuracy better than 2% over a very wide range of parameters. Mutual coupling between microstrips is long-ranged and decreases as a second power of distance between them, making microstrips unsuitable for very large scale integrated circuits. Mutual inductance of striplines decreases exponentially with distance between them on a scale of $({boldsymbol{H}} + 2{boldsymbol{lambda }})/{boldsymbol{pi }}$ ∼ 0.3 μm, where ${boldsymbol{H}}$ and ${boldsymbol{lambda }}$ are, respectively, the distance between and magnetic field penetration depth in superconducting ground planes, whereas superconducting properties of the signal traces are practically irrelevant. This decay distance determines the scale of integration above which adjacent induct-rs in a circuit become strongly coupled. Dependence of mutual inductance on the linewidth of wires is weak. As a result, the area of flux transformers—an essential component of all superconductor digital circuits using ac power, qubits, and sensor arrays—scales poorly with the linewidth, potentially restricting scalability of the circuits. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Bokyung Kim;Kwon-Kyu Yu;Sang-Kil Lee;Hyukchan Kwon;Jin-Mok Kim;Yong-Ho Lee;
Pages: 1 - 6 Abstract: For reliable and long-term operation of superconducting quantum interference devices (SQUIDs), proper protection against mechanical damage and electrostatic discharge is required. In this study, we developed a simple and practical molding method using a polydimethylsiloxane–carbon black composite to protect SQUIDs. By simply dipping SQUIDs into the molding composite precursor, they could be molded reliably with no additional mechanical damage from the molding process itself. Additionally, the molded SQUIDs showed no degradation in the flux–voltage modulation curves for ten thermal cycles between 4.2 K and room temperature. We also compared the electrostatic discharge immune characteristics of bare and molded SQUIDs by applying air discharge voltages in the range of 0.1–4.0 kV. Among the 52 SQUIDs with or without molding, all the molded SQUIDs survived up to 1.2 kV. For higher discharge voltages, the molded SQUIDs have a lower likelihood of damage than the bare SQUIDs. This study also confirmed that neither the molding material nor process increase the flux noise, indicating that the developed molding method can be used reliably for multichannel SQUID systems. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Yongliang Wang;
Pages: 1 - 6 Abstract: Superconducting Josephson junctions and quantum phase slip (QPS) junctions create various hybrid circuits combined with nonsuperconducting elements. Those circuits require a common analysis method to bridge the gap between superconducting and nonsuperconducting electronics. This article presents an electromagnetic-flux-distribution model to unify the analyses of superconducting and non-superconducting circuits. This model uses electric and magnetic fluxes as the variables to unify the definitions of circuit elements and circuit laws; it derives general circuit equations of the circuits viewed from both electric and magnetic fields, to depict their dynamics and duality principles. This method is demonstrated in the analyses of a Josephson junction circuit and its dual QPS junction circuit. It shows that Josephson junction circuits are the magnetic-flux distribution network tuned by the Josephson current, while QPS junction circuits are the electric-flux distribution network modulated by the QPS voltage. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Simon K. H. Lam;Keith E. Leslie;Jeina Lazar;
Pages: 1 - 4 Abstract: Rf SQUIDs have been fabricated on MgO substrate using step-edge YBCO junction. Ion beam etching as a post fabrication trimming process is routinely used to reduce (trim) the critical current of the junction for noise optimization. The white noise of SQUIDs with inductance, Ls = 157 pH can be reduced to 55 μΦoHz−1/2 after the trimming process. However, 1/f noise at low frequency has been found to be degraded after the trimming. Rf SQUIDs with Ls = 130 pH were fabricated and measured. A similar noise performance was achieved in these SQUIDs down to 5 Hz without the need of trimming. The 1/f noise was found to be better than that of the trimmed SQUIDs. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Xing Huang;Xinning Hu;Zili Zhang;Chunyan Cui;Hao Wang;Feifei Niu;Yuan Zhang;Luzhong Wang;Qiuliang Wang;
Pages: 1 - 7 Abstract: High-resolution superconducting gravimeters (SGs) require μK-level temperature control. Passive isolation can increase the risk of quenching the superconducting gravity sensing unit. Also, the use of a vacuum chamber for passive isolation increases complexity and complicates the operation of the instrument. Therefore, to investigate how to avoid using passive isolation, we developed an analytical computation model based on the Maxwell-London (ML) equations for calculating the magnetic levitation forces of the SG, taking into account the penetration depth characteristics of type II superconducting sphere. The model can be used to calculate the independent contributions of the upper and lower superconducting coils to the superconducting sphere levitation force, the magnetic gradient of the SG, and most importantly, the temperature coefficient of the SG temperature effect. Calculations show that temperature variations change the penetration depth and levitation force of the superconducting sphere and that the penetration depth determined at 4.2 K corresponds to a unique temperature coefficient, which means that the effect of the same temperature on the levitation force of the superconducting sphere is definite for a certain penetration depth. Further studies find that the temperature coefficient depends linearly on the effective penetration depth of the superconducting sphere, and the greater temperature coefficient than that of the smooth superconductor depends on the surface preparation and surface oxidation of the superconducting sphere. After discussion, it is clear that Nb coating on the surface of superconducting spheres is an effective solution to avoid passive isolation in the future. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Libin Cui;Jun Luo;Zhenhua Su;Yongzeng Li;Jin Li;Zhixuan Zhu;Guangtong Ma;
Pages: 1 - 8 Abstract: In this article, a fast design optimization of null-flux coils (NFCs) was investigated to improve the performance of electrodynamic suspension (EDS) based on response surface method (RSM) and archive-based micro genetic algorithm (AMGA). The approximate model of levitation force was established using RSM. Six geometry parameters of NFCs were selected; the mass of NFCs per kilometer and the levitation force were chosen as the optimization objectives. In order to improve the efficiency of design optimization, the comprehensive sensitivity of the selected six variables was analyzed. Hence, four size parameters were determined as the design variables. A total of 1099 Pareto points were obtained through AMGA, and the optimal design variables were selected from the Pareto front. Finally, a finite element model was established to verify the authenticity of the mathematical model, and the electromagnetic characteristics before and after optimization were compared. The results indicated that the proposed optimization method could greatly improve the performance of EDS and reduce the construction cost per kilometer. The whole optimization design cycle only needs about 43 s, and has great significance for the efficient design of EDS. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Tahereh Jabbari;Eby G. Friedman;
Pages: 1 - 6 Abstract: The increasing complexity of modern superconductive circuits, and single flux quantum (SFQ) circuits in particular has made the issue of flux trapping of growing importance. The use of wide superconductive striplines for signal routing has exacerbated this issue. Trapping residual magnetic fields in these striplines degrades performance while reducing margins, damaging the operability of superconductive circuits. In this article, an area efficient topology for striplines is introduced to manage flux trapping in large scale SFQ circuits. This topology is composed of narrow parallel lines in series with small resistors. The proposed topology decreases the length of the striplines by exploiting the mutual inductance between the narrow parallel lines. The topology requires significantly less area while preventing flux trapping within wide superconductive striplines. The narrow parallel line topology also reduces coupling capacitance between striplines. The proposed approach is compatible with automated routing of large scale SFQ integrated circuits. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Mikolaj Bednarski;Jaromir Ludwin;Damian Wojas;Mateusz Bednarek;Giorgio D’Angelo;
Pages: 1 - 7 Abstract: A fundamental component of the quench protection system of the large hadron collider (LHC) superconducting dipole magnets are bypass diodes. During a quench, the high current powering the magnet coil is redirected through the parallel diode. The resistance of diode current lead contacts is essential due to the risk of overheat. There is no possibility to measure their resistances, as the superconducting magnet coil acts as a short-circuit. Those measurements are possible when the magnet is in the resistive state. The most important point is the contact surface between the magnet busbar and the diode current lead. The resistance of this contact is not possible to measure when the cryostat is closed, so an indirect method that includes the resistance of the copper parts has to be developed. This article describes the methodology of measurements and calculations and summarizes the results of the resistance measurements of copper current leads of the LHC dipole bypass diodes. The measurements have been performed in a wide temperature region, to reproduce different environmental parameters of the LHC. It was proven that the temperature of measured samples has a significant influence on obtained results and a systematic approach is essential. Precise values of the resistance parameters have been obtained and will be used in the future measurements of the quality of connection of those diodes and, in consequence, will be used in the quality assurance of the quench protection system. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Andrea Zappatore;Roberto Bonifetto;Xabier Sarasola;Roberto Zanino;
Pages: 1 - 9 Abstract: Local defects in the manufacturing of high temperature superconducting cable-in-conduit conductors are known to be present at different stages of the conductor production. The impact of such defects on the performance of one module of the hybrid option of the EU DEMO Central Solenoid is investigated here using the H4C code. For such analysis, the modeling of each strand is needed, since the defect leads to a strong nonuniformity of the current distribution in the conductor cross section, which in turn causes temperature differences in the cross section during the propagation of a quench. The analysis allows to assess the level of damage in strand(s) before inducing a quench. In case a quench is initiated, the model is used to follow its propagation to assess the hotspot temperature. It is also observed that a quench is induced in the low temperature superconducting third layer starting from a quench initiated in the first layer, via interlayer thermal coupling. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Jungang Yang;Maoru Chi;Yuang Ji;Xingwen Wu;Jun Zheng;Shulin Liang;Hui Cao;
Pages: 1 - 24 Abstract: High temperature superconducting (HTS) maglev utilizes the magnetic flux pinning characteristics of vehicle's high temperature superconducting bulk to achieve the stable suspension. During the operation, ac losses will occur inside the HTS bulks due to the irregularity of the permanent magnetic guideway (PMG), causing the change of the temperature, which directly affects the stability of the suspension system. In this article, the magnetic-thermal-guideway coupled model of two-dimensional HTS bulks YBCO, liquid nitrogen (LN) and PMG is established by using COMSOL Multiphysics. The test track irregularity spectrum of high-speed railway is introduced and added to the PMG to simulate the magnetic field fluctuation caused by its arrangement irregularity. The characteristics of the HTS bulks’ power loss, the average current density distribution over the cross section and the temperature rise of the bulk, LN, and suspension gap (SG) are studied respectively under four conditions of excitations: lateral coupled with vertical excitations, lateral excitations, vertical excitations, and nonexcitations. Meanwhile, by comparing and analyzing with the model without considering the temperature, the influence of the temperature on the current density is studied. These results provide certain references for the safe and stable operation of HTS suspension system. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Masaru Tomita;Yusuke Fukumoto;Kenji Suzuki;Atsushi Ishihara;Keiji Ogose;Tomoyuki Akasaka;Yusuke Kobayashi;Taiki Onji;
Pages: 1 - 5 Abstract: To introduce the superconducting feeder cable for commercial operation of a railway system, it is required to establish technologies for safety and reliability. The behavior of the superconducting cable must be determined for the case in which the superconducting cable fails in the feeder system for railways. The superconducting cable can be introduced so that it is installed along with the existing feeder cable or so that only the superconducting cable is installed to be used as the feeder line. For this time, at first only, the superconducting cable was used to establish a circuit for feeder to the electric railcar without using the existing feeder circuit to conduct the power-transmission test and current breaking test. Then, the superconducting cable was installed along the existing feeder line to establish a circuit that is capable of feeder via both feeder lines to conduct the same tests. In both tests, it is confirmed that no problem occurs in the train and the superconducting cable system when it encounters the current breaking. For the parallel feeder system, it is found that the current path is transferred to the existing feeder line and the system is continuously capable of operating the train stably when the current is broken in the superconducting cable. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Dora Veres;Tamas Vaszary;Elena Benedetto;Daniel Barna;
Pages: 1 - 14 Abstract: While the required coil geometry for a specified transverse field pattern of straight canted-cosine-theta (CCT) magnets is well known, the same geometry—after the application of a bending transformation—would introduce unwanted field components in a magnet with a strong curvature. In this article, we introduce a coherent framework to define the field quality in curved magnets, and to construct the required 3-D winding geometry of CCT coils, without finite-element software. The method is applicable in general for any magnet configuration where the effective longitudinal current density distribution in the transverse plane can be related to the winding geometry in a unique way. The method is demonstrated on CCT magnet models being developed for the Heavy Ion Therapy Research Integration Plus European H2020 project. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Zhaofei Jiang;Donghui Jiang;Xiangyang Wu;Wenge Chen;Guangli Kuang;
Pages: 1 - 14 Abstract: In recent years, the no-insulation REBa2Cu3O7−x (REBCO) (NI-REBCO) coils with self-protecting ability show remarkable attraction and potential in high magnetic field areas. As the study develops in-depth, it is widely recognized that the uneven stress/strain generated by screening current is a crucial concern for the NI-REBCO coils operating performance, especially for NI-REBCO insert coils under high background field. Therefore, effectively reducing screening-current-induced stress/strain (SCIS) is critical for NI-REBCO coils/magnet mechanical design and steady operation. In this article, we developed a new two-dimensional numerical model to analyze the mechanical responses caused by screening current in NI-REBCO coils using the T-A multiscale model for electromagnetic behavior and discrete contact model for stress/strain analysis. After verifying the model by comparing with previous experimental data, the effectiveness of three already-reported and potential methods of mitigating SCIS [i.e., 1) combining suitable winding tension and overband support in the fabrication of coils, 2) employing multifilamentary REBCO tape suppressing screening current, and 3) co-wound metal tape strengthening stiffness of coils] is revealed by comparing the strain/stress distribution with a designed benchmark NI-REBCO coils. Furthermore, by a parametric study of the aforementioned mitigating SCIS methods, a couple of novel conclusions were found. 1) The effect of overband support on reducing SCIS gradually weakens from the outer turn to the inner turn, and the SCIS decreases gradually as the overband metal tape thickness increases, whereas there is a critical value that the SCIS would no longer significantly decreases once exceeds it. 2) The more multifilaments in REBCO tape there are, the better the effect of m-tigating SCIS. 3) The SCIS in NI-REBCO coils shows a clear decreasing trend with the increase of co-wound metal tape thickness, but the trend is gradually flattened. Finally, we summarized some feasible suggestions for the mechanical design of NI-REBCO coils to mitigate the SCIS. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
$T$
-$A$
+Formulation:+How+to+Handle+Different+Coupling+Scenarios&rft.title=IEEE+Transactions+on+Applied+Superconductivity&rft.issn=1051-8223&rft.date=2022&rft.volume=32&rft.spage=1&rft.epage=4&rft.aulast=Grilli;&rft.aufirst=Bárbara&rft.au=Bárbara+Maria+Oliveira+Santos;Gabriel+dos+Santos;Frédéric+Sirois;Roberto+Brambilla;Rubens+de+Andrade+Junior;Felipe+Sass;Guilherme+Gonçalves+Sotelo;Francesco+Grilli;">2-D Modeling of HTS Coils With $T$
-
$A$ Formulation: How to Handle Different Coupling Scenarios
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Authors:
Bárbara Maria Oliveira Santos;Gabriel dos Santos;Frédéric Sirois;Roberto Brambilla;Rubens de Andrade Junior;Felipe Sass;Guilherme Gonçalves Sotelo;Francesco Grilli;
Pages: 1 - 4 Abstract: Numerical models based on the finite-element method are popular tools for investigating the macroscopic electromagnetic behavior of high-temperature superconductor (HTS) applications. This article explains how to use the $T$-$A$ formulation in COMSOL Multiphysics for modeling HTS coils in 2-D with different coupling scenarios between the turns. First we consider a racetrack coil wound from one piece of superconducting tape. Then, we consider a coil obtained by winding a cable composed of different HTS tapes. In the latter case, the tape turns are either electrically connected along their entire length or just at the two ends of the coil: in the model, these two different types of electrical connection are implemented with the help of the electrical circuit module. The current density distributions and the ac losses of the coils in the different coupling scenarios are compared and discussed. The limits of applicability of the presented approach are pointed out. The model is developed for the straight section of racetrack coils, but can be easily adapted to axisymmetric geometries. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
João F. P. Fernandes;Vitor Maló Machado;
Pages: 1 - 11 Abstract: In this article, a two-dimensional hybrid finite-element formulation is proposed to further reduce the computational time required for the time simulation of superconducting (SC) bulks. Low computational time formulations are important for the design stage of electrical machines with superconductors, where optimization tools are typically used. The proposed hybrid formulation is based on the partitioned E-H electromagnetic scheme (EHS) formulation and the magnetic vector potential formulation (A-formulation). The EHS formulation is used to solve the domains with highly nonlinear electric materials, while the A-formulation is used to solve the nonelectric domains. The main characteristics of the EHS are its partitioned formulation, where the matrix form of Ampère's and Faraday's laws is separated and computed a priori, and the electric resistivity is defined at each node. The EHS formulation is first compared with the H-formulation for a single SC domain and then integrated with an A-formulation and compared with the H and H-φ formulations to simulate a bulk surrounded by air. Results verify the excellent accuracy of the EHS and A-EHS formulations, and a promising reduction of computational time is observed, with more emphasis on low levels of magnetization of the SC sample. When compared with the H-φ formulation, a time reduction between 48% (6 T) and 90% (1 T) is obtained. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Yi-Feng Wang;Zhao-Fei Jiang;Zhao-Xia Zhang;Xiao-Fan Gou;
Pages: 1 - 8 Abstract: High-temperaturesuperconducting Bi2Sr2CaCu2Ox (Bi2212) round wires (RWs) are multicomponent composite structure withsuperconductor Bi2Sr2CaCu2Ox as the fiber core, metallic silver (Ag) as the matrix, and a silver-magnesium alloy sheath (Ag-Mg) wrapped on the outside. The microstructure of Bi2212 RWs is found to be extremely complicated due to complex preparation process, which mainly manifested in irregular Bi2212/Ag interfaces and porous structure of Bi2212 filaments. For such Bi2212 multifilament RWs, many studies reported applied strain causing degradation of the critical current (${I_c})$, but only a few focused on exploring the mechanism of strain dependence of the ${I_c}$ degradation during a larger strain range spanning from compressive to tensile one. Based on our previous work of modeling the ${I_c}$ degradation under applied tensile strain, in this work, we tried to further interpret why applied compressive strain makes the ${I_c}$ of Bi2212 RWs drop rapidly. By using the numerical model on fully taking account of irregular Bi2212/Ag interfaces, we found that buckling deformation of Bi2212 wires, even smaller, arises after heat treatment. And, for a Bi2212 composite RW with thermal residual strain accumulation, under applied compressive strain, the results indicate that the reason of the critical current degradation is essentially tensile failure of Bi2212 filaments, which results from buckling deformation of the whole wire. Furthermore, on the current shunt model we proposed previously- the relation curve of the ${I_c}/{I_{c0}}$ versus applied compressive strain was obtained, which is well-agree with experimental data. And on these results, electromechanical analysis revealed that this relation of ${I_c}/{I_{c0}}$versus applied compressive strain results both from tensile damage of Bi2212 filaments, and subsequently current flowing cross the Bi2212/Ag interface and into Ag matrix near cracks inside filaments. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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Authors:
Joshua T. West;Arthur Kurlej;Alex Wynn;Chad Rogers;Mark A. Gouker;Sergey K. Tolpygo;
Pages: 1 - 12 Abstract: Using a fully automated cryogenic wafer prober, we measured superconductor fabrication process control monitors and simple integrated circuits on 200-mm wafers at 4.4 K, including SQIF-based magnetic field sensors, SQUID-based circuits for measuring inductors, Nb/Al-AlOx/Nb Josephson junctions, test structures for measuring critical current of superconducting wires and vias, resistors, etc., to demonstrate the feasibility of using the system for characterizing niobium superconducting devices and integrated circuits on a wafer scale. Data on the wafer-scale distributions of the residual magnetic field, junction tunnel resistance, energy gap, inductance of multiple Nb layers, and critical currents of interlayer vias are presented. A comparison with existing models is made. The wafers were fabricated in the SFQ5ee process, the fully planarized process with eight niobium layers and a layer of kinetic inductors, developed for superconductor electronics at MIT Lincoln Laboratory, Lexington, MA, USA. The cryogenic wafer prober was developed at HPD/FormFactor, Inc., Boulder, CO, USA. PubDate:
Aug. 2022
Issue No:Vol. 32, No. 5 (2022)
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