HTS current lead have been prepared by the TFA-MOD processed YBCO tapes. A current lead unit is composed of 6 bundles stacked by 4 YBCO tapes, Cu end caps and a pair of stainless steel boards. The YBCO tape is 5 mm in width and around 130 μm in overall thickness. The YBCO superconducting layer with 1.5 μm is formed on oxide buffered layers on Hastelloy substrate tape. The critical current of 24 YBCO tapes ranges from 145 A to 166 A at 77 K and self-field. The YBCO current lead is assembled from the 4 current lead units in parallel. The transport current of 10 kA at 77 K was stably carried with no voltage generation on the YBCO tapes of the assembled current lead for 10 minutes. Rogowski coils were attached on 4 current lead units to evaluate current distribution of them. The current unbalance of 930 A occurred between 4 units at transport current of 10 kA.
MgB2 wires have been prepared by diffusion process in pure Mg metal tube. Amorphous B powder mixed with 5 mol% SiC nano-sized powder and 10 mol% MgH2 powder was encased in a Mg tube, and then the tube was inserted into a pure iron tube to form the Fe/Mg/B(powder) composite wires. The composite was drawn into around wires of 1.0 mm in diameter without intermediate annealing. The composite wires were heat treated at 630℃ for 5 h in Ar gas atmosphere. Some of the specimens were hot-pressed under 10 MPa during heat treatment. The MgB2 core was synthesized through the diffusion reaction between outer Mg metal tube and inner B powder. MgB2 core with no MgH2 addition forms denser structure without voids and cracks in comparison with MgH2 powder addition. The Ic values at 4.2 K for the hot-pressed MgB2 wire of no MgH2 addition and MgH2 addition were 79 A and 34.5 A at 6 T, which correspond to the Jc of 1151 A/mm2 and 377 A/mm2, respectively.
The shapes of classic guitars are strongly governed by the sensibilities of the craftsmen who make them, and thus, shapes vary widely. Unlike violins and other instruments, no ideal shape has yet been established for guitars. In our research, we conducted a frequency spectral analysis of tone quality with the aim of manufacturing a guitar with enhanced tone quality. In this study, we examined the effects of varying sound hole diameter of guitar, and quantitatively identified the optimal diameter.