In this paper, a strategy for the reactive power compensation and harmonic suppression of the power supply system in HT-7U superconductive Tokamak is proposed. The optimized approach is given in the parameters design...In this paper, a strategy for the reactive power compensation and harmonic suppression of the power supply system in HT-7U superconductive Tokamak is proposed. The optimized approach is given in the parameters design for passive filter. Also a controlling method with fast response time and good accuracy is put forward for the compensator, which is more suitable for the dynamic load.展开更多
By laser heated pedestal growth method, Bi_2Sr_2CaCu_2O_(8+δ) as-grown fibers with different morphologies were solidified in non-equilibrium condition at the rates of 0.1～14mm/min.At low rates,a(Sr_(1-x)Ca_x)CuO_2 p...By laser heated pedestal growth method, Bi_2Sr_2CaCu_2O_(8+δ) as-grown fibers with different morphologies were solidified in non-equilibrium condition at the rates of 0.1～14mm/min.At low rates,a(Sr_(1-x)Ca_x)CuO_2 phase with long and straight strips in shape and a white Cu-rich phase having a morphology of globular shape were found. With the increase of solidification rates,the phase (Sr_(1-x)Ca_x)CuO_2 becomes thinner and the Cu-rich phase becomes smaller and dispersive.When the solidification rates were last.another unstable phase(Sr_(1-x)Ca_x)Cu_2O_3 occurred.In fact,the tran- sition of the semiconductive as-grown fiber to the superconductor is a peritectoid reaction influenced by the annealing temperature and time.展开更多
Large area YBCO superconductive films prepared by d.c. magnetron sputtering have reached: T c>89 K, J c>3.5×10 6 A/cm 2 (77 K, 0 T), R s=0.25 mΩ, at 77.5 K, 9894 MHz. The microstructure an...Large area YBCO superconductive films prepared by d.c. magnetron sputtering have reached: T c>89 K, J c>3.5×10 6 A/cm 2 (77 K, 0 T), R s=0.25 mΩ, at 77.5 K, 9894 MHz. The microstructure analysis of the film showed it has fine monocrystalline structure and the crystalline perfectness is satisfactory. The oscillator, filter and antenna made from these films are good in performance. Therefore, YBCO superconductive films have great prospect in application.展开更多
As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,techno...As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,technology,more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials,instead of blindly pursuing the improvement of the superconducting transition temperature(T_(c)).In this paper,the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations.It has shown that Pb can withstand the compressive strain up to 10%while the lattice structure remains stable,indicated by the calculations of phonon band structures.From 0%to 10%compressive strain,there is neither a band-gap nor changing of the band structure.The.changing of electronic DOS.at the Fermi level leads to a decreasing of T_(c).Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure,which explains the reason why it has been used in practical productions.展开更多
We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit（SQC） pumped by microwave fields,and the use of such a SQC function as an artificial Λ-type three-level ...We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit（SQC） pumped by microwave fields,and the use of such a SQC function as an artificial Λ-type three-level atom.The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity,and the superluminal state is usually realized with a lower absorption.This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.展开更多
On the basis of the published literature and the interviews with some participants,this paper introduces the early history of the studies of superconductive materials and superconducting magnet during 1962～ 1966 in C...On the basis of the published literature and the interviews with some participants,this paper introduces the early history of the studies of superconductive materials and superconducting magnet during 1962～ 1966 in China,narrates the achievements of other relevant experimental and theoretical studies of superconductivity in that period briefly,and tries to give the authors' comments on that history.展开更多
The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and supe...The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform elec- trical transport measurement in ultra-high vaccum （UHV）. Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films.展开更多
Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fi...Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fiber rods obtained directly from LHPG method are semiconductive and after heat treatment at temperature range from 780 to 870℃,they transformed into superconductive wires.Triple junctions and sharp grain boundary exist in the sample.HREM studies showed the intergrowth of (010) and (110),the occasional missing of CaCuO_2 layer in the 2212 phase.展开更多
High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary am...High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary ambient oxygen pressure be 2-3 orders lower than that in pulsed laser deposition (PLD).Tc0 is 85-87 K,and Jc～1.0×106 A/cm2.Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm.High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.展开更多
Background In superconductive linear accelerator,the performance and stability can be impacted by gas adsorbed on cryogenic surfaces adversely.The cryogenic devices usually work at 4.2 K or 1.9 K and are refrigerated ...Background In superconductive linear accelerator,the performance and stability can be impacted by gas adsorbed on cryogenic surfaces adversely.The cryogenic devices usually work at 4.2 K or 1.9 K and are refrigerated by normal or super fluid liquid helium,respectively.Purpose The purpose of this paper is to study the character of gas migration in cryogenic tubes.Method Adsorption coefficient for hydrogen at 4.2 K is measured by experimental study.Then,a gas migration model is established based on the experimental results to depict the hydrogen migration process in cryogenic tubes.Results The experimental results and model analysis indicated that at cryogenic temperature(4.2 K),adsorption coefficient for hydrogen is very close to 1,which is several orders higher than the adsorption coefficient at room temperature,resulting in a unique pressure distribution pattern in cryogenic tubes when compared with the pressure distribution in room temperature tubes.Conclusions At 4.2 K or 1.9 K,the gas migration process is obviously different from the process at room temperature and is significantly affected by the gas adsorption on the cryogenic surfaces.The model established in this article can be applied not only to hydrogen migration in cryogenic tubes but also to other gas migration in tubes with high adsorption coefficient.展开更多
Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of...Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.展开更多
Superconducting radio-frequency(SRF)cavities are the core components of SRF linear accelerators,making their stable operation considerably important.However,the operational experience from different accelerator labora...Superconducting radio-frequency(SRF)cavities are the core components of SRF linear accelerators,making their stable operation considerably important.However,the operational experience from different accelerator laboratories has revealed that SRF faults are the leading cause of short machine downtime trips.When a cavity fault occurs,system experts analyze the time-series data recorded by low-level RF systems and identify the fault type.However,this requires expertise and intuition,posing a major challenge for control-room operators.Here,we propose an expert feature-based machine learning model for automating SRF cavity fault recognition.The main challenge in converting the"expert reasoning"process for SRF faults into a"model inference"process lies in feature extraction,which is attributed to the associated multidimensional and complex time-series waveforms.Existing autoregression-based feature-extraction methods require the signal to be stable and autocorrelated,resulting in difficulty in capturing the abrupt features that exist in several SRF failure patterns.To address these issues,we introduce expertise into the classification model through reasonable feature engineering.We demonstrate the feasibility of this method using the SRF cavity of the China accelerator facility for superheavy elements(CAFE2).Although specific faults in SRF cavities may vary across different accelerators,similarities exist in the RF signals.Therefore,this study provides valuable guidance for fault analysis of the entire SRF community.展开更多
The technology of electric propulsion aircraft(EPA)represents an important direction and an advanced stage in the development of aviation electrification.It is a key pathway for green development in aviation industry ...The technology of electric propulsion aircraft(EPA)represents an important direction and an advanced stage in the development of aviation electrification.It is a key pathway for green development in aviation industry and can significantly enhance the energy efficiency of aircraft propulsion system.Electric motor is the most critical electromechanical energy conversion component in an aircraft electric propulsion system(EPS).High-performance electric motors,power electronic converters and EPS control form the foundation of the EPA.This paper provides an overview of the characteristics of electric motors for EPA,analyzes the inverter topologies of EPSs,and reviews ongoing EPA projects.The article highlights the latest advancements in three types of motors:superconducting motors(SCMs),permanent magnet synchronous motors(PMSMs),and induction motors(IMs).It summarizes the control system architectures of current EPA initiatives and,building on this foundation,proposes future research directions for EPSs.These include cutting-edge areas such as high-performance motors and advanced manufacturing technologies,Ga N-or Si C-based inverter integration and innovation,electric propulsion control systems,and optimization of wiring systems.展开更多
Conventional superconducting nanowire single-photon detectors(SNSPDs)have been typically limited in their applications due to their size,weight,and power consumption,which confine their use to laboratory settings.Howe...Conventional superconducting nanowire single-photon detectors(SNSPDs)have been typically limited in their applications due to their size,weight,and power consumption,which confine their use to laboratory settings.However,with the rapid development of remote imaging,sensing technologies,and long-range quantum communication with fewer topographical constraints,the demand for high-efficiency single-photon detectors integrated with avionic platforms is rapidly growing.We herein designed and manufactured the first drone-based SNSPD system with a system detection efficiency(SDE)as high as 91.8%.This drone-based system incorporates high-performance NbTiN SNSPDs,a self-developed miniature liquid helium dewar,and custom-built integrated electrical setups,making it capable of being launched in complex topographical conditions.Such a drone-based SNSPD system may open the use of SNSPDs for applications that demand high SDE in complex environments.展开更多
Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes dev...Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium(Nb)cavity and the thick copper(Cu)layer’s high thermal conductivity and rigidity,thereby enhancing the operational stability of the bulk Nb cavities.This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities.We explored Cu-Nb composite superconducting cavities based on two technologies at the Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS),including their manufacturing processes,radio-frequency(RF)characteristics,and mechanical performance.These cavities exhibit robust mechanical stability.First,the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts.We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process.The cooling rates during the T_c crossing of Nb exerted a substantial impact on the performance of the cavities.Furthermore,we measured and analyzed the surface resistance R_(s)attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events.Second,for the first time,a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology.We achieved a high peak electric field E_(pk)of~88.8 MV/m at 2 K and the unloaded quality factor Q_(0)at the E_(pk)of 88.8 MV/m exceeded 1×10^(10).This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu-Nb composite superconducting cavity with superior thermal stability.The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.展开更多
A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface supercond...A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.展开更多
Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for...Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for high-temperature superconductors, as both Im3m YH_(6) and Im3m CaH_(6) exhibit similar structures and excellent superconducting properties, while Y and Ca atoms possess close atomic radii and electronegativities.Here, we report the successful synthesis of Im3m(Y, Ca)H_(6) achieving a maximum superconducting transition temperature(T_(c)) approximately 224 K at 155 GPa through five independent high-temperature and high-pressure experiments. Remarkably, the T_(c) of Im3m(Y, Ca)H_(6) remains highly stable(ΔT_(c) ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im3m CaH_(6) and Im3m YH_(6). The enhanced superconducting properties may stem from the cooperative chemical template effect of Y and Ca atoms near the s-d border, which significantly reinforces H lattice stability and thus maintains superior superconductivity.This study highlights the potential of multicomponent cooperative effects in designing hydride superconductors,offering new insights for achieving high-T_(c) hydrides at lower pressures in the future.展开更多
Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transit...Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.展开更多
Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among th...Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).展开更多
文摘In this paper, a strategy for the reactive power compensation and harmonic suppression of the power supply system in HT-7U superconductive Tokamak is proposed. The optimized approach is given in the parameters design for passive filter. Also a controlling method with fast response time and good accuracy is put forward for the compensator, which is more suitable for the dynamic load.
基金This work was supported by the National Natural Science Foundation of Chinathe National Laboratory of Rapidly Solidified Non-equilibrium Alloys,Institute of Metal Research,Academia Sinica
文摘By laser heated pedestal growth method, Bi_2Sr_2CaCu_2O_(8+δ) as-grown fibers with different morphologies were solidified in non-equilibrium condition at the rates of 0.1～14mm/min.At low rates,a(Sr_(1-x)Ca_x)CuO_2 phase with long and straight strips in shape and a white Cu-rich phase having a morphology of globular shape were found. With the increase of solidification rates,the phase (Sr_(1-x)Ca_x)CuO_2 becomes thinner and the Cu-rich phase becomes smaller and dispersive.When the solidification rates were last.another unstable phase(Sr_(1-x)Ca_x)Cu_2O_3 occurred.In fact,the tran- sition of the semiconductive as-grown fiber to the superconductor is a peritectoid reaction influenced by the annealing temperature and time.
文摘Large area YBCO superconductive films prepared by d.c. magnetron sputtering have reached: T c>89 K, J c>3.5×10 6 A/cm 2 (77 K, 0 T), R s=0.25 mΩ, at 77.5 K, 9894 MHz. The microstructure analysis of the film showed it has fine monocrystalline structure and the crystalline perfectness is satisfactory. The oscillator, filter and antenna made from these films are good in performance. Therefore, YBCO superconductive films have great prospect in application.
文摘As one of the main materials in the practical application.of superconductor,lead(Pb)has been used to manufacture superconducting AC power cable,and some weak current fields.With the development of manufacturing,technology,more and more researchers focus on exploring the physical and chemical properties of cryogenic superconducting materials,instead of blindly pursuing the improvement of the superconducting transition temperature(T_(c)).In this paper,the structural properties and superconducting transition temperature under high pressure of Pb have been studied by first-principles calculations.It has shown that Pb can withstand the compressive strain up to 10%while the lattice structure remains stable,indicated by the calculations of phonon band structures.From 0%to 10%compressive strain,there is neither a band-gap nor changing of the band structure.The.changing of electronic DOS.at the Fermi level leads to a decreasing of T_(c).Our calculations show that Pb is a stable elemental metallic superconductor even under high pressure,which explains the reason why it has been used in practical productions.
基金Project supported by the National Natural Science Foundation of China (Grant No. 111174040)the Fundamental Research Funds for the Central Universities
文摘We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit（SQC） pumped by microwave fields,and the use of such a SQC function as an artificial Λ-type three-level atom.The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity,and the superluminal state is usually realized with a lower absorption.This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.
文摘On the basis of the published literature and the interviews with some participants,this paper introduces the early history of the studies of superconductive materials and superconducting magnet during 1962～ 1966 in China,narrates the achievements of other relevant experimental and theoretical studies of superconductivity in that period briefly,and tries to give the authors' comments on that history.
基金supported by the National Basic Research Program of China(Grant Nos.2013CB921902 and 2011CB922200)the National Natural Science Foundation of China(Grant Nos.11227404,11274228,11521404,11174199,and 11134008)
文摘The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform elec- trical transport measurement in ultra-high vaccum （UHV）. Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films.
文摘Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fiber rods obtained directly from LHPG method are semiconductive and after heat treatment at temperature range from 780 to 870℃,they transformed into superconductive wires.Triple junctions and sharp grain boundary exist in the sample.HREM studies showed the intergrowth of (010) and (110),the occasional missing of CaCuO_2 layer in the 2212 phase.
基金This work was supported by the State Key Program of China (Grant No. G1998061412) the National 863 Project (Grant No. 863-CD070103) .
文摘High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary ambient oxygen pressure be 2-3 orders lower than that in pulsed laser deposition (PLD).Tc0 is 85-87 K,and Jc～1.0×106 A/cm2.Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm.High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.
文摘Background In superconductive linear accelerator,the performance and stability can be impacted by gas adsorbed on cryogenic surfaces adversely.The cryogenic devices usually work at 4.2 K or 1.9 K and are refrigerated by normal or super fluid liquid helium,respectively.Purpose The purpose of this paper is to study the character of gas migration in cryogenic tubes.Method Adsorption coefficient for hydrogen at 4.2 K is measured by experimental study.Then,a gas migration model is established based on the experimental results to depict the hydrogen migration process in cryogenic tubes.Results The experimental results and model analysis indicated that at cryogenic temperature(4.2 K),adsorption coefficient for hydrogen is very close to 1,which is several orders higher than the adsorption coefficient at room temperature,resulting in a unique pressure distribution pattern in cryogenic tubes when compared with the pressure distribution in room temperature tubes.Conclusions At 4.2 K or 1.9 K,the gas migration process is obviously different from the process at room temperature and is significantly affected by the gas adsorption on the cryogenic surfaces.The model established in this article can be applied not only to hydrogen migration in cryogenic tubes but also to other gas migration in tubes with high adsorption coefficient.
基金supported by the National Natural Science Foundation of China(12072136).
文摘Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.
基金supported by the studies of intelligent LLRF control algorithms for superconducting RF cavities(No.E129851YR0)the National Natural Science Foundation of China(No.U22A20261)Applications of Artificial Intelligence in the Stability Study of Superconducting Linear Accelerators(No.E429851YR0)。
文摘Superconducting radio-frequency(SRF)cavities are the core components of SRF linear accelerators,making their stable operation considerably important.However,the operational experience from different accelerator laboratories has revealed that SRF faults are the leading cause of short machine downtime trips.When a cavity fault occurs,system experts analyze the time-series data recorded by low-level RF systems and identify the fault type.However,this requires expertise and intuition,posing a major challenge for control-room operators.Here,we propose an expert feature-based machine learning model for automating SRF cavity fault recognition.The main challenge in converting the"expert reasoning"process for SRF faults into a"model inference"process lies in feature extraction,which is attributed to the associated multidimensional and complex time-series waveforms.Existing autoregression-based feature-extraction methods require the signal to be stable and autocorrelated,resulting in difficulty in capturing the abrupt features that exist in several SRF failure patterns.To address these issues,we introduce expertise into the classification model through reasonable feature engineering.We demonstrate the feasibility of this method using the SRF cavity of the China accelerator facility for superheavy elements(CAFE2).Although specific faults in SRF cavities may vary across different accelerators,similarities exist in the RF signals.Therefore,this study provides valuable guidance for fault analysis of the entire SRF community.
基金supported by the National Nature Science Foundation of China(Grant No.52302507)。
文摘The technology of electric propulsion aircraft(EPA)represents an important direction and an advanced stage in the development of aviation electrification.It is a key pathway for green development in aviation industry and can significantly enhance the energy efficiency of aircraft propulsion system.Electric motor is the most critical electromechanical energy conversion component in an aircraft electric propulsion system(EPS).High-performance electric motors,power electronic converters and EPS control form the foundation of the EPA.This paper provides an overview of the characteristics of electric motors for EPA,analyzes the inverter topologies of EPSs,and reviews ongoing EPA projects.The article highlights the latest advancements in three types of motors:superconducting motors(SCMs),permanent magnet synchronous motors(PMSMs),and induction motors(IMs).It summarizes the control system architectures of current EPA initiatives and,building on this foundation,proposes future research directions for EPSs.These include cutting-edge areas such as high-performance motors and advanced manufacturing technologies,Ga N-or Si C-based inverter integration and innovation,electric propulsion control systems,and optimization of wiring systems.
基金the Innovation Program for Quantum Science and Technology(Grant No.2023ZD0300100)the National Key Research and Development Program of China(Grant Nos.2023YFB3809600 and 2023YFC3007801)+1 种基金the National Natural Science Foundation of China(Grant Nos.62301543 and U24A20320)the Shanghai Sailing Program(Grant No.21YF1455700).
文摘Conventional superconducting nanowire single-photon detectors(SNSPDs)have been typically limited in their applications due to their size,weight,and power consumption,which confine their use to laboratory settings.However,with the rapid development of remote imaging,sensing technologies,and long-range quantum communication with fewer topographical constraints,the demand for high-efficiency single-photon detectors integrated with avionic platforms is rapidly growing.We herein designed and manufactured the first drone-based SNSPD system with a system detection efficiency(SDE)as high as 91.8%.This drone-based system incorporates high-performance NbTiN SNSPDs,a self-developed miniature liquid helium dewar,and custom-built integrated electrical setups,making it capable of being launched in complex topographical conditions.Such a drone-based SNSPD system may open the use of SNSPDs for applications that demand high SDE in complex environments.
基金supported by the Large Research Infrastructures China initiative Accelerator Driven System(No.2017-000052-75-01-000590)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2022422)+1 种基金the Young Scientists of National Natural Science Foundation of China(No.12005275)the Advanced Energy Science and Technology Guangdong Laboratory(No.HND22PTZZYY)。
文摘Theoretically,copper–niobium(Cu-Nb)composite superconducting cavities have excellent potential for high thermal and mechanical stability.They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium(Nb)cavity and the thick copper(Cu)layer’s high thermal conductivity and rigidity,thereby enhancing the operational stability of the bulk Nb cavities.This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities.We explored Cu-Nb composite superconducting cavities based on two technologies at the Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS),including their manufacturing processes,radio-frequency(RF)characteristics,and mechanical performance.These cavities exhibit robust mechanical stability.First,the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts.We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process.The cooling rates during the T_c crossing of Nb exerted a substantial impact on the performance of the cavities.Furthermore,we measured and analyzed the surface resistance R_(s)attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events.Second,for the first time,a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology.We achieved a high peak electric field E_(pk)of~88.8 MV/m at 2 K and the unloaded quality factor Q_(0)at the E_(pk)of 88.8 MV/m exceeded 1×10^(10).This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu-Nb composite superconducting cavity with superior thermal stability.The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.
基金supported by the National Natural Science Foundation of China(Grant No.62488201)the National Key Research and Development Projects of China(Grant Nos.2022YFA1204100 and 2023YFA1607400)+1 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)the Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700)。
文摘A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states.Trigonal γ-PtBi_(2),a superconductor,is a promising candidate,as both surface superconducting gaps and topological surface states have been observed.However,the simultaneous presence of bulk and surface superconductivity has remained unresolved.In this study,we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 using ultra-low-temperature scanning tunneling microscopy/spectroscopy.The bulk gap,Δ,is∼0.053 meV,with a critical temperature(T_(c))of∼0.5K and a critical field below 0.01 T,accompanied by a vortex lattice and vortex bound states and yielding a coherence length of∼200 nm.Remarkably,certain surface regions exhibit a much larger gap(Δ)of∼0.42 meV,persisting up to a T_(c)value of∼3K and surviving magnetic fields of up to 2 T,yet lacking a static vortex lattice.This coexistence of robust surface and bulk superconductivity establishes γ-PtBi_(2)as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1405500)the National Natural Science Foundation of China (Grant No.52372257)。
文摘Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for high-temperature superconductors, as both Im3m YH_(6) and Im3m CaH_(6) exhibit similar structures and excellent superconducting properties, while Y and Ca atoms possess close atomic radii and electronegativities.Here, we report the successful synthesis of Im3m(Y, Ca)H_(6) achieving a maximum superconducting transition temperature(T_(c)) approximately 224 K at 155 GPa through five independent high-temperature and high-pressure experiments. Remarkably, the T_(c) of Im3m(Y, Ca)H_(6) remains highly stable(ΔT_(c) ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im3m CaH_(6) and Im3m YH_(6). The enhanced superconducting properties may stem from the cooperative chemical template effect of Y and Ca atoms near the s-d border, which significantly reinforces H lattice stability and thus maintains superior superconductivity.This study highlights the potential of multicomponent cooperative effects in designing hydride superconductors,offering new insights for achieving high-T_(c) hydrides at lower pressures in the future.
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403900 and 2021YFA1401800)the NSF of China(Grant Nos.U2032214,12122414,12104487,and 12004419)+2 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)support from the Youth Innovation Promotion Association of the CAS(2019008)supported by the Synergetic Extreme Condition User Facility(SECUF)。
文摘Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.
基金supported by the National Nature Science Foundation of China[Grant Nos.92365204 and 12274298(Z.K.Liu)]the National Key R&D program of China[Grant No.2022YFA1604400/03(Z.K.Liu)]Zhangjiang Laboratory(Y.M.Zhang).The authors thank BL02B at the Shanghai Synchrotron Radiation Facility supported by the National Natural Science Foundation of China(Contract No.11227902).
文摘Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).
