Publication Details

Wang, X., Dou, S. X., Sumption, M., Lee, E. & Collings, E. (2002). Suppression of AC (hysteric) loss by magnetic shielding of MgB2/Fe superconductors: the pseudo-meissner effect. In B. Balachandran, D. Gubser & K. Hartwig (Eds.), Proceedings of the International Cryogenic Materials Conference- ICMC, 16-20 July 2001 (pp. 824-827). USA: American Institute of Physics.


The M-H loops of MgB2 materials in bulk sintered form, as well as for PIT wire and tape MgB2/Fe monofilamentary composites, have been measured at various temperatures. The influence of Fe on the M-H loops of the tape and wire are discussed. The normal Fe response is subtracted with the use of M-H loops taken above Tc and the remaining magnetization suppression of the MgB2 is described in terms of field shunting in the Fe "shield". The level of Fe shielding, both of regions outside of the sample from the MgB2, as well as the MgB2 from the outside is discussed, the latter is quantified in terms of a M. Using finite element analysis, M is calculated locally for the tape in both FO and EO field orientations (with the field perpendicular to and along the wide side of the tape, respectively) as well as for the wire sample. It is seen that this ^B effect can be phenomenologically modelled as a pseudo-Meissner effect. Direct measurements of hysteretic loss vs applied field sweep amplitude, Hm, give a pseudo-Meissner field, HPS1, of 2 kOe for the round wire sample in reasonable agreement with calculation. The hysteretic loss above HpSl (and below the penetration field) was found to fit well to an expression proportional to (H-HPS1)3. By comparing calculations with and without HpSl it was seen that the Fe sheath significantly reduced the hysteretic loss in externally applied fields for these MgB2/Fe composites.

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