YBCO Rods Research Articles

10.1007/s11455-008-1002-1

A new method is proposed for growing Y1Ba2Cu3O7−δ (YBCO) rods and special growth regimes are described which provide decreasing losses in these rods in the superconducting state. It is shown that the thermocapillary mechanism of liquid phase transfer during the melting and crystallization of YBCO is responsible for the formation of a nonsuperconducting phase at the boundaries between crystal blocks. Results of the measurement of current-voltage characteristics of YBCO rods in the superconducting state are presented.

Determining the absolute thermo emfs of conductors using a Y1Ba2Cu3O7 − δ rod

The voltage drop on a 110-mm-long Y1Ba2Cu3O7 − δ (YBCO) rod with a diameter of 7 mm bearing a current of 1 A has been studied as a function of the temperature. It is shown that YBCO rods can be used to measure the absolute thermo emf of conductors in a range of temperatures up to the onset of breakage of the superconducting state. The thermo emf of Ni, Cu, and W conductors was determined.

Decreasing losses in Y1Ba2Cu3O7−δ rods in the superconducting state

A new method is proposed for growing Y1Ba2Cu3O7−δ (YBCO) rods and special growth regimes are described which provide decreasing losses in these rods in the superconducting state. It is shown that the thermocapillary mechanism of liquid phase transfer during the melting and crystallization of YBCO is responsible for the formation of a nonsuperconducting phase at the boundaries between crystal blocks. Results of the measurement of current-voltage characteristics of YBCO rods in the superconducting state are presented.

Critical current properties in magnetic fields of YBCO superconducting rods prepared by unidirectional solidification method

We fabricated long length YBCO single domain superconducting rods of 150 mm in length by the unidirectional solidification method. From the observation of microstructures of the rod, it was confirmed that the volume fraction and size of Y211 phase crystals tend to increase with progress of unidirectional solidification. These phenomena could be explained by the pushing mechanism of the Y211 particles into the liquid phase by the growth interface and coarsening of Y211 particles in the liquid region. We have also confirmed the change of J c– B properties at the difference of the volume fraction and the morphology of Y211 phase crystals along the longitudinal direction. Using the middle regions of this YBCO rod, where the J c– B property is superior, we have fabricated the current leads supported with epoxy resin and FRP. We have obtained the critical current about 380 A at 77 K and 3 T where the ab-plane is in parallel to the applied magnetic fields. Additionally, we have also successfully supplied 1000 A current at 77 K and 3 T connecting the three current leads in parallel.

高温超電導電流リード 方向凝固材料を用いた電流リード開発

The development of a current leads using YBCO superconducting rods was reviewed. The textured YBCO rods were fabricated by a zone-melt process. A high Ic value of 2,000 A was obtained by the structural control of texturing and pinning centers by Y211 particles. The highly textured structure was realized by the growth conditions of high G/R (G: Temperature Gradient and R: Growth Rate). The fine Y211 particles were obtained by the addition of the Pt powder to reduce a coarsening rate of Y211 in the liquid. The current leads were formed by the development of packaging technique for high mechanical strength and connection with the electrodes. Concerning the mechanical strength, no degradation of Ic performance due to a vibration of 15 G was achieved. Consequently, the current leads with not only high superconducting current but low thermal invasion and Joule heating was realized. It was confirmed that the total heat load could be suppressed to be 0.21 W/pair for 500 A where the high and low temperatures were controlled to be 80 and 20 K, respectively.

Evaluation of the invasion heat for the HTS current lead using YBCO

Current leads using high- T C superconductors (HTS current leads) are one of cryogenic key devices to assemble compact superconducting magnets such as applied for maglev trains etc. It is essential to evaluate effective thermal conductance through a HTS current lead package together with evaluating Joule heat and critical current for efficient design that has high current capacity and low heat invasion. We have designed the 500 A class HTS current lead package using a YBCO rod whose size is ∅ 3 × 30 mm, and developed an apparatus to measure its heat invasion. Temperature drop as a function of heat flow between the two ends of the package was measured by a conventional steady heat flow method. The quantity of heat invasion of the package under typical practical conditions, from 80 K hot end to 20 K cold end, was 163 mW. This value was simulated to the total value of 158 mW by counting contributions of all the component materials.

Unidirectional-solidification of Y–Ba–Cu–O/Ag superconducting rods

The stability of the solid/melt interface in silver-added YBCO superconducting rods prepared by the unidirectional-solidification method was investigated by comparison with monolithic YBCO rods. The influences of the silver addition on the growth interface morphology were discussed with considering the ability of the nucleation on the Y211 particles dispersed ahead of the growing interface. In addition, it was suggested that the optimization of the process parameters both the temperature gradients at the growing interface and the pulling rate was necessary to obtain single domain crystals.

A large scale approach of bulk HTS to the electric utility area

On the basis of a novel industrial-like YBCO seedless functional melt texture grain alignment process, various HTS devices for superconducting magnetic bearings (SMB) and high-current leads for transport and limiting purposes are fabricated. Critical shielding currents of 30 kA/cm/sup 2/ at 77 K are utilized to construct radial-passive magnetic bearings for 20 kg loads or to suspend and spin a O 4 cm rotor safely to 120000 rpm. Stiffnesses between 40 to 140 N/mm are measured. Multi-grain YBCO rods up to 20 cm length are tested for more than 6 kA/cm/sup 2/ transport currents. The connections to the copper braids are improved to less than 0.4 micro-ohm at 1000 Amperes and 77 K. The experiments show the practical potential of melt textured YBCO with macroscopic orientation of the grain structure for electric power purposes.

Melt-textured ceramic superconductors: Fast-melt/fast-quench process in a solar furnace

A texturizing method for ceramic superconductors involving a new way for rapid melting and quenching in a solar furnace is presented. The method involves rapid melting of a silver-doped YBCO rod suspended in an evacuated quartz tube at a temperature exceeding 2000°C followed by rapid quench on a silver mould. The sample obtained is melt-textured in a tube furnace. The melt-textured product exhibits high critical current density of the order of 104 A/cm2 in the field of 1 T at 50 K. This property is discussed in the framework of pinning centers introduced in our materials during the rapid melting and quenching process. Nonsuperconducting phases created during the quenching process serve as these pinning centers.

Directional solidification of YBCO rods for current lead applications

A directional solidification procedure for long rods of YBa 2CU 3O 7 - Y 2BaCuO 5 composites has been developed based on a vertical Birdgman-like configuration. Single domain rods up to 10 cm in length and a section of 0.15 cm 2 can be fabricated with inductive critical currents above 10 5 A/cm 2 at 77K and zero field as measured by means of a SQUID magnetometer. Transport critical currents have been measured at 77K with pulsed current up to 800A flowing at several angles from the a-b plane, and it is shown that no grain boundary limitations occur when supercurrent cross the a-b planes, in agreement with the observation of reduced concentration of microcracks. The applicability of these textured rods as current leads will be discussed.

Fundamental Characteristics of Differential Transformer Type Displacement Sensor Using a YBCO Superconductor

A displacement sensor was constructed using a YBCO superconductor. The sensor consisted of an excitation coil, a differential coil, and a superconducting YBCO rod. The inductance of the differential coil decreased as a result of perfect diamagnetism (the Meissner effect) when the YBCO rod entered the coil. The YBCO rod could be shifted by as much as ±12 mm in the center of the differential coil, along the axis of the rod, by moving the holder attached to the rod. The relationship between the output voltage of the differential coil and the displacement of the rod was measured using a lock-in amplifier. Experimental results indicate that the displacement sensor characteristics, including sensitivity, linearity, stability, frequency dependence, and absence of hysteresis, are satisfactory. Together with the above results, the electrical properties of the superconducting materials were also examined and compared with those of ferrite and soft iron.

ＹＢＣＯ超伝導体を用いた差動変圧器形変位センサの基礎特性

A displacement sensor is constructed using a YBCO superconductor. Its construction consists of an excitation coil, a differential coil, and a superconducting YBCO rod. The inductance of the differential coil decreases as a result of perfect diamagnetism (the Meissner effect) when the YBCO rod enters the coil. The YBCO rod can be shifted by as much as ±12 mm in the center of differential coil, along the axis of the rod by moving the holder attached to the rod. The relationship between the output voltage of the differential coil and the displacement of the rod is measured by a lock-in amplifier. Experimental results indicate that the displacement sensor has good characteristics. Among them are sensitivity, linearity, stability, frequency dependence, and nonhysteresis. Along with the above results, the electrical properties of the superconducting materials are also examined, comparing them with those of ferrite and soft iron.