Evidence that transverse variability of critical current density can greatly mitigate screening current stress in high field REBCO magnets.

Plastic damage of REBCO (REBaCuO, where RE=rare earth) coated conductors by screening current stress (SCS) is a significant concern for ultra-high-field superconducting magnets. Indeed, the third Little Big Coil (LBC3), a REBCO magnet that generated a record, high field of 45.5 T, showed wavy plastic damage produced by excess SCS in all pancakes except two made with single-slit conductors having their slit edges pointing inward towards the magnet center.

The prospects of high-temperature superconductors.

Overcoming cost barriers could make high-temperature superconductors pervasive.

Origin of the enhanced NbSn performance by combined Hf and Ta doping.

In recent years there has been an increasing effort in improving the performance of NbSn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (H and H, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties.

Effect of heat treatments on superconducting properties and connectivity in K-doped BaFeAs.

Fe-based superconductors and in particular K-doped BaFeAs (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density (J) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In this work we investigated the properties of high-purity, carefully processed, K-Ba122 samples synthesized with two separate heat treatments at various temperatures between 600 and 825 °C.

45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet.

Strong magnetic fields are required in many fields, such as medicine (magnetic resonance imaging), pharmacy (nuclear magnetic resonance), particle accelerators (such as the Large Hadron Collider) and fusion devices (for example, the International Thermonuclear Experimental Reactor, ITER), as well as for other diverse scientific and industrial uses. For almost two decades, 45 tesla has been the highest achievable direct-current (d.c.

Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density NbSn Superconductor Wires.

To meet critical current density, J , targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of NbSn must be improved, but champion J values have remained static for the last 10 years. Making the A15 phase stoichiometric and enhancing the upper critical field H by Ti or Ta dopants are the standard strategies for enhancing high field performance but detailed recent studies show that even the best modern wires have broad composition ranges. To assess whether further improvement might be possible, we employed Extended X-ray Absorption Fine Structure (EXAFS) to determine the lattice site location of dopants in modern high-performance NbSn strands with J values amongst the best so far achieved.

Effects of filament size on critical current density in overpressure processed Bi-2212 round wire.

BiSrCaCuO (Bi-2212) conductor is the only high temperature superconductor manufactured as a round wire and is a very promising conductor for very high field applications. One of the key design parameters of Bi-2212 wire is its filament size, which has been previously reported to affect the critical current density ( ) and ac losses. Work with 1 bar heat treatment showed that the optimal filament diameter was about 15 μm but it was not well understood at that time that gas bubbles were the main current limiting mechanism.

Development of a Persistent Superconducting Joint between Bi-2212/Ag-alloy Multifilamentary Round Wires.

Superconducting joints are one of the key components needed to make Ag-alloy clad BiSrCaCuO (Bi-2212) superconducting round wire (RW) successful for high-field, high-homogeneity magnet applications, especially for nuclear magnetic resonance (NMR) magnets in which persistent current mode (PCM) operation is highly desired. In this study, a procedure for fabricating superconducting joints between Bi-2212 round wires during coil reaction was developed. Melting temperatures of Bi-2212 powder with different amounts of Ag addition were investigated by differential thermal analysis (DTA) so as to provide information for selecting the proper joint matrix.

Facility implementation and comparative performance evaluation of probe-corrected TEM/STEM with Schottky and cold field emission illumination.

We report the installation and performance evaluation of a probe aberration-corrected high-resolution JEOL JEM-ARM200F transmission electron microscope (TEM). We provide details on construction of the room that enables us to obtain scanning transmission electron microscope (STEM) data without any evident distortions/noise from the external environment. The microscope routinely delivers expected performance.