The slit technique is an essential process for narrowing the second-generation high-temperature superconducting tapes (2G-HTS). It is still very challenging to eliminate edge defects introduced during slitting. In this work, we developed a set of reel-to-reel laser slit equipment for narrowing 2G-HTS tapes using a femtosecond infrared laser. In comparison with the commonly used mechanical slit (MS) technique, the laser slit (LS) technique produced no cracks at the tape edges. Electro-mechanical behaviors of 2G-HTS tapes with MS and LS edges were compared in liquid nitrogen conditions. The results of the uniaxial tensile tests showed only a minor difference in irreversible tensile stress/strain of the two kinds of tapes. However, uniaxial tensile fatigue tests showed that the critical current (Ic) retention of the LS tapes was about 14% higher than that of the MS tapes after 104 cycles (@ 77 K, σmax = 0.8σy, and a stress ratio of 0.1). Moreover, U-Spring compressive tests revealed that no irreversible Ic degradation occurred on the LS tapes under compressive strain up to -0.8%, with high reproducibility. On the contrary, the irreversible compressive strains of the MS tapes were rather scattered, ranging from -0.75% to -0.2%. Enhancement of electro-mechanical behaviors is strongly linked to fewer edge defects in the LS tapes. This research demonstrates significant advantages of the laser slit technique over the conventional mechanical slit technique, showing its promising prospects for demanding applications.

FeSe0.5Te0.5 coated conductor as a kind of 11-type iron-based superconductor is currently attracting much attention. Recently, the bare FeSe0.5Te0.5 coated conductor tapes were developed by Shanghai Jiao Tong university and verified their superconductivity. For the future application, the FeSe0.5Te0.5 tapes should be subjected to the high electromagnetic forces and stress-strain. In this study, the authors encapsulated the bare FeSe0.5Te0.5 coated conductor tapes with copper layers to enhance the mechanical performance. The reversible critical current performance of the bare and the copper encapsulated FeSe0.5Te0.5 tapes under uniaxial tensile strain was tested. The critical currents of two kinds of tapes were measured over a wide range of applied uniaxial tensile strain by the U-shaped bending spring, respectively. The results show the critical performance of the bare FeSe0.5Te0.5 tapes decreases linearly with respect to tensile strain. The copper encapsulated FeSe0.5Te0.5 tapes have better performance than the bare tapes, with an irreversible tensile strain limit of 0.15%. In addition, the actual irreversible tensile strain limit of the copper encapsulated FeSe0.5Te0.5 tapes reaches 0.29% after considering the influence of the cooling process.

Iron-based superconductors (IBS) have attracted intense interest from scientists around the world. The first FeSe0.5Te0.5 hybrid coil including one FeSe0.5Te0.5 single pancake coil (SPC) and eight YBCO double pancake coils (DPCs) was successfully fabricated and test in this study. The FeSe0.5Te0.5 tape used in the hybrid coil is encapsulated strengthen tape which is with 0.15 mm thickness and 10.5 mm width to withstand the high stress during the cold test. The FeSe0.5Te0.5 encapsulated tape exhibits good performance at 4.2 K cold test. YBCO DPCs were divided into two groups connected to both sides of the FeSe0.5Te0.5 SPC. The critical current of the FeSe0.5Te0.5 coil was measured under the background field increased from 0 T to 10 T. The transport critical current of the FeSe0.5Te0.5 SPC showed 108.1 A at self-field and 17.4 A at 10 T, which had almost the same performance as the short sample. The results in this study showed that the FeSe0.5Te0.5 coated conductor coil have good performance in high magnetic fields.

122-type iron-based superconductors (IBS) have attracted extensive attention due to their excellent performance. The 100-m class Ba1-xKxFe2As2 (Ba-122) 7-filamentary IBS tapes were successfully fabricated in Institute of Electrical Engineering, Chinese Academy of Sciences. This study has performed the tests of the 7-filamentary Ba-122 short tape samples (Bas samples) and the 100-m class 7-filamentary Ba-122 tape samples (Ba100 samples) under various kinds of strain by the U-shaped bending spring devices. Both types of samples were still reversible even when the applied compressive strain reached -0.65%. In addition, the reversible tensile strain limit of the Bas and Ba100 samples were 0.25% and 0.28%, which increased to 0.38% and 0.41% after considering the effect of the cooling process.