Extracting the utmost from the high performance of Sm–Ba–Cu–O bulk superconductors by pulse field magnetization

Abstract

We have studied the magnetization of a melt-processed Sm–Ba–Cu–O bulk superconductor by magnetic pulses at 77 K. The amount of trapped magnetic flux (ΦT) as a function of the pulse amplitude exhibited a peak, which is attributable to the heating of the sample caused by the fast motion of flux lines in the presence of resistive forces. The peak value of ΦT was about half the amount of magnetic flux that was trapped when the sample was field cooled to 77 K, where the field-cooling (FC) value corresponds to the full capability of trapping magnetic flux by the sample. We found that sandwiching the sample with ferromagnetic materials and iteratively applying magnetic pulses while progressively decreasing the amplitude increases the amount of trapped magnetic flux. By combining these two techniques, ΦT increased to about 90% of that of FC magnetization.

Flux jump-assisted pulsed field magnetisation of high-Jcbulk high-temperature superconductors

“…The world record using PFM, using a modified multipulse, stepwise-cooling (MMPSC) technique, is only 5.2 Tesla at 29 K [18], which is much less than the true capability of these materials as indicated above. It should be noted that at higher operating temperatures (closer to T c , such as 77 K), fields have been trapped close to that of FC [7,[19][20][21][22]. So-called "giant flux leaps" have been observed by a number of research groups investigating PFM [7,18,[23][24][25][26], and more recently in unpublished experiments carried out in our own research group, where flux jumps occur in the superconductor, and magnetic flux suddenly intrudes into the centre of the superconductor, resulting in a large increase in the measured trapped field at the centre of the top surface of the bulk sample and full magnetization.…”

Trapped field properties of a Y–Ba–Cu–O bulk by pulsed field magnetization using a split coil inserted by iron yokes with various geometries and electromagnetic properties

“…In recent years, a ferromagnetic yoke has been inserted in the magnetizing fixture to increase the trapped magnetic field [12,13], in which permendur (50Fe+50Co alloy) and soft iron were used experimentally as a yoke material. We have also achieved a trapped field of over 3 T at 40 K on Gd-Ba-Cu-O disk bulk by PFM, employing a split coil with a pair of soft iron yokes [14], in which a symmetric trapped field profile can be also realized [15].…”

Local measurements of the magnetization process of bulk superconductors induced by a pulsed magnetic field

“…Most significantly, the difference in the trapped field with the FC method tends to escalate when the ability of trapping flux lines increases by improving the material characteristic or by decreasing the temperature. Therefore, many efforts have been devoted to overcome this problem and to increase the trapped field by the PFM method [7][8][9][10][11]. Fujishiro et al have achieved a record high trapped field of 5.2 T by PFM for a 46 mm diameter Gd-Ba-Cu-O bulk superconductor that was cooled by a cryogenic refrigerator, which is however still lower than the trapped field achieved by FC magnetization [11].…”