Faculty Profiles - UEDA Hiroshi

Position control of active magnetic levitation using sphere-shaped HTS bulk for inertial nuclear fusion

K. Suga, K. Riku, K. Agatsuma, H. Ueda, A. Ishiyama

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 ( 16-35.37-38 ) 2008

Language：English Publisher：IOP PUBLISHING LTD

We have developed an active magnetic levitation system that comprises a field-cooled disk-shaped or sphere-shaped HTS bulk and multiple ring-shaped electromagnets. In this system, the levitation height of HTS bulk can be controlled by adjusting the operating current of each electromagnet individually. Further, the application of the vertical noncontact levitation system is expected due to its levitation stability without mechanical supports. We assume that this system is applied to inertial nuclear fusion. However, one of the important issues is to achieve position control with high accuracy of the fusion fuel in order to illuminate the target evenly over the entire surface. Therefore, this system is applied to the levitation and position control of a sphere-shaped superconducting capsule containing nuclear fusion fuel. In this study, we designed and constructed a position control system for the sphere-shaped HTS bulk with a diameter of 5 mm by using numerical simulation based on hybrid finite element and boundary element analysis. We then carried out the experiment of levitation height and position control characteristics of the HTS bulk in this system. With regard to position control, accuracies within 59 mu m are obtained.

DOI： 10.1088/1742-6596/97/1/012162

Fatigue tests of YBCO coated conductors

S. Bamba, Y. Tanaka, T. Ando, H. Ueda, A. Ishiyama, Y. Yamada, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 2008

Language：English Publisher：IOP PUBLISHING LTD

In this paper, we report the fatigue characteristics of IBAD/PLD YBCO coated conductors. A YBCO coated conductor used in the superconducting coil of a SMES system is repeatedly subjected to mechanical tensile or compressive strain due to the Lorentz force during electrical charging or discharging. The superconducting characteristic of this conductor may deteriorate because of this cyclic strain. Therefore, it is necessary to investigate the effect of cyclic strain on the superconducting characteristics of YBCO coated conductors that have a laminated structure. We developed an experimental apparatus with a U-shaped sample holder in order to apply cyclic strain to the sample tape. This apparatus was used to perform the fatigue tests on YBCO coated conductors in liquid nitrogen in the absence of an external magnetic field. The strain cycles with the maximum strain epsilon(max) (zero external strain -> epsilon(max) -> zero external strain) were applied and repeated up to 5000 times, and the I-c measurements were performed at epsilon(max). Therefore, the application of cyclic strain with emax ranging from 0.3% to 0.5% did not result in any significant deterioration of the superconducting characteristics of the conductor.

DOI： 10.1088/1742-6596/97/1/012170

Visualization of Normal-zone initiation and Propagation using Fluorescent Paints

A. Ishiyama, H. Murakami, M. Tsuchiya, H. Ueda, H. Kato, K. Nara, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 ( 18-34 ) 2008

Language：English Publisher：IOP PUBLISHING LTD

To establish a stability criterion for Yttrium barium copper oxide (YBCO)-coated conductors, it is necessary to clarify their transient thermal characteristics. Thermocouple thermometers, resistance thermometers, or the relation between the temperature and resistance of the stabilizer used for the conductors are generally employed for measuring their temperatures. However, these methods can only be employed to observe fixed-point data. Hence, it is difficult to observe the longitudinal and transversal distributions of temperatures in coated conductors. In this study, we adopt a method for the visualization of the temperature distribution of coated conductors by using fluorescent paints whose color changes with temperature. By adopting this method, we can measure the two-dimensional distribution of temperature in magnetic fields and at cryogenic temperatures. Therefore, local heat generation in the YBCO tapes can be observed with a higher spatial resolution and the uniformity in the critical current density of YBCO tapes can be identified. In this paper, we describe the developed thermal visualization system and the preliminary experimental results of the visualization of normal-zone initiation and propagation in YBCO sample strips. Further, we also report a part of the normal-zone initiation and propagation mechanism by electromagnetic field and heat transfer analyses by employing a three-dimensional finite element method (FEM).

DOI： 10.1088/1742-6596/97/1/012169

Visualization of Normal-zone initiation and Propagation using Fluorescent Paints

A. Ishiyama, H. Murakami, M. Tsuchiya, H. Ueda, H. Kato, K. Nara, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 12169 2008

Language：English Publisher：IOP PUBLISHING LTD

DOI： 10.1088/1742-6596/97/1/012169

Degradation of YBCO Coated Conductors Caused by Over-current Pulses

X. Wang, H. Ueda, A. Ishiyama, Y. Iijima, T. Saitoh, N. Kashima, M. Mori, T. Watanabe, S. Nagaya, T. Katoh, T. Machi, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 2008

Language：English Publisher：IOP PUBLISHING LTD

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications because they have excellent J(c) characteristics at high temperatures and in high magnetic fields. For application to electric power devices such as transmission cables, transformers, and fault current limiters, the YBCO tapes might be subjected to a short-circuit fault current that is 10-30 times the normal operating current. In a worst-case scenario, YBCO tapes may degrade and burn. Therefore, it is important to clarify the mechanism of the degradation caused by an over-current pulse. This paper describes the experimental results of the degradation of the YBCO tapes through a series of over-current pulse tests. We focussed on the degradation temperature and carried out the experiments with different bending strains. Measurements were performed as a function of the amplitude of an over-current pulse for an operating temperature of 80 K (Gifford-McMahon cryocooler was adopted) in a self-field. We also examined a tape after the experiments with magneto-optical (MO) imaging, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction patterns.

DOI： 10.1088/1742-6596/97/1/012150

Degradation of YBCO Coated Conductors Caused by Over-current Pulses

X. Wang, H. Ueda, A. Ishiyama, Y. Iijima, T. Saitoh, N. Kashima, M. Mori, T. Watanabe, S. Nagaya, T. Katoh, T. Machi, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 12150 2008

Language：English Publisher：IOP PUBLISHING LTD

DOI： 10.1088/1742-6596/97/1/012150

Numerical simulation of critical current degradation of Nb<inf>3</inf>Sn strand in CIC conductor

Murakami, H., Ishiyama, A., Ueda, H., Koizumi, N., Okuno, K.

IEEE Transactions on Applied Superconductivity 18 ( 2 ) 1051 - 1054 2008

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The critical current of the ITER model coil degraded with an increase in the electromagnetic force. Experiments in which a periodic transverse load was artificially applied to a single coil strand showed this degradation. However, since these experiments were carried out under a certain condition, a general relation between the transverse load and the critical current was not obtained. Therefore, we have developed a numerical simulation code to investigate this general relation. The results of the numerical simulations are in good agreement with the experiments. This indicates that our numerical code is valid for the evaluation of the critical current performance of strands in CIC conductor. Next, the general dependence of the critical current degradation on Ta barrier thickness and resistivity of bronze was evaluated by using the developed simulation code. The results of the calculation showed that the Ta barrier thickness affects the critical current characteristics because of the large flexural rigidity of Ta barrier. On the other hand, the resistivity of bronze and the twist pitch of the filament rarely affect the critical current degradation since current transfers between filaments do not occur within the practical resistivity range of bronze.

DOI： 10.1109/TASC.2008.921979

Over-current characteristics of superconducting model cable using YBCO coated conductors

Ishiyama, A., Wang, X., Ueda, H., Yagi, M., Mukoyama, S., Kashima, N., Nagaya, S., Shiohara, Y.

Physica C: Superconductivity and its Applications 468 ( 15-20 ) 2041 - 2045 2008

Language：English Publisher：ELSEVIER SCIENCE BV

For the application to power transmission cables, a number of YBCO tapes would be assembled and wound in spiral on a Cu-former. YBCO tapes and the Cu-former are connected in parallel and they might be subjected to short-circuit fault currents 10-30 times the operating current. In this study, we constructed a 1 m long YBCO model cable. Over-current with a peak of 31.5 kArms and a duration of 2.0 s, which was established by JEC (Japanese Electrotechnical Committee), was applied to this cable in a liquid nitrogen bath. The redistribution of the transport current between YBCO tapes and the Cu-former were examined by using Hall sensors. The numerical simulations were carried out using a newly developed computer program based on the 3D finite element method (FEM) in order to clarify the over-current characteristics in the cable. From the comparison of the experimental and simulation results, the validity of the developed computer program was confirmed. Therefore, we performed the simulations of a 10 m long model cable when carrying a fault current of 31.5 kArms applied for a durations of 2.0 s, and also estimated the influence of the cross-section area of the Cu-former and the Cu shield layer on the thermal behavior of the model cable by using the developed computer program. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2008.05.276

Fatigue tests of YBCO coated conductors

S. Bamba, Y. Tanaka, T. Ando, H. Ueda, A. Ishiyama, Y. Yamada, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 12170 2008

Language：English Publisher：IOP PUBLISHING LTD

DOI： 10.1088/1742-6596/97/1/012170

Overcurrent Characteristics of 1 m Long Superconducting Model Cable using YBCO Coated Conductors

H. Ueda, X. Wang, A. Ishiyama, S. Mukoyama, M. Yagi, N. Kashima, S. Nagaya, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 ( 45-51 ) 2008

Language：English Publisher：IOP PUBLISHING LTD

In applications to power transmission cables, a number of YBCO tapes would be assembled and wound spirally on a Cu former. The YBCO tapes and the Cu former would be connected in parallel and could be subjected to short-circuit fault currents 10 to 30 times the operating current. The fault currents would drive the YBCO tapes into the normal state and thus generate Joule heating for the duration of the fault. Therefore, in order to examine the stability and feasibility of YBCO power transmission cables, it is important to demonstrate the redistribution of the transport current and the electromagnetic coupling between the YBCO tapes and the Cu former during a short-circuit fault current. We constructed a 1 m long superconducting model cable and subjected it to an overcurrent with a peak of 31.5 kA(rms) for a duration of 2.0 s, as established by JEC (Japanese Electrotechnical Committee), in a liquid nitrogen bath. We examined the redistribution of the transport current between the YBCO sample tapes and the Cu former by using Hall probes. In addition, we developed a novel computer code based on the finite element method and an equivalent circuit in order to clarify the characteristics of the redistribution of the transport current and the thermal behaviour within the cable. Finally, we designed a 10 m long cable that would reach the degradation temperature of the YBCO tape due to the fault currents.

DOI： 10.1088/1742-6596/97/1/012168

Overcurrent Characteristics of 1 m Long Superconducting Model Cable using YBCO Coated Conductors

H. Ueda, X. Wang, A. Ishiyama, S. Mukoyama, M. Yagi, N. Kashima, S. Nagaya, Y. Shiohara

8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07) 97 12168 2008

Language：English Publisher：IOP PUBLISHING LTD

DOI： 10.1088/1742-6596/97/1/012168