The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive se...The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%展开更多
Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of ...Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current＇s strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin- polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks＇ position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.展开更多
Current leads are used to connect the superconducting magnets in cryogenic temperature to the power station in room temperature. It is the main source of heat leak into the cryostat of magnets on static operation. Thi...Current leads are used to connect the superconducting magnets in cryogenic temperature to the power station in room temperature. It is the main source of heat leak into the cryostat of magnets on static operation. This paper presents the optimized methods of the leads for BEPCⅡ, and the effects of different cross section area on the heat leak, temperature profile as well as the voltage drop of the leads. The multi-tube structure is adopted and improved for the leads. The results of numerical simulation using CFD software package Fluent6.0 for the multi-tube-structure leads are presented, which can be used to improve the design of the leads.展开更多
It′s important that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting syste...It′s important that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting system conduction cooled by GM coolers. This paper presents an experimental investigation into the effects of pure Ag and AgAu alloys sheath materials on the properties of Bi(2223) multifilamentary tapes and the optimisation of conduction cooled hybrid current leads made from copper and Bi(2223)/Ag or Bi(2223)/AgAu tapes. The thermal conductivity of the tapes were measured by cryogenic steady heat flux method and the resistance was measured by using standard DC four probe method at low temperature. The results showed that the reduction of thermal conductivity by the addition of Au into the sheath material of Bi(2223) tapes was 65 0 0, 75 0 0 and 85 0 0 lower than that of pure Ag sheathed Bi(2223) tapes and the increase of resistivity was 4.9 , 10 and 19.4 times higher than that of pure Ag for the addition of 2.2 0 0, 5.7 0 0 and 10.7 0 0Au(atom ratio) respectively. And the study also attempts to optimise thermodynamically the conduction cooled hybrid current lead by using a developed model, which took the irreversibility of commercial GM coolers, the contact resistance and thermal conductance into account. Predictions from the model showed that AgAu alloys were suitable candidate materials to replace Ag as sheath material of Bi(2223) tapes applied in HTS current leads. In addition, Bi(2223)/AgAu was a suitable material to be applied as the HTS section of hybrid current leads in conduction cooled superconducting electric systems.展开更多
The α-PbO2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properti...The α-PbO2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO2 electrodes. The physic- ochemical properties of the α-PbO2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry （LSV） and A.C. impedance. A compact and uniform layer of lead dioxide ：）vas obtained at the current density of 3 mA.cm-2. A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO2. The corrosion resistance of α-PbO2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities in aqueous Zn2＋ 50 g·L^-1, H2SO4 150 When used as anodes for oxygen evolution g·L^-1, the Al/conductive coating/α-PbO2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA·cm^-2. The lowest roughnest factor was obtained at 1 mA·cm^-2.展开更多
An experimental Paschen test setup has been established to analyze the quality of ITER current lead （CL） insulation and extend the research on Paschen＇s law under various conditions. Insulation problems can destroy...An experimental Paschen test setup has been established to analyze the quality of ITER current lead （CL） insulation and extend the research on Paschen＇s law under various conditions. Insulation problems can destroy a machine if a Paschen discharge is triggered by an insulation defect that is caused by faulty manufacturing, electromagnetic force, and thermal stress load with a certain degree of vacuum helium or pipe leakage. The results show that the CL insulation mock-up worked well under normal temperature and pressure. Besides, the mock-up also worked well in helium conditions and at 80 K temperature at different pressures. One area of CL insulation was severely destroyed when the 80 K test was conducted after 5 thermal cycles, resulting in Paschen discharge phenomenon. The breakdown voltage is maintained at a relatively low level under different pressure conditions; the change of breakdown voltage was mainly due to the change of pressure, and such change was in line with the Paschen law.展开更多
The possibility of using Pb-electroplated reticulated SiC as the positive current collector for lead-acid batteries was investigated. Reticulated SiC with two aperture sizes (3 and 2mm) were tested as the substrate of...The possibility of using Pb-electroplated reticulated SiC as the positive current collector for lead-acid batteries was investigated. Reticulated SiC with two aperture sizes (3 and 2mm) were tested as the substrate of positive electrode. It was found that the reticulated SiC has an excellent corrosion resistance in H2SO4 solution, and the Pb layer electroplated on reticulated SiC showed analogous electrochemical behavior to metal Pb. Preliminary test of the battery performance indicated that the utilization efficiency of the positive active mass of new designed batteries are improved compared with the conventional batteries. The improvement could be ascribed to the high specific surface area of the reticulated structured positive current collector, which was further supported by the even better performance of the battery made from a smaller aperture size (2mm) reticulated SiC as the substrate of the positive electrode.展开更多
PTC热敏陶瓷的无铅化是绿色智能加热及电路智能保护元件研制的重要前提。为了获得可在空气气氛下烧结且兼具高居里温度和高升阻比的无铅化PTC热敏陶瓷,本工作采用固相法制备了(1-x)BaTiO_(3)-0.5 x Bi_(0.5)Na_(0.5)TiO_(3)-0.5 x Bi_(0...PTC热敏陶瓷的无铅化是绿色智能加热及电路智能保护元件研制的重要前提。为了获得可在空气气氛下烧结且兼具高居里温度和高升阻比的无铅化PTC热敏陶瓷,本工作采用固相法制备了(1-x)BaTiO_(3)-0.5 x Bi_(0.5)Na_(0.5)TiO_(3)-0.5 x Bi_(0.5)K_(0.5)TiO_(3)和0.98BaTiO_(3)-0.02 y Bi0.5 Na_(0.5)TiO_(3)-0.02(1-y)Bi_(0.5)K_(0.5)TiO_(3)三元固溶体系无铅PTC热敏陶瓷材料,研究了不同含量的Na和K元素对无铅PTC热敏陶瓷材料的烧结特性和电学性能的影响。结果表明,BNT和BKT均与BaTiO_(3)形成固溶体,随着BNT含量的增加,PTC陶瓷平均晶粒尺寸减小,当BNT和BKT含量相同时,PTC陶瓷可以在较宽的烧结温度范围内实现半导化,且在空气气氛下烧结温度为1200℃的陶瓷样品具有最佳的PTC效应,其室温电阻率为128Ω·cm,升阻比为5个数量级,居里温度为142℃。展开更多
文摘The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%
基金Supported by the National Natural Science Foundation of China under Grant No 61274101
文摘Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current＇s strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin- polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks＇ position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.
文摘Current leads are used to connect the superconducting magnets in cryogenic temperature to the power station in room temperature. It is the main source of heat leak into the cryostat of magnets on static operation. This paper presents the optimized methods of the leads for BEPCⅡ, and the effects of different cross section area on the heat leak, temperature profile as well as the voltage drop of the leads. The multi-tube structure is adopted and improved for the leads. The results of numerical simulation using CFD software package Fluent6.0 for the multi-tube-structure leads are presented, which can be used to improve the design of the leads.
文摘It′s important that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting system conduction cooled by GM coolers. This paper presents an experimental investigation into the effects of pure Ag and AgAu alloys sheath materials on the properties of Bi(2223) multifilamentary tapes and the optimisation of conduction cooled hybrid current leads made from copper and Bi(2223)/Ag or Bi(2223)/AgAu tapes. The thermal conductivity of the tapes were measured by cryogenic steady heat flux method and the resistance was measured by using standard DC four probe method at low temperature. The results showed that the reduction of thermal conductivity by the addition of Au into the sheath material of Bi(2223) tapes was 65 0 0, 75 0 0 and 85 0 0 lower than that of pure Ag sheathed Bi(2223) tapes and the increase of resistivity was 4.9 , 10 and 19.4 times higher than that of pure Ag for the addition of 2.2 0 0, 5.7 0 0 and 10.7 0 0Au(atom ratio) respectively. And the study also attempts to optimise thermodynamically the conduction cooled hybrid current lead by using a developed model, which took the irreversibility of commercial GM coolers, the contact resistance and thermal conductance into account. Predictions from the model showed that AgAu alloys were suitable candidate materials to replace Ag as sheath material of Bi(2223) tapes applied in HTS current leads. In addition, Bi(2223)/AgAu was a suitable material to be applied as the HTS section of hybrid current leads in conduction cooled superconducting electric systems.
基金supported by the Author of National Excellent Doctoral Dissertation of China (No.20050053)Analysis and Measurement Research Fund(2007-21) of Kunming University of Science and Technology
文摘The α-PbO2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO2 electrodes. The physic- ochemical properties of the α-PbO2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry （LSV） and A.C. impedance. A compact and uniform layer of lead dioxide ：）vas obtained at the current density of 3 mA.cm-2. A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO2. The corrosion resistance of α-PbO2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities in aqueous Zn2＋ 50 g·L^-1, H2SO4 150 When used as anodes for oxygen evolution g·L^-1, the Al/conductive coating/α-PbO2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA·cm^-2. The lowest roughnest factor was obtained at 1 mA·cm^-2.
基金supported by ITER IO, the National "973" Program of China (No. 2007ID2006)the National ITER Special Support for R&D on Science and Technology for ITER, CN Schedule Task (No. 2008GB102000)
文摘An experimental Paschen test setup has been established to analyze the quality of ITER current lead （CL） insulation and extend the research on Paschen＇s law under various conditions. Insulation problems can destroy a machine if a Paschen discharge is triggered by an insulation defect that is caused by faulty manufacturing, electromagnetic force, and thermal stress load with a certain degree of vacuum helium or pipe leakage. The results show that the CL insulation mock-up worked well under normal temperature and pressure. Besides, the mock-up also worked well in helium conditions and at 80 K temperature at different pressures. One area of CL insulation was severely destroyed when the 80 K test was conducted after 5 thermal cycles, resulting in Paschen discharge phenomenon. The breakdown voltage is maintained at a relatively low level under different pressure conditions; the change of breakdown voltage was mainly due to the change of pressure, and such change was in line with the Paschen law.
文摘The possibility of using Pb-electroplated reticulated SiC as the positive current collector for lead-acid batteries was investigated. Reticulated SiC with two aperture sizes (3 and 2mm) were tested as the substrate of positive electrode. It was found that the reticulated SiC has an excellent corrosion resistance in H2SO4 solution, and the Pb layer electroplated on reticulated SiC showed analogous electrochemical behavior to metal Pb. Preliminary test of the battery performance indicated that the utilization efficiency of the positive active mass of new designed batteries are improved compared with the conventional batteries. The improvement could be ascribed to the high specific surface area of the reticulated structured positive current collector, which was further supported by the even better performance of the battery made from a smaller aperture size (2mm) reticulated SiC as the substrate of the positive electrode.
文摘PTC热敏陶瓷的无铅化是绿色智能加热及电路智能保护元件研制的重要前提。为了获得可在空气气氛下烧结且兼具高居里温度和高升阻比的无铅化PTC热敏陶瓷,本工作采用固相法制备了(1-x)BaTiO_(3)-0.5 x Bi_(0.5)Na_(0.5)TiO_(3)-0.5 x Bi_(0.5)K_(0.5)TiO_(3)和0.98BaTiO_(3)-0.02 y Bi0.5 Na_(0.5)TiO_(3)-0.02(1-y)Bi_(0.5)K_(0.5)TiO_(3)三元固溶体系无铅PTC热敏陶瓷材料,研究了不同含量的Na和K元素对无铅PTC热敏陶瓷材料的烧结特性和电学性能的影响。结果表明,BNT和BKT均与BaTiO_(3)形成固溶体,随着BNT含量的增加,PTC陶瓷平均晶粒尺寸减小,当BNT和BKT含量相同时,PTC陶瓷可以在较宽的烧结温度范围内实现半导化,且在空气气氛下烧结温度为1200℃的陶瓷样品具有最佳的PTC效应,其室温电阻率为128Ω·cm,升阻比为5个数量级,居里温度为142℃。
