The design of a superconducting coil from high-performance REBCO coated conductors is often complicated because of complex anisotropy of the critical current density J_c . It is important to understand how much detail of this feature must be taken into consideration in the prediction of maximum achievable current and the expected ac loss. We present the results of investigation performed with a small (ten turns, 60 mm inner diameter) coil made from SuperPower tape of 12 mm width. The knowledge of J_c(B,θ) determined on short sample allowed prediction of the maximum achievable current of the coil and the ac loss behavior. We have also investigated the effect of the tape nonuniformity. Our results confirm that the lateral nonuniformity when J_c at tape edges is lower than in its center leads to significant increase of ac loss. A longitudinal nonuniformity, in particular a reduction of critical current in some portion along the tape length, is hardly observable in the ac loss result. On the other hand, using a piece of tape with lower J_c in the innermost coil turn would significantly reduce the maximum current. We also present calculations showing the change in current-voltage curve and redistribution of ac dissipation in the case of nonuniform tape quality.

Non-uniformity of superconductor properties, e.g. a critical current reduction close to the edge of a coated conductor (CC) tape could degrade its performance in some power applications. Reliable characterization of such non-uniformity and understanding of its mechanism requires investigation of the character and causes of degradation. In this paper spatial distribution of critical current density across the width of a CC tape is studied. Three different experimental methods allowing estimation of the local current density were utilized for this purpose: (i) magnetic field mapping above the tape through which a DC current is flowing, (ii) measurement of the critical current of separate strips prepared by patterning of the CC tape, and (iii) magnetization measurements of the pieces cut from various positions within the tape width. Very good agreement between the results obtained by these methods was found, showing a reduction of the critical current density at the tape edges with respect to its centre. Moreover, structural investigation by scanning electron microscopy revealed a correlation between the morphology and the critical current density across the tape width. Insertion of such real non-uniform distribution of critical current density into AC loss calculation resulted in a dramatic improvement in the agreement with experimental results.

Reliability is one of the crucial requirements of conductors used in resistive superconducting fault current limiters. Possible critical current degradation of a REBCO coated conductor during the limiter operation restrains broader application of devices based on these conductors. In this article the impact of an electrical stabilization layer on the conductor protection against overheating as well as its effect on electrical current evolution during the limitation period are investigated. For the experimental part of the study, a commercial copper stabilized REBCO coated conductor and a modified conductor without copper stabilization are compared. Extensive experimental work complemented by electro-thermal numerical modeling paved the way for studying the electrical and thermal effects separately. The numerical model assuming adiabatic conditions is sufficient to reproduce experimental results and predict the peak temperature for conductors with various stabilization layers in realistic conditions. Reduction of the conductor critical current caused by multiple current limitation pulses was studied using pulses with various durations. It was observed that the degradation due to temperature rise is gradual with the rate depending solely on the peak temperature. It is this quantity through which other parameters like the pulse duration, the thickness of stabilization and the peak current cause the tape damaging.

Damage behavior of two different metallization systems (Ti/Al bilayer and Ta-Si-N/Cu/Ta-Si-N multilayer) as finger electrodes in surface acoustic waves (SAW) devices was investigated. A special test structure was developed for this reason. The samples were loaded with traveling SAWs varying input power and loading time. Simultaneously during these experiments, the electric behavior of the SAW structure was measured and damage development by voids and hillock formation was observed using optical microscopy, too. The damaged structures were investigated by means of different microscopy techniques. Results show that the Cu-based metallization system has a significantly higher acoustomigration resistance and power durability in comparison with the Al thin film system.

The influences of stresses/strains on critical current, Ic in REBCO high temperature superconducting (HTS) tapes wound onto a round cable were investigated. Firstly, the HTS tapes were helically wound on copper tubes with various diameters in range of 2.95-8 mm, where considerably better results were achieved in case the superconductor layer of tape was positioned during winding at the inner side of the helix. The cables with tape wound on the tube with diameter of 6.35 mm were subjected to bending tests with various bending radii in range from 21 to 60.5 mm. The Ic degradation as a function of both, the tube diameter and bending radius has been studied by measuring current-voltage curve, from which the critical current was determined. The Ic degradation in all samples was confirmed by microstructural investigation of HTS layers using scanning electron microscopy.