Magnetic and Thermal Properties of HTS Bulk Magnet in the Pulsed-Field Magnetizing Process
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O R I G I N A L PA P E R
Magnetic and Thermal Properties of HTS Bulk Magnet in the Pulsed-Field Magnetizing Process T. Oka · D. Ishiduka · J. Ogawa · S. Fukui · T. Sato · K. Yokoyama · A. Murakami
Received: 2 November 2012 / Accepted: 3 December 2012 / Published online: 29 December 2012 © Springer Science+Business Media New York 2012
Abstract In order to enhance the field-trapping ability of high Tc superconducting melt-textured bulk materials which act as quasi-permanent magnets when they capture the external magnetic fields, it is important to enhance the mechanical toughness of the materials to stand the stress induced by the magnetic repulsive force and thermal expansion. We adopted a dense Dy123-based bulk material with reduced void concentration in the experiment. Since the heat generations due to the flux motions in the samples results in the degradation of Jc , the time evolutions of the trapped magnetic fields and the temperature rises during and after the pulsed-field magnetizing processes were precisely measured at the same time to evaluate the penetrating flux motions and the heat generations in the sample. A single and couple of the magnetic pulsed fields with various intensities were successively applied to the sample at 30 K. The single magnetic field application exhibited a peak effect in the trapped-field behavior and tended to decline due to the heat generation. In the iterative pulsed-field application, the behaviors of the trapped fields and the temperature changes were found to be inverse between the first and the second pulsed-field applications. This implies that the flux penetration behavior into the sample magnet at the second field application is strongly reT. Oka () · D. Ishiduka · J. Ogawa · S. Fukui · T. Sato Niigata University, 8050 Ikarashi-Ninicho, Nishi-ku, Niigata 950-2181, Japan e-mail: [email protected] K. Yokoyama Ashikaga Institute of Technology, 268-1 Ohmae-cho, Ashikaga, Tochigi 326-8558, Japan A. Murakami Ichinoseki National College of Technology, Takanashi, Hagisho, Ichinoseki 021-8511, Japan
stricted by the presence of former trapped fields which were formed by the first field applications. Keywords Pulsed field · Magnetizing · Trapped magnetic flux · Temperature rise · Bulk magnet
1 Introduction The melt-textured bulk superconducting compounds which include RE–Ba–Cu–O (RE = Y, Sm, Eu, Dy, Gd, abbreviated as RE123) and RE211 perform the excellent magnetic property as quasi-permanent magnets when they capture the applied magnetic fields [1, 2]. The maximum magnetic performance has reached 16 T at 24 K by doping Zn element, as reported by Gruss et al. [3]. The highest value of 17.24 T has been reported by Tomita et al. [4] by reinforcing Y123 bulk magnet by the resin impregnation technique. These data of the field-trapping ability are commonly achieved in the field cooling process (hereafter abbreviated as FC) with use of superconducting solenoid magnets. On the other, in the pulsed-field magnetizing process (PFM), one knows that the flux motion in the sample caus
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