The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic fi...The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic field were formed after the partial-melting and solidification in 8 T magnetic field, and transformed into the Bi-2223 grains with c-axis alignment during the further sintering process at 840 ℃ without magnetic field. The conversion of Bi-2212 grains to Bi-2223 grains has the heredity in grain alignment. The mixed structures of the Bi-2223 and the Bi-2212 grains with their c-axis parallel to the magnetic field are formed in samples sintered at 850?855 ℃ in 10 T magnetic field. When sintered in 10 T below 845 ℃, a high proportion of Bi-2223 phase is obtained, however no preferred orientation is observed. The Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 ℃ for 120 h in a 15 ℃/cm temperature gradient without magnetic field. Moreover, the samples sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase.展开更多
The electromagnetic characteristics and iron loss of a high-temperature superconductor wind generator(HWG)equipped with an overlapped field coil arrangement(OFCA)are studied by comparing with the one equipped with the...The electromagnetic characteristics and iron loss of a high-temperature superconductor wind generator(HWG)equipped with an overlapped field coil arrangement(OFCA)are studied by comparing with the one equipped with the conventional field coil arrangement(CFCA).Through a quantitative analysis,it was found that HWG with OFCA exhibits better electromagnetic characteristics than HWG with CFCA and can reduce the iron loss by eliminating the magnetic flux sag caused by the adjacent field coil sides with the same current flow direction.In addition,the OFCA topology can further reduce the volume of the wind generator.展开更多
The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenb...The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenberg model, we present the evolution of magnetic structures on magnetic field in RFeAsO(R = Ce, Pr, Nd, Sm, Gd, and Tb) and RFe_2As_2(R =Eu) compounds. It is found that spin-flop transition occurs in both rare-earth and iron layers under magnetic field, in good agreement with the experimental results. The interplay between rare-earth and iron spins plays a key role in the magneticfield-driven magnetic phase transition, which suggests that the rare-earth layers can modulate the magnetic behaviors of iron layers. In addition, the factors that affect the critical magnetic field for spin-flop transition are also discussed.展开更多
Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exo...Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exotic lower-dimensional boundary modes,such as Majorana corner and hinge modes.However,higher-order topological superconductivity has yet to be found in naturally occurring materials.We investigate higher-order topology in a two-dimensional Josephson junction comprised of two s-wave superconductors separated by a topological insulator thin film.We find that zero-energy Majorana corner modes,a boundary fingerprint of higherorder topological superconductivity,can be achieved by applying magnetic field.When an in-plane Zeeman field is applied to the system,two corner modes appear in the superconducting junction.Furthermore,we also discover a two-dimensional nodal superconducting phase which supports flat-band Majorana edge modes connecting the bulk nodes.Importantly,we demonstrate that zero-energy Majorana corner modes are stable when increasing the thickness of topological insulator thin film.展开更多
The discovery of superconductivity in quasi-one-dimensional Cr-based pnictides A2Cr3As3(A = alkali metals) has generated considerable research interest, primarily owing to their reduced dimensionality, significant e...The discovery of superconductivity in quasi-one-dimensional Cr-based pnictides A2Cr3As3(A = alkali metals) has generated considerable research interest, primarily owing to their reduced dimensionality, significant electron correlations,and possible unconventional superconductivity. The upper critical field(Hc2) provides important information on the superconducting pairing. In this paper, we first briefly overview the latest research progress on the Cr-based superconductors.Then, we introduce typical Hc2(T) behaviors of type-II superconductors in relation with the pair-breaking mechanisms.After a description of the measurement method for Hc2, we focus on the analysis of Hc2 data, especially for the temperature and angle dependence, in K2Cr3As3 crystals. The result indicates(i) an absence of Pauli-paramagnetic pair breaking for field perpendicular to the Cr3As3 chains, and(ii) a unique threefold modulation for the in-plane Hc2Φ profile. Finally we conclude with remarks on the possible unconventional superconducting pairing symmetry.展开更多
This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppressio...This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppression and static var. compensation, and AC power system, the design principle and features are introduced, the design scheme and R & D progress are described, the simulation studies and laboratory test are presented too.展开更多
The HT-7U super-conducting tokamak is a full super-conducting magnetically confined fusion device, It mainly consists of super-conducting toroidal field (TF) coils and super conducting poloidal field (PF) coils. This...The HT-7U super-conducting tokamak is a full super-conducting magnetically confined fusion device, It mainly consists of super-conducting toroidal field (TF) coils and super conducting poloidal field (PF) coils. This paper describes the distribution of magnetic field, ripple and electromagnetic loads of TF system, some results are necessary to analyze and calculate the stresses and deformation on TF system by a finite element method. Meanwhile, in this paper, the main scope of the calculation is carried out for the case of constant magnetic field on conductor of the TF coil winding in order to provide electromagnet parameters for the quench analysis of Cable-in-Conduit Conductor (CICC) of TF system in HT-7U.展开更多
HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating toka...HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating tokama-k fusion reactor. This paper describes only a toroidal field (TF) superconducting magnet system of HT7U. In this paper, design criteria of conductor and stability analysis, coil winding and support structure design of magnet system, mechanical calculation and stress analysis, heat load evaluation are given.展开更多
Large superconducting Fe Se crystals of(001) orientation have been prepared via a hydrothermal ion release/introduction route for the first time. The hydrothermally derived Fe Se crystals are up to 10 mm×5 mm...Large superconducting Fe Se crystals of(001) orientation have been prepared via a hydrothermal ion release/introduction route for the first time. The hydrothermally derived Fe Se crystals are up to 10 mm×5 mm×0.3 mm in dimension. The pure tetragonal FeSe phase has been confirmed by x-ray diffraction(XRD) and the composition determined by both inductively coupled plasma atomic emission spectroscopy(ICP-AES) and energy dispersive x-ray spectroscopy(EDX). The superconducting transition of the Fe Se samples has been characterized by magnetic and transport measurements. The zero-temperature upper critical field H(c2) is calculated to be 13.2–16.7 T from a two-band model. The normal-state cooperative paramagnetism is found to be predominated by strong spin frustrations below the characteristic temperature T(sn), where the Ising spin nematicity has been discerned in the FeSe superconductor crystals as reported elsewhere.展开更多
High Tc Superconductors (HTS) have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical a...High Tc Superconductors (HTS) have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical appfications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS appfications such as for HTS magnetic levitation application.展开更多
The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA an...The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA and the major and minor radius are 1.78 m and 0.4m respectively, with an elongation of 1.85. The preliminary engineering design of the poloidal field (PF) and toroidal field (TF) magnet systems have been done. The PF system is composed of twelve superconducting coils located symmetrically about the equator plane. The central solenoid (CS) assembly is formed by six coils. The TF system consists of 16 superconducting coils. The NbTi cable-in-conduit conductor or (CICC) cooled by a supercritical helium at 4.5 K is chosen as a superconductor for all of the PF and TF coils. At this temperature, the peak magnetic field on the PF magnets is about 4.51 T .The maximum volt-second capacity and the duration of plasma inductive discharge are about 10 Vs and 10 seconds respectively. The stray field in plasma initial region is quite low ( 1.5× 10 -3 T). The magnetic field on the TF magnet is 5.8 T while the toroidal field at the center of the device (R = 1.7 m) is 3.5 T and the ripple of the TF is less than 0.62% at the outer plasma surface (R = 2.1 m). All of the PF and TF magnets are stable during all modes of operation including the plasma disruption. The final design of the PF system is the result of an iterative process involving the use of equilibrium code EQT, magnetic code EFFI, and other codes, which have been developed by our designing group.展开更多
A cryogenic low noise amplifier (LNA) using Agilent high electron mobility transistor (HEMT) for 380 MHzto 480 MHz is designed and fabricated, and the excellent cryogenic performance in superconducting receiver fr...A cryogenic low noise amplifier (LNA) using Agilent high electron mobility transistor (HEMT) for 380 MHzto 480 MHz is designed and fabricated, and the excellent cryogenic performance in superconducting receiver front-end for communication system is achieved. A special input impedance matching topology is implemented to provide low noise figure (NF) and good input matching in this cryogenic LNA design. The measurement results show that the NF is within 0.25 dB from the minimum NF of a single transistor, the power gain is above 20 dB, the flatness is within 1 dB, and the maximum input return loss is lower than -20 dB in bandwidth.展开更多
This paper introduces the relevant parameters and related characteristics of the LabVIEW and PCI6221 data acquisition (DAQ) card, describes in detail the approach of building the measure and control platform of virt...This paper introduces the relevant parameters and related characteristics of the LabVIEW and PCI6221 data acquisition (DAQ) card, describes in detail the approach of building the measure and control platform of virtual instrument (VI) using LabVIEW and PCI6221, specifically discusses the system's application in high temperature superconductor (HTS) research including the test of HTS volt-ampere characteristics and the HTS magnetic energy storage. The experiments prove that the VI test and control system is easy to build and convenient to use.展开更多
文摘The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic field were formed after the partial-melting and solidification in 8 T magnetic field, and transformed into the Bi-2223 grains with c-axis alignment during the further sintering process at 840 ℃ without magnetic field. The conversion of Bi-2212 grains to Bi-2223 grains has the heredity in grain alignment. The mixed structures of the Bi-2223 and the Bi-2212 grains with their c-axis parallel to the magnetic field are formed in samples sintered at 850?855 ℃ in 10 T magnetic field. When sintered in 10 T below 845 ℃, a high proportion of Bi-2223 phase is obtained, however no preferred orientation is observed. The Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 ℃ for 120 h in a 15 ℃/cm temperature gradient without magnetic field. Moreover, the samples sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase.
基金partly supported by the National Natural Science Foundation of China under Grants No.61473061 and No.61104104the Sichuan Science and Technology Program under Grant No.2020YFSY0012the Program for New Century Excellent Talents in University under Grant No.NCET-13-0091。
文摘The electromagnetic characteristics and iron loss of a high-temperature superconductor wind generator(HWG)equipped with an overlapped field coil arrangement(OFCA)are studied by comparing with the one equipped with the conventional field coil arrangement(CFCA).Through a quantitative analysis,it was found that HWG with OFCA exhibits better electromagnetic characteristics than HWG with CFCA and can reduce the iron loss by eliminating the magnetic flux sag caused by the adjacent field coil sides with the same current flow direction.In addition,the OFCA topology can further reduce the volume of the wind generator.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11104274,11274310,and 11474287)the Fundamental Research Funds for the Central Universities,China(Grant No.27R1310020A)
文摘The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenberg model, we present the evolution of magnetic structures on magnetic field in RFeAsO(R = Ce, Pr, Nd, Sm, Gd, and Tb) and RFe_2As_2(R =Eu) compounds. It is found that spin-flop transition occurs in both rare-earth and iron layers under magnetic field, in good agreement with the experimental results. The interplay between rare-earth and iron spins plays a key role in the magneticfield-driven magnetic phase transition, which suggests that the rare-earth layers can modulate the magnetic behaviors of iron layers. In addition, the factors that affect the critical magnetic field for spin-flop transition are also discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074108,11974256,and 12147102)the Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutionthe Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQMSX0568)。
文摘Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exotic lower-dimensional boundary modes,such as Majorana corner and hinge modes.However,higher-order topological superconductivity has yet to be found in naturally occurring materials.We investigate higher-order topology in a two-dimensional Josephson junction comprised of two s-wave superconductors separated by a topological insulator thin film.We find that zero-energy Majorana corner modes,a boundary fingerprint of higherorder topological superconductivity,can be achieved by applying magnetic field.When an in-plane Zeeman field is applied to the system,two corner modes appear in the superconducting junction.Furthermore,we also discover a two-dimensional nodal superconducting phase which supports flat-band Majorana edge modes connecting the bulk nodes.Importantly,we demonstrate that zero-energy Majorana corner modes are stable when increasing the thickness of topological insulator thin film.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674281 and 11574097)the Fundamental Research Funds for the Central Universities of China
文摘The discovery of superconductivity in quasi-one-dimensional Cr-based pnictides A2Cr3As3(A = alkali metals) has generated considerable research interest, primarily owing to their reduced dimensionality, significant electron correlations,and possible unconventional superconductivity. The upper critical field(Hc2) provides important information on the superconducting pairing. In this paper, we first briefly overview the latest research progress on the Cr-based superconductors.Then, we introduce typical Hc2(T) behaviors of type-II superconductors in relation with the pair-breaking mechanisms.After a description of the measurement method for Hc2, we focus on the analysis of Hc2 data, especially for the temperature and angle dependence, in K2Cr3As3 crystals. The result indicates(i) an absence of Pauli-paramagnetic pair breaking for field perpendicular to the Cr3As3 chains, and(ii) a unique threefold modulation for the in-plane Hc2Φ profile. Finally we conclude with remarks on the possible unconventional superconducting pairing symmetry.
文摘This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppression and static var. compensation, and AC power system, the design principle and features are introduced, the design scheme and R & D progress are described, the simulation studies and laboratory test are presented too.
文摘The HT-7U super-conducting tokamak is a full super-conducting magnetically confined fusion device, It mainly consists of super-conducting toroidal field (TF) coils and super conducting poloidal field (PF) coils. This paper describes the distribution of magnetic field, ripple and electromagnetic loads of TF system, some results are necessary to analyze and calculate the stresses and deformation on TF system by a finite element method. Meanwhile, in this paper, the main scope of the calculation is carried out for the case of constant magnetic field on conductor of the TF coil winding in order to provide electromagnet parameters for the quench analysis of Cable-in-Conduit Conductor (CICC) of TF system in HT-7U.
文摘HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating tokama-k fusion reactor. This paper describes only a toroidal field (TF) superconducting magnet system of HT7U. In this paper, design criteria of conductor and stability analysis, coil winding and support structure design of magnet system, mechanical calculation and stress analysis, heat load evaluation are given.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574370,11274358,and 11190020)the National Basic Research Program of China(Grant No.2013CB921700)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020100)
文摘Large superconducting Fe Se crystals of(001) orientation have been prepared via a hydrothermal ion release/introduction route for the first time. The hydrothermally derived Fe Se crystals are up to 10 mm×5 mm×0.3 mm in dimension. The pure tetragonal FeSe phase has been confirmed by x-ray diffraction(XRD) and the composition determined by both inductively coupled plasma atomic emission spectroscopy(ICP-AES) and energy dispersive x-ray spectroscopy(EDX). The superconducting transition of the Fe Se samples has been characterized by magnetic and transport measurements. The zero-temperature upper critical field H(c2) is calculated to be 13.2–16.7 T from a two-band model. The normal-state cooperative paramagnetism is found to be predominated by strong spin frustrations below the characteristic temperature T(sn), where the Ising spin nematicity has been discerned in the FeSe superconductor crystals as reported elsewhere.
文摘High Tc Superconductors (HTS) have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical appfications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS appfications such as for HTS magnetic levitation application.
文摘The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA and the major and minor radius are 1.78 m and 0.4m respectively, with an elongation of 1.85. The preliminary engineering design of the poloidal field (PF) and toroidal field (TF) magnet systems have been done. The PF system is composed of twelve superconducting coils located symmetrically about the equator plane. The central solenoid (CS) assembly is formed by six coils. The TF system consists of 16 superconducting coils. The NbTi cable-in-conduit conductor or (CICC) cooled by a supercritical helium at 4.5 K is chosen as a superconductor for all of the PF and TF coils. At this temperature, the peak magnetic field on the PF magnets is about 4.51 T .The maximum volt-second capacity and the duration of plasma inductive discharge are about 10 Vs and 10 seconds respectively. The stray field in plasma initial region is quite low ( 1.5× 10 -3 T). The magnetic field on the TF magnet is 5.8 T while the toroidal field at the center of the device (R = 1.7 m) is 3.5 T and the ripple of the TF is less than 0.62% at the outer plasma surface (R = 2.1 m). All of the PF and TF magnets are stable during all modes of operation including the plasma disruption. The final design of the PF system is the result of an iterative process involving the use of equilibrium code EQT, magnetic code EFFI, and other codes, which have been developed by our designing group.
基金This work was supported by the National Nature Science Foundation of China under Grant No. 60471001.
文摘A cryogenic low noise amplifier (LNA) using Agilent high electron mobility transistor (HEMT) for 380 MHzto 480 MHz is designed and fabricated, and the excellent cryogenic performance in superconducting receiver front-end for communication system is achieved. A special input impedance matching topology is implemented to provide low noise figure (NF) and good input matching in this cryogenic LNA design. The measurement results show that the NF is within 0.25 dB from the minimum NF of a single transistor, the power gain is above 20 dB, the flatness is within 1 dB, and the maximum input return loss is lower than -20 dB in bandwidth.
文摘This paper introduces the relevant parameters and related characteristics of the LabVIEW and PCI6221 data acquisition (DAQ) card, describes in detail the approach of building the measure and control platform of virtual instrument (VI) using LabVIEW and PCI6221, specifically discusses the system's application in high temperature superconductor (HTS) research including the test of HTS volt-ampere characteristics and the HTS magnetic energy storage. The experiments prove that the VI test and control system is easy to build and convenient to use.