Comparative study of mono- and multi-filamentary MgB2 wires with different boron powders and malic acid addition
KIM Jung Ho （NIMS ）； DOU Shi Xue （Wollongong 大）； RINDFLEISHI Matt, TOMSIC Mike （Hyper Tech Research）； KUMAKURA Hiroaki （NIMS ）
KIM.Jungho*nims.go.jp
Abstract:We evaluated the effects of malic acid addition and different boron powders with semi-crystalline and amorphous phases on the critical current density of MgB2 wires. We found that critical current density of wires made from amorphous boron showed better performance. This is due to full reaction between Mg and B powders even at low temperature of around 650oC. It also keeps the small grain size， which leads to a strong flux pinning. From transmission electron microscopy （TEM） observations， semi-crystalline boron powders had Beta-rhombohedral structure as a main phase. Interestingly， both powders had a lot of defects such as twin， dislocation， and stacking fault powders inside. These probably can cause a partial reaction between starting powders， resulting in depression of the critical current density. For malic acid doped wires， critical current density of wire made from amorphous boron was estimated to 25，000 Acm-2 at 10 T and 4.2 K. This value is comparable to Nb-Ti of low temperature superconductor. This performance is the best presented so far in in-situ processed MgB2 wires.