Simple technique for superconducting joints quality estimation in bulk melt-processed high temperature superconductors

We propose an empirical approach to estimate the quality of superconducting joints (welds) between blocks of bulk high temperature superconductors (HTS). As a measuring value, we introduce a joint's quality factor and show its natural correlation with joint's critical current density. Being simple and non-destructive, this approach is considered to be quite important to solve the problem of utilization of HTS in large scale applications. The approach has been applied to characterize the joint's quality of melt-processed Y-123 joined by Tm-123 solder.Comment: 3 pages with 2 figures (revtex

Temperature dependence of trapped magnetic field in MgB2 bulk superconductor

Based on DC magnetization measurements, the temperature dependencies of the trapped magnetic field have been calculated for two MgB2 samples prepared by two different techniques: the high-pressure sintering and the hot pressing. Experimentally measured trapped field values for the first sample coincide remarkably well with calculated ones in the whole temperature range. This proves, from one side, the validity of the introduced calculation approach, and demonstrates, from another side, the great prospects of the hot pressing technology for large scale superconducting applications of the MgB2.Comment: 3 pages, 3 figures, submitted to AP

Thermobaric Effect on Melt-Textured MBa2_2Cu3_3O7−δ_{7-\delta} (M = Y, Nd)

The effect of a short (10-30 min) thermobaric action (in the 1-5 GPa pressure and 700-1300$^\circ$C temperature range) on the structure, superconductive and mechanical properties of melt-textured-MBa$_2$Cu$_3$O$_{7-\delta}$ (M=Y, Nd) or MT-MBCO have been studied. The existence has been established of pressure-temperature--time conditions (2 GPa, 800$^\circ$C for 30 min and 900-950$^\circ$C for 15 min for MT-YBCO; 5 GPa, 850-900$^\circ$C for 15 min for MT-NdBCO) the treatment under which allows superconductive properties of the materials (because of the contact with zirconia and high pressure) to be preserved or improved, mechanical characteristics increased and the materials condensed.Comment: 2 pages (tex), 2 figures (eps), to be presented at LT2

Superconducting joining of melt-textured Y-Ba-Cu-O bulk material

The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO parts. The peculiarities of solidification, phase formation, structure transformations and electromagnetic properties of MT-YBCO soldered with TmBa2Cu3O7-d are discussed.Comment: PS of 6 pages text and 5 figures, presented at ICMC'2000, Brasi

Substitution induced pinning in MgB_2 superconductor doped with SiC nano-particles

By doping MgB_2 superconductor with SiC nano-particles, we have successfully introduced pinning sites directly into the crystal lattice of MgB_2 grains (intra-grain pinning). It became possible due to the combination of counter-balanced Si and C co-substitution for B, leading to a large number of intra-granular dislocations and the dispersed nano-size impurities induced by the substitution. The magnetic field dependence of the critical current density was significantly improved in a wide temperature range, whereas the transition temperature in the sample MgB_2(SiC)_x having x = 0.34, the highest doping level prepared, dropped only by 2.6 K.Comment: 4 pages, 6 figure

MgB₂-based superconductors for fault current limiters

A promising solution of the fault current problem in power systems is the application of fast-operating nonlinear superconducting fault current limiters (SFCLs) with the capability of rapidly increasing their impedance, and thus limiting high fault currents. We report the results of experiments with models of inductive (transformer type) SFCLs based on the ring-shaped bulk MgB2 prepared under high quasihydrostatic pressure (2 GPa) and by hot pressing technique (30 MPa). It was shown that the SFCLs meet the main requirements to fault current limiters: they possess low impedance in the nominal regime of the protected circuit and can fast increase their impedance limiting both the transient and the steady-state fault currents. The study of quenching currents of MgB2 rings (SFCL activation current) and AC losses in the rings shows that the quenching current density and critical current density determined from AC losses can be 10-20 times less than the critical current determined from the magnetization experiments