Analysis of the operational characteristics of a high-Tc superconducting power supply with the Bi-2223 pancake load

This paper presents the design and fabrication of a high-Tc superconducting (HTSC) power supply with the Bi-2223 pancake load, as well as its characteristics as determined through experiments. HTSC power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid, and a Bi-2223 pancake load. In this experiment, a 331-mH electromagnet and 0.8-A dc heater current were used, and 8.5 and 17 s were used for pumping periods, respectively. Mechanism of the superconducting switch is used for heater-trigger. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 0.6 A with 0.01-V electromagnet voltage.     

Analysis of the operational characteristics of a heater-triggertype high-Tc superconducting power supply

This paper deals with the design and fabrication of a heater-trigger type high-T_c superconducting (HTSC) power supply, and its characteristics has been analyzed through experiments. A heater-trigger HTSC power supply consists of two heaters, an electromagnet, and a YBCO superconducting bulk. In this experiment, a 0.6-T magnet and a 2.3-A dc heater current were used and 190 s and 380 s were used for the pumping period. In order to measure the pumping current with respect to the magnet flux changes, hall sensors were installed at the surface of the YBCO bulk and inside of an iron core. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping current has reached about 12 A. In computer simulation, the maximum pumping current of the system has been predicted to be about 13 A     

Superconducting magnet system containing Bi-2212/Ag Coil Generates 21.8 T at 1.8K

We fabricated a Bi-2212/Ag double stacked pancake coil of 13 mmØ) in inner bore and of 46.5 mmØ in outer diameter, by using Bi-2212/Ag tapes prepared by the combination of continuous dip-coating process and melt-solidification technique. This small superconducting magnet was used as an insert magnet of a conventional superconducting magnet system and tested at saturated superfluid helium temperature (～ 1.8K) in various bias fields. The generated field of Bi2212/Ag coil was 0.9 T, with I_c of 310 A(criterion 10^-13Ω·m), in the bias field of 20.9 T. Thus, this superconducting magnet system achieved generation of magnetic field of 21.8 T in the full superconducting state.     

Development of a Conduction-Cooled HTS SMES

A 35-kJ/7-kW conduction-cooled high-temperature superconductor (HTS) superconducting magnetic energy storage (SMES) is developed. This paper presents the configuration of the HTS SMES and a part of important test results. The magnet of the SMES is a solenoid-type coil made of Bi-2223/Ag tapes, and cooled to about 20 K by conduction-cooled method. The SMES is assembled in the Electric Power System Dynamic Simulation Laboratory, Huazhong University of Science and Technology. A series of tests are successfully carried out to evaluate the performance of the SMES, including the current-carrying ability of the magnet, the active and reactive power exchange capability between the SMES and a simulated power system, as well as the power-compensating effect of the SMES to the simulated power system after short-circuit fault, etc.     

Temperature Dependence of Growth Mechanism for Nanoscale High T_c Superconductors

The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors （nano-YBCO）. A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy （TEM）. The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.     

Temperature Dependence of Growth Mechanism for Nanoscale High Tc Superconductors

The growth mechanisms of high temperature Yttrium-and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors (nano-YBCO). A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy (TEM). The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.     

Physical Effects of Mechanical Processes on Bi-2223 Tapes

The effects of intermediate mechanical deformation （IMD） and bending processing on Bi-2223 tapes were studied. Bi-2223 tapes were manufactured by powder-in-tube process with an IMD. Normal rolling （NR）, pressing （P） and sandwich rolling （SR） with different reduction rate were used in the IMD. And there were an optimum reduction rate existing for the three MID techniques, at which critical current reached maximum. Critical current densities Jc of Bi-2223 crystals were measured with an applied magnetic field B respectively parallel to ab face and c axis. Relations of Jc dependences of reduction rate and superconducting materials density D were respectively studied and showed a Gaussian distribution law. Maximum pinning force density Fmax and irreversible magnetic field Birr were introduced to describe the effects of mechanical processing. Analysis of experimental results showed that Jcs Fmax and Birr were linear dependence on D. Obviously, increasing D was a vital way to enhance Jc Bending experiments were performed for SR tapes sheathed by Ag and Ag/Sb and Ag/Mg alloy, respectively. Silver alloy sheathed tapes showed better bending properties than pure silver sheathed one. Therefore, silver alloy sheathed, optimum reduction rate of IMD, and increasing D for Bi-2223 tapes＇ applications were important technical strategies to enhance their mechanical, electrical, and magnetic properties.     

Fabrication of Ag-Sheathed Bi-2223 tapes using powders produced by aerosol spray pyrolysis

Bi-2223 tapes were manufactured from a fine “two-powder” product produced by using an aerosol spray pyrolysis technique. Critical current density of 22000 A/ cm2 at 77K and 0 T was achieved. Nondestructive transmission x-ray diffraction study indicated good alignment of the superconducting grains. The texturing process of the superconducting phase was found to be nearly complete after the first 24 h of heat treatment for the samples studied. Pressing was found to play little role in the texturing process. The texturing can be enhanced by Ag-doping. J_c, however, was not found to be improved significantly, presumably due to the reduced effective cross-sectional area. A new phase, Bi-4435, was identified which may play a significant role in the formation of 2223. On leave from Northeastern University, Shenyang, P.R.C. On leave from Kobe Steel Ltd., Kobe, Japan     

Ion beam switching magnet employing HTS coils

This paper describes the design, construction, and testing of an ion beam switching high-temperature superconducting (HTS) magnet installed at Institute of Geological and Nuclear Science (IGNS) in New Zealand. It was designed by a consortium comprising American Superconductor Corporation (ASC), ISYS, Applied Engineering Technologies (AET), the New Zealand Institute for Industrial Research and Development (IRL), and Alphatech. The work was also supported in part by New Zealand Foundation for Research and Technology-Technology for Business Growth Programme. The magnet generates 0.72 T in the airgap between two 410×700 mm warm iron poles. The Bi-2223 HTS coils are conduction-cooled with a single stage Gifford-McMahon (G-M) type cryocooler for steady-state operation. The magnet was fully tested at ASC during the fall of 1996. This represents the first large-scale fully operational HTS physics magnet announced so far. The successful operation of this magnet has verified maturation of HTS magnet technology employing conduction cooling techniques with G-M type cryocoolers. Long term operation of this magnet in continuous use will prove the reliability of HTS magnet systems in critical applications and is expected to open future opportunities for HTS in other related areas     

Fabrication and characteristics of tapes and test magnets made from Ag-Clad Bi-2223 superconductors

Pb_0.4Bi_1.8Sr₂Ca_2.2Cu₃O_x (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium, and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical current density (J_c) values>4×10⁴ A/cm² at 77K and 2×10⁵ A/cm² at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils. Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet generated significant self-field in background fields up to 20 T. The results are discussed in this paper.     

Development of Bi(Pb)-2223/Ag pancake-shaped and solenoidal coils

High temperature superconducting (HTSC) multifilamentary (MT) Bi(Pb)-2223/Ag tapes with reproducible critical current density of between 15000 and 20000 A/cm² at 77 K in self field have been achieved using the standard flat-rolling method as the intermediate deformation between sintering periods. Long lengths of Bi(Pb)-2223/Ag MT tapes up to 43 m prepared by the conventional method of powder-in-tube (PIT) have been successfully produced on a laboratory scale. Several coils have been fabricated from sections of the long length tape, using the co-wound wind-and-react (W&R) procedure for the pancake-shaped and the singly-wound W&R as well as R&W procedure for the solenoidal coils. A novel W&R solenoidal coil (reaching ~973 ampere-turns) wound on an alumina ceramic tube generates a DC field of ~19 mT at 77 K and has been fabricated together with five pancake-shaped coils, each generating an average of ~5 mT at 77 K. These are destined for magnet construction with a possible combined calculated field of ~0.04 T at 77 K (with liquid nitrogen as a coolant)     

Processing and transport properties of high-Jc silver-clad Bi-2223 tapes and coils

The powder-in-tube process has been used to fabricate long lengths of flexible, high-J_c, silver-clad Bi-2223 HTS conductors. By improving thermomechanical processing and precursor powder preparation, we have succeeded in achieving J_c values of≥4×10⁴ A/cm² at liquid nitrogen (77K) temperature and >10⁵ A/cm² at liquid helium (4.2K) and liquid neon (27K) temperatures in short tape samples. Detailed measurements with high applied magnetic fields are reported. Several long tapes up to 10 m in length have also been fabricated and cowound into small superconducting pancake coils by the “wind-and react” approach. Transport measurements at 77 and 4.2K for these coils are also reported.     

Fabrication of HTS dc Bias Coil for 35kV/90MVA SFCL

For a saturated iron core fault current limiter, superconductor is the only suitable material to make the dc bias coil, especially when the device is used in a high voltage power grid. Commonly, superconducting wires are used to wind the dc bias coil. Since the performance of the wires changes greatly under magnetic fields, the calculation of the field spatial distraction is essential to the optimization of the superconducting magnet. A superconducting coil with 141000 ampere-turns magnetizing capacity made of 17600 meters of BSCCO 2223 HTS tapes was fabricated. This coil was built for a 35kV/90MVA saturated iron-core fault current limiter. Computer simulations on magnetic field distribution were carried out to optimize the structural design, and experiments were done to verify the performance of the coil. The configuration and the key parameters of the coil will be reported in this paper.     

Fabrication of HTS dc Bias Coil for 35 kV/90 MVA SFCL

Abstract---For a saturated iron core fault current limiter, superconductor is the only suitable material to make the dc bias coil, especially when the device is used in a high voltage power grid. Commonly, superconducting wires are used to wind the dc bias coil Since the performance of the wires changes greatly under magnetic fields, the calculation of the field spatial distraction is essential to the optimization of the superconducting magnet. A superconducting coil with 141000 ampere-turns magnetizing capacity made of 17600 meters of BSCCO 2223 HTS tapes was fabricated. This coil was built for a 35 kV/90 MVA saturated iron-core fault current limiter. Computer simulations on magnetic field distribution were carried out to optimize the structural design, and experiments were done to verify the performance of the coil The configuration and the key parameters of the coil will be reported in this paper.     

Evaluation of the phase composition of BPSCCO bulk samples by XRD- and susceptibility analysis

This paper describes the comparison of the phase purity analysis, using XRD and AC-susceptibility measurements, on a number of BPSCCO samples, containing different ratios of the Bi-2212 and Bi-2223 phase. The differences observed in the results of both techniques were correlated with the growth mechanism of the Bi-2223 phase. The higher values for the percentage of the Bi-2223 phase observed in AC-susceptibility analysis, could be explained by the assumption that there is a specific distribution of the Bi-2212 and Bi-2223 phase during particle growth, resulting in shielding effects.     

Sandwich Roiling,Jc, and pinning energy in Ag-sheathed BPSCCO superconducting tapes

A “sandwich rolling” process was developed to prevent the formation of sausaging and cracks in the longitudinal direction. The stress-strain state of the tape in “sandwich” rolling is the same as that of uniaxial pressed tape because the deformation of steel sheets is negligible in comparison to that of Ag-clad tape. Critical current densities of 3.2 × 10⁴ A/cm² at 77K and 2.7 × 105 A/cm² at 4.2K and zero field Ag-sheathed Bi-based 2212 tapes have been achieved using a melt and atmosphere-controlled process. The comparison of pinning potential U₀(B) < U(T-0, B) for Bi-2212 tape and Bi-2223 tapes consisting of a different fraction of 2212 phase as well as Bi-2212 and Bi-2223 thin films shows that for the same fields, the U_o for good quality 2223 tapes is at least 1.3 times that for the best 2212 tape and epitaxial thin films after taking into account the difference of the T_c between 2223 tape and 2212 tape, indicating that in BSCCO compounds, in addition to anisotropy, the specific pinning centers such as dislocations, introduced during processing, affect the flux motion at lower B.     

A new MAGLEV system for magnetically levitated carrier system

A power-saving electromagnetic suspension system has been developed in which electromagnets with permanent magnets are used to suspend the vehicle. The electromagnets are controlled to maintain air gap length so that the attractive force by the permanent magnet always balances the total weight of the vehicle and its loads, based on modern control theory. This technology realizes a significantly power-saving system in which the electromagnetic coil current required to keep a vehicle levitating was extremely small, ideally zero. The 8-kg weight test vehicle with 4-kg load could be levitated continuously over 8 h, without recharging the on-board 1300-mAh batteries. This technology realized a completely contact-free material transportation system when combined with a contact-free driving system using linear motors. The attractive force characteristics of a permanent magnet with control electromagnets and the newly developed electromagnet control system that can eliminate power collecting devices from the electromagnetic suspension system are described     

Magnet cable technology development for high-temperature superconductor composite wire

Magnet cabling technology has been developed for Bi-based HTS composite wire. Concentric round cabling as well as Rutherford cabling has been proven in > 100 m lengths. For Bi-2223 precursor composite wire, post-cabling deformation is required to achieve high transport engineering current density (J_e), and early results have reached 5500 A/cm² at 77 K and self-field. Cable-and-deform conductor has similar magnetic field retention and anisotropy as conventional, nontransposed multifilament Bi-2223 composites with comparable J_e. HTS magnet cabled composites have great potential for providing high I_c, J_e, and reducing fabrication cost.     

Superconducting rectifier fluxpump for magnet system of the CMD-2detector

A superconducting rectifier fluxpump has been used for the dc power supply of the magnet system of the CMD-2 detector on the VEPP-2M collider at the Budker Institute of Nuclear Physics in Russia since 1989. The fluxpump provides a complete pumping cycle: charging the magnet system, stabilization of the magnetic field, and discharging. The fluxpump consists of an air-core current step-up superconducting transformer and two groups of thermally controlled superconducting switches arranged as a fullwave rectifier. Critical output current during the test was 5.4 kA. The accuracy of the field stabilization provided by the fluxpump is 2.5·10^-5. The fluxpump has exhibited reliable and safe operation during its entire history of use     

2 Tesla class magnet fabrication using Bi-2212 Ag-sheathed tape

Three test magnets of pancake-shaped coils using Bi-2212 tape were prepared by the wind-and-react technique. At liquid helium temperature, 16 pancake coils which were stacked in a volume of l4^Ø ×48^Øx 75^H mm generated a magnetic field of 2.25 Tesla (T), which was within 1% of the calculated B₀. The load lines of the magnet at every temperature from 4.2 to 30K coincided with the I_c of the short tape, up to the magnetic field of 6 T. For the quadruple pancake coil, the steady-state operational current, which produced increasing voltage with the lapse of time in a cryogenic atmosphere, was a value between the critical current (I_c) determined by the criteria of 1 ΜV/cm and l0^?13 Ω·m.