Pub Date : 2025-12-17DOI: 10.1109/TASC.2025.3644708
{"title":"2025 Index IEEE Transactions on Applied Superconductivity","authors":"","doi":"10.1109/TASC.2025.3644708","DOIUrl":"https://doi.org/10.1109/TASC.2025.3644708","url":null,"abstract":"","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"35 9","pages":"1-174"},"PeriodicalIF":1.8,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11303079","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-17DOI: 10.1109/TASC.2025.3645313
Kun Liu;Wei Zhou;Zhihua Zhang;Siyuan Liang;Shaopeng Wu;Daoyu Hu
The superconducting electrodynamic suspension (EDS) is one of the most promising technologies for developing an ultrahigh-speed maglev due to its special advantages. The superconducting coil (SC), which generates the force source for the EDS, is one of the key components. Improving the SC supporting characteristics, such as stiffness and damping, is an unavoidable challenge for enhancing the reliability and durability of the SC under long-term operation. Therefore, this article establishes a 3-D transient dynamic finite element model (FEM) to investigate the SC supporting characteristics. In this model, the frictional heat generation between the SC and the coil box is considered. First, the modeling method is verified by the one-degree-of-freedom (ODOF) vibration system, incorporating damping and friction. Second, the time-varying loads of suspension, guidance, and drag of 600 km/h are calculated based on dynamic-circuit theory and the virtual displacement method, and the stiffness of a self-developed SC support structure is tested. Third, based on the validated modeling method, the calculated time-varying loads, and the tested stiffness, the 3-D FEM of the SC is established. The dynamic response of the SC is estimated by the 3-D model, further, the support stiffness and damping are optimized. Finally, the influence of the friction coefficient on the frictional energy between the SC and coil box is investigated.
{"title":"The Influence of Supporting-Stiffness and Damping on the Superconducting Coil Dynamical Characteristics and Frictional Heat Generation in Ultrahigh-Speed EDS Maglev","authors":"Kun Liu;Wei Zhou;Zhihua Zhang;Siyuan Liang;Shaopeng Wu;Daoyu Hu","doi":"10.1109/TASC.2025.3645313","DOIUrl":"https://doi.org/10.1109/TASC.2025.3645313","url":null,"abstract":"The superconducting electrodynamic suspension (EDS) is one of the most promising technologies for developing an ultrahigh-speed maglev due to its special advantages. The superconducting coil (SC), which generates the force source for the EDS, is one of the key components. Improving the SC supporting characteristics, such as stiffness and damping, is an unavoidable challenge for enhancing the reliability and durability of the SC under long-term operation. Therefore, this article establishes a 3-D transient dynamic finite element model (FEM) to investigate the SC supporting characteristics. In this model, the frictional heat generation between the SC and the coil box is considered. First, the modeling method is verified by the one-degree-of-freedom (ODOF) vibration system, incorporating damping and friction. Second, the time-varying loads of suspension, guidance, and drag of 600 km/h are calculated based on dynamic-circuit theory and the virtual displacement method, and the stiffness of a self-developed SC support structure is tested. Third, based on the validated modeling method, the calculated time-varying loads, and the tested stiffness, the 3-D FEM of the SC is established. The dynamic response of the SC is estimated by the 3-D model, further, the support stiffness and damping are optimized. Finally, the influence of the friction coefficient on the frictional energy between the SC and coil box is investigated.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 2","pages":"1-9"},"PeriodicalIF":1.8,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-15DOI: 10.1109/TASC.2025.3644656
Jiaqi Li;Anpeng Shu;Yikai Zhang;Chenyang Han;Zhouxun Li;Yuanlong Ding;Yan Li;Yinshun Wang;Wei Pi
The high-temperature superconducting (HTS) flux pump is a charging device that can achieve contactless excitation and pro-vide stable current compensation for superconducting magnets without increasing the refrigeration burden of the system. Com-pared with the traditional excitation method through current leads, the HTS flux pump has the advantages of high safety per-formance, high excitation efficiency, and high stability, making it an effective solution for the stable operation of superconducting magnets. This article provides a detailed analysis of the working principle of the transformer-rectifier HTS flux pump based on dynamic resistance. A finite element simulation model of the su-perconducting bridge is established and a formula for calculating the dynamic resistance is obtained. Also, a measurement system for the dynamic resistance of a single superconducting tape under a composite magnetic field is constructed. Subsequently, a circuit model of the transformer-rectifier HTS flux pump is built in MATLAB Simulink and the output characteristics of the flux pump are analyzed. The results indicate that the excitation speed of the load magnet and the final saturation current are mainly affected by the amplitude, frequency, phase difference of the composite magnetic field, and the magnitude of the charging cur-rent, but are independent of the frequency of the charging cur-rent. The study also shows that the output efficiency of the flux pump peaks with a 60° phase difference of the parallel field com-ponent over the perpendicular field.
{"title":"Study on the Output Characteristics of the Transformer-Rectifier HTS Flux Pump Based on Dynamic Resistance","authors":"Jiaqi Li;Anpeng Shu;Yikai Zhang;Chenyang Han;Zhouxun Li;Yuanlong Ding;Yan Li;Yinshun Wang;Wei Pi","doi":"10.1109/TASC.2025.3644656","DOIUrl":"https://doi.org/10.1109/TASC.2025.3644656","url":null,"abstract":"The high-temperature superconducting (HTS) flux pump is a charging device that can achieve contactless excitation and pro-vide stable current compensation for superconducting magnets without increasing the refrigeration burden of the system. Com-pared with the traditional excitation method through current leads, the HTS flux pump has the advantages of high safety per-formance, high excitation efficiency, and high stability, making it an effective solution for the stable operation of superconducting magnets. This article provides a detailed analysis of the working principle of the transformer-rectifier HTS flux pump based on dynamic resistance. A finite element simulation model of the su-perconducting bridge is established and a formula for calculating the dynamic resistance is obtained. Also, a measurement system for the dynamic resistance of a single superconducting tape under a composite magnetic field is constructed. Subsequently, a circuit model of the transformer-rectifier HTS flux pump is built in MATLAB Simulink and the output characteristics of the flux pump are analyzed. The results indicate that the excitation speed of the load magnet and the final saturation current are mainly affected by the amplitude, frequency, phase difference of the composite magnetic field, and the magnitude of the charging cur-rent, but are independent of the frequency of the charging cur-rent. The study also shows that the output efficiency of the flux pump peaks with a 60° phase difference of the parallel field com-ponent over the perpendicular field.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 2","pages":"1-14"},"PeriodicalIF":1.8,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145886574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-15DOI: 10.1109/TASC.2025.3644143
Max Pröpper;Marc-André Tucholke;Dominik Hanisch;Christoph Schmid;Paul Julius Ritter;Marius Neumann;Edward Goldobin;Dieter Koelle;Reinhold Kleiner;Meinhard Schilling;Benedikt Hampel
Fabrication of YBa2Cu3O7-x Josephson junctions (JJs) using a direct-write helium-focused helium ion beam (He-FIB) technique has great potential for various applications due to tunable JJ parameters and arbitrary positioning. This technique allows placing multiple JJs in series to create JJ arrays. They could be used as a voltage standard that is operated at higher temperatures and driving frequencies than the currently used niobium-based JJ arrays. Small YBa2Cu3O7-x He-FIB JJ arrays with superposed Shapiro steps for up to three JJs have already been demonstrated. The number of JJs in the array was limited by the parameter spread of the individual JJs. This study presents WRspice simulations of JJ arrays, which indicate that the normal state resistance $R$n is the most crucial parameter to achieve flat Shapiro steps in JJ arrays. The idea of adding a shunt resistor to the JJ array to deal with the spread in $R$n values is investigated. A new design for GHz frequencies is presented, and the fabrication process is described. The properties of the shunt resistor are evaluated by van der Pauw measurements. Comparison of measurements with and without shunt resistor shows the desired effect of changing the total resistance of the JJ array while maintaining the critical current value. Finally, measurements of JJ arrays demonstrating superposed Shapiro steps at 20 k at GHz frequencies are presented.
{"title":"Shunting YBa2Cu3O7-x Josephson Junctions and Arrays Fabricated by He-FIB","authors":"Max Pröpper;Marc-André Tucholke;Dominik Hanisch;Christoph Schmid;Paul Julius Ritter;Marius Neumann;Edward Goldobin;Dieter Koelle;Reinhold Kleiner;Meinhard Schilling;Benedikt Hampel","doi":"10.1109/TASC.2025.3644143","DOIUrl":"https://doi.org/10.1109/TASC.2025.3644143","url":null,"abstract":"Fabrication of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> Josephson junctions (JJs) using a direct-write helium-focused helium ion beam (He-FIB) technique has great potential for various applications due to tunable JJ parameters and arbitrary positioning. This technique allows placing multiple JJs in series to create JJ arrays. They could be used as a voltage standard that is operated at higher temperatures and driving frequencies than the currently used niobium-based JJ arrays. Small YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> He-FIB JJ arrays with superposed Shapiro steps for up to three JJs have already been demonstrated. The number of JJs in the array was limited by the parameter spread of the individual JJs. This study presents WRspice simulations of JJ arrays, which indicate that the normal state resistance <inline-formula><tex-math>$R$</tex-math></inline-formula><sub>n</sub> is the most crucial parameter to achieve flat Shapiro steps in JJ arrays. The idea of adding a shunt resistor to the JJ array to deal with the spread in <inline-formula><tex-math>$R$</tex-math></inline-formula><sub>n</sub> values is investigated. A new design for GHz frequencies is presented, and the fabrication process is described. The properties of the shunt resistor are evaluated by van der Pauw measurements. Comparison of measurements with and without shunt resistor shows the desired effect of changing the total resistance of the JJ array while maintaining the critical current value. Finally, measurements of JJ arrays demonstrating superposed Shapiro steps at 20 k at GHz frequencies are presented.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 4","pages":"1-6"},"PeriodicalIF":1.8,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146026625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-12DOI: 10.1109/TASC.2025.3643834
Ziqi Song;Bangzhu Wang;Qihuan Dong;Tao Ma;Shaotao Dai
This article proposes a hybrid optimization method that combines linear programming (LP), differential evolution (DE) algorithm, and nonlinear programming (NLP) for the design of high homogeneity superconducting magnets in magnetic resonance imaging (MRI). To address the optimization difficulty caused by the high sensitivity of NLP to initial values, this method represents the first effort to employ the DE algorithm which serves as a bridge between LP and NLP to provide reliable initial values for NLP. The feasibility of the proposed hybrid optimization method is verified through an optimization of actively shielded MRI coils with a central magnetic flux density of 1.5 T. Finally, by comparing the optimization performance of the DE algorithm and the traditional genetic algorithm in this design, the DE algorithm is demonstrated to yield better and more stable optimization results. This hybrid optimization method provides a more efficient and reliable optimization strategy for the optimal design of MRI superconducting magnet coils.
{"title":"Optimizing High Homogeneity MRI Superconducting Magnets With a LP-DE-NLP Hybrid Method","authors":"Ziqi Song;Bangzhu Wang;Qihuan Dong;Tao Ma;Shaotao Dai","doi":"10.1109/TASC.2025.3643834","DOIUrl":"https://doi.org/10.1109/TASC.2025.3643834","url":null,"abstract":"This article proposes a hybrid optimization method that combines linear programming (LP), differential evolution (DE) algorithm, and nonlinear programming (NLP) for the design of high homogeneity superconducting magnets in magnetic resonance imaging (MRI). To address the optimization difficulty caused by the high sensitivity of NLP to initial values, this method represents the first effort to employ the DE algorithm which serves as a bridge between LP and NLP to provide reliable initial values for NLP. The feasibility of the proposed hybrid optimization method is verified through an optimization of actively shielded MRI coils with a central magnetic flux density of 1.5 T. Finally, by comparing the optimization performance of the DE algorithm and the traditional genetic algorithm in this design, the DE algorithm is demonstrated to yield better and more stable optimization results. This hybrid optimization method provides a more efficient and reliable optimization strategy for the optimal design of MRI superconducting magnet coils.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 2","pages":"1-8"},"PeriodicalIF":1.8,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fermilab is upgrading its Booster synchrotron to increase ramp rate and intensity. This is part of the Proton Improvement Plan (PIP-II) that will allow the Main Injector to achieve proton beam power of 1.2 MW within the next few years. This upgrade includes running the 55-year-old Booster magnets at 20 Hz instead of the usual 15 Hz, and construction of some shorter and wider aperture versions of these combined-function gradient magnets. Magnetic measurements were performed to characterize the present 15 Hz AC performance, and then again with 20 Hz ramp cycle to ensure performance and compatibility in this new operating regime. A 3 m-long curved flat-coil was developed for these measurements using Printed Circuit Board (PCB) technology. The probe also has a separate 0.5 m-long body-field probe, allowing integral, body, and end fields to be measured across 100 mm of the magnet aperture. The sampling rate for these measurements during the AC cycle was 200 kHz, and field resolution was better than 0.01%. Details of the probe, measurements, and results are presented.
{"title":"Magnetic Measurements of Fermilab Rapid-Cycling Booster Gradient Magnets","authors":"J. DiMarco;D. Assell;T. Cummings;D. Eddy;D. Johnson;V. Kashikhin;M. Kifarkis;J. Kuharik;J. Larson;M. Mubarak;S. Poopathi;K. Triplett","doi":"10.1109/TASC.2025.3643818","DOIUrl":"https://doi.org/10.1109/TASC.2025.3643818","url":null,"abstract":"Fermilab is upgrading its Booster synchrotron to increase ramp rate and intensity. This is part of the Proton Improvement Plan (PIP-II) that will allow the Main Injector to achieve proton beam power of 1.2 MW within the next few years. This upgrade includes running the 55-year-old Booster magnets at 20 Hz instead of the usual 15 Hz, and construction of some shorter and wider aperture versions of these combined-function gradient magnets. Magnetic measurements were performed to characterize the present 15 Hz AC performance, and then again with 20 Hz ramp cycle to ensure performance and compatibility in this new operating regime. A 3 m-long curved flat-coil was developed for these measurements using Printed Circuit Board (PCB) technology. The probe also has a separate 0.5 m-long body-field probe, allowing integral, body, and end fields to be measured across 100 mm of the magnet aperture. The sampling rate for these measurements during the AC cycle was 200 kHz, and field resolution was better than 0.01%. Details of the probe, measurements, and results are presented.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 3","pages":"1-5"},"PeriodicalIF":1.8,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145830818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-10DOI: 10.1109/TASC.2025.3642326
Wei Pi;Junhao Liang;Yan Li;Yixiang Wu;Heng Zhang;Yinshun Wang
As the development of superconducting materials reaches the bottleneck, it is worth exploring new method to obtain superconducting tapes with better performance through the composite method. In this article, BSCCO tape and REBCO tape are composited. The current distribution of the hybrid superconducting tape is investigated based on the percolation flow model, and the corresponding experiments are also carried out. The current transfer process of the hybrid superconducting tape is also simulated with the change of current and temperature. The results show that the hybrid superconducting tape has a wider temperature range and can still carry large current above the temperature of 100 K.
{"title":"Current Distribution in BSCCO/REBCO Hybrid Superconducting Tape Based on Percolation Flow Model","authors":"Wei Pi;Junhao Liang;Yan Li;Yixiang Wu;Heng Zhang;Yinshun Wang","doi":"10.1109/TASC.2025.3642326","DOIUrl":"https://doi.org/10.1109/TASC.2025.3642326","url":null,"abstract":"As the development of superconducting materials reaches the bottleneck, it is worth exploring new method to obtain superconducting tapes with better performance through the composite method. In this article, BSCCO tape and REBCO tape are composited. The current distribution of the hybrid superconducting tape is investigated based on the percolation flow model, and the corresponding experiments are also carried out. The current transfer process of the hybrid superconducting tape is also simulated with the change of current and temperature. The results show that the hybrid superconducting tape has a wider temperature range and can still carry large current above the temperature of 100 K.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 2","pages":"1-6"},"PeriodicalIF":1.8,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145802377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1109/TASC.2025.3641864
Sergey K. Tolpygo;Ravi Rastogi;David Kim;Terence J. Weir;Neel Parmar;Evan B. Golden
Increasing integration scale of superconductor electronics requires employing kinetic inductors and self-shunted Josephson junctions (JJs) for miniaturizing inductors and JJs. We have been developing a ten-superconductor-layer planarized fabrication process with NbN kinetic inductors and searching for suitable self-shunted JJs to potentially replace high Josephson critical current density, Jc, Nb/Al-AlOx/Nb junctions. We report on the fabrication and electrical properties of NbN/NbNx/NbN junctions produced by reactive sputtering in Ar+N2 mixture on 200-mm wafers at 200 °C and incorporated into a planarized process with two Nb ground planes and NbN wiring layer. Here, NbN is a stoichiometric nitride with superconducting critical temperature Tc = 15 K, and NbNx is a high resistivity nonsuperconducting nitride deposited using a higher nitrogen partial pressure than for the NbN electrodes. For comparison, we co-fabricated Nb/NbNx/Nb JJs using the same NbNx barriers deposited at 20 °C. We varied the NbNx barrier thickness from 5 to 20 nm, resulting in the range of Jc from about 1 mA/µm2 down to ∼10 µA/µm2, and extracted coherence length of 3 and 4 nm in NbNx deposited, respectively, at 20 and 200 °C. Both types of JJs are well described by the resistively and capacitively shunted junction model without any excess current. We found the Jc of NbN/NbNx/NbN JJs to be somewhat lower than that of Nb/NbNx/Nb JJs with the same barrier thickness, despite a much higher Tc and energy gap of NbN than of Nb electrodes. IcRn products up to ∼ 0.5 mV were obtained for JJs with Jc ∼ 0.6 mA/µm2. Jc(T) dependences have been measured.
{"title":"Fabrication and Properties of NbN/NbNx/NbN and Nb/NbNx/Nb Josephson Junctions","authors":"Sergey K. Tolpygo;Ravi Rastogi;David Kim;Terence J. Weir;Neel Parmar;Evan B. Golden","doi":"10.1109/TASC.2025.3641864","DOIUrl":"https://doi.org/10.1109/TASC.2025.3641864","url":null,"abstract":"Increasing integration scale of superconductor electronics requires employing kinetic inductors and self-shunted Josephson junctions (JJs) for miniaturizing inductors and JJs. We have been developing a ten-superconductor-layer planarized fabrication process with NbN kinetic inductors and searching for suitable self-shunted JJs to potentially replace high Josephson critical current density, <italic>J</i><sub>c</sub>, Nb/Al-AlO<italic><sub>x</sub></i>/Nb junctions. We report on the fabrication and electrical properties of NbN/NbN<italic><sub>x</sub></i>/NbN junctions produced by reactive sputtering in Ar+N<sub>2</sub> mixture on 200-mm wafers at 200 °C and incorporated into a planarized process with two Nb ground planes and NbN wiring layer. Here, NbN is a stoichiometric nitride with superconducting critical temperature <italic>T<sub>c</sub></i> = 15 K, and NbN<italic><sub>x</sub></i> is a high resistivity nonsuperconducting nitride deposited using a higher nitrogen partial pressure than for the NbN electrodes. For comparison, we co-fabricated Nb/NbN<italic><sub>x</sub></i>/Nb JJs using the same NbN<italic><sub>x</sub></i> barriers deposited at 20 °C. We varied the NbN<italic><sub>x</sub></i> barrier thickness from 5 to 20 nm, resulting in the range of <italic>J</i><sub>c</sub> from about 1 mA/µm<sup>2</sup> down to ∼10 µA/µm<sup>2</sup>, and extracted coherence length of 3 and 4 nm in NbN<italic><sub>x</sub></i> deposited, respectively, at 20 and 200 °C. Both types of JJs are well described by the resistively and capacitively shunted junction model without any excess current. We found the <italic>J</i><sub>c</sub> of NbN/NbN<italic><sub>x</sub></i>/NbN JJs to be somewhat lower than that of Nb/NbN<italic><sub>x</sub></i>/Nb JJs with the same barrier thickness, despite a much higher <italic>T</i><sub>c</sub> and energy gap of NbN than of Nb electrodes. <italic>I</i><sub>c</sub><italic>R</i><sub>n</sub> products up to ∼ 0.5 mV were obtained for JJs with <italic>J</i><sub>c</sub> ∼ 0.6 mA/µm<sup>2</sup>. <italic>J</i><sub>c</sub>(<italic>T</i>) dependences have been measured.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 4","pages":"1-6"},"PeriodicalIF":1.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146026626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-05DOI: 10.1109/TASC.2025.3639528
Jason Walter;Adam C. Weis;Kan-Ting Tsai;Meng-Ju Yu;Naveen Katam;Alex F. Kirichenko;Oleg A. Mukhanov;Shu-Jen Han;Igor V. Vernik
As quantum computing processors increase in size, there is growing interest in developing cryogenic electronics to overcome significant challenges to system scaling. Single flux-quantum (SFQ) circuits offer a promising alternative to remote, bulky, and power-hungry room temperature electronics. To meet the need for digital qubit control, readout, and co-processing, SFQ circuits must be adapted to operate at millikelvin temperatures near quantum processors. SEEQC's SFQuClass digital quantum management approach proximally places energy-efficient SFQ (ERSFQ) circuits and qubits in a multi-chip module. This enables extremely low power dissipation, compatible with a typical dilution cryostat's limited cooling power, while maintaining high processing speed and low error rates. We report on systematic testing from 4 K to 10 mK of a comprehensive set of ERSFQ cells, as well as more complex circuits such as programmable counters and demultiplexers used in digital qubit control. We compare the operating margins and error rates of these circuits and find that, at millikelvin, bias margins decrease and the center of the margins (i.e., the optimal bias current value) increases by ∼15%, compared to 4.2 K. The margins can be restored by thermal annealing by reducing Josephson junction (JJ) critical current Ic. To provide guidance for how circuit parameters vary from 4.2 K to millikelvin, relevant analog process control monitors (PCMs) were tested in the temperature range of interest. The measured JJ critical current (of the PCM JJ arrays) increases by ∼15% when decreasing temperature from 4.2 K to millikelvin, in good agreement with both theory and the empirically measured change in the center of bias margins for the tested digital circuits.
{"title":"Single Flux Quantum Circuit Operation at Millikelvin Temperatures","authors":"Jason Walter;Adam C. Weis;Kan-Ting Tsai;Meng-Ju Yu;Naveen Katam;Alex F. Kirichenko;Oleg A. Mukhanov;Shu-Jen Han;Igor V. Vernik","doi":"10.1109/TASC.2025.3639528","DOIUrl":"https://doi.org/10.1109/TASC.2025.3639528","url":null,"abstract":"As quantum computing processors increase in size, there is growing interest in developing cryogenic electronics to overcome significant challenges to system scaling. Single flux-quantum (SFQ) circuits offer a promising alternative to remote, bulky, and power-hungry room temperature electronics. To meet the need for digital qubit control, readout, and co-processing, SFQ circuits must be adapted to operate at millikelvin temperatures near quantum processors. SEEQC's SFQuClass digital quantum management approach proximally places energy-efficient SFQ (ERSFQ) circuits and qubits in a multi-chip module. This enables extremely low power dissipation, compatible with a typical dilution cryostat's limited cooling power, while maintaining high processing speed and low error rates. We report on systematic testing from 4 K to 10 mK of a comprehensive set of ERSFQ cells, as well as more complex circuits such as programmable counters and demultiplexers used in digital qubit control. We compare the operating margins and error rates of these circuits and find that, at millikelvin, bias margins decrease and the center of the margins (i.e., the optimal bias current value) increases by ∼15%, compared to 4.2 K. The margins can be restored by thermal annealing by reducing Josephson junction (JJ) critical current <italic>I<sub>c</sub></i>. To provide guidance for how circuit parameters vary from 4.2 K to millikelvin, relevant analog process control monitors (PCMs) were tested in the temperature range of interest. The measured JJ critical current (of the PCM JJ arrays) increases by ∼15% when decreasing temperature from 4.2 K to millikelvin, in good agreement with both theory and the empirically measured change in the center of bias margins for the tested digital circuits.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 5","pages":"1-6"},"PeriodicalIF":1.8,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145766207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-05DOI: 10.1109/TASC.2025.3639017
Heonhwan Kim;Sinhye Na;Yangjin Jung;Youngkyoung Kim;Seongtaek You;Sanghyeun Je
Large-scale scientific facilities such as fusion reactors and particle accelerators increasingly require high-performance Low-Temperature Superconducting (LTS) wires with enhanced thermo-magnetic stability. Reducing sub-element size has been shown to effectively suppress magnetization losses and improve low-field stability. Building on our earlier development of Distributed Barrier Strand (DBS) wires, which incorporate individual diffusion barriers to enhance thermo-magnetic stability, Kiswire Advanced Technology Co., Ltd. (KAT) refined the DBS architecture by further reducing the physical sub-element diameter. In this work, the diameter was reduced by 29% (Design 1) and 40% (Design 2), yielding hysteresis-loss reductions of 17% and 32%, respectively, while maintaining high critical current densities of 1,149 A/mm2 and 1,053 A/mm2 at 16 T. Additionally, the reduced-Dsub DBS wires exhibited high RRR values, further confirming the effectiveness of the refined design in maintaining consistent stability. These results demonstrate that sub-element size refinement enhances thermo-magnetic stability in DBS conductors, in agreement with trends observed in existing Nb3Sn studies, while preserving manufacturability and high-field transport performance. This study establishes reduced- Dsub DBS wires as promising candidates for next-generation high-field magnet applications.
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