Interfilament Resistance at 77 K in Striated HTS Coated Conductors

Abstract

-Striating HTS coated conductor (CC) tapes into narrow filaments offers the possibility of reducing the tapes' magnetization losses without unreasonably decreasing their current-carrying capability. However, realizing well-separated striations presents technological challenges, especially if the number of filaments is large and/or if a thick layer of metallic stabilizer is present. In these situations, the filaments can be easily coupled and their effectiveness to reduce magnetization losses is strongly diminished or eliminated. While the onset of coupling is well visible from magnetization loss measurements, the actual path of the coupling current is unknown. In this contribution we present a systematic study of the transverse resistance in HTS CC samples in order to get a deeper understanding of those paths. The measured samples differ in terms of manufacturer (SuperPower and SuperOx), and presence and thickness of stabilizer material. In addition, oxidation is used as a means to increase the resistance between the filaments in non-stabilized samples. The results are interpreted with a chain network model. This work provides useful insights on the factors determining the transverse resistance in striated HTS CCs, thus indicating ways to improve the effectiveness of the striation process for AC loss reduction.

Topical Review: Multifilamentary coated conductors for ultra-high magnetic field applications

“…The authors reported good agreement with modeling of multiple current paths using a chain network model showing a strong dependence on filamentization process parameters (laser striation and post-oxygenation), barrier resistances, i.e. the horizontal resistance through the filament stack, and a dominating substrate current path [109]. The latter finding also matches well with the results obtained in [120].…”

“…It was reported by Yanagisawa in 2011 [66] that magnet coils with a smaller tape width of REBCO-CC, a larger inner diameter and a higher ratio of operating current to the coil critical current generate a smaller central screening field ratio. For completeness, it is noted that for multifilamentary CCs in general, Q total = Q hysteresis + Q coupling + Q eddy [109]. Some of the first examinations of filamentized YBCO CCs were performed by Carr and Oberly in 1999.…”

“…Additional circuit model approaches were presented in [109] and [124] who also studied the interfilament resistances of filamentized CCs at 77 K by measuring across various filament-to-filament setups. The authors reported good agreement with modeling of multiple current paths using a chain network model showing a strong dependence on filamentization process parameters (laser striation and post-oxygenation), barrier resistances, i.e.…”

Spark-Discharge Plasma as a Method to Produce Low AC Loss Multifilamentary (RE)Ba2Cu3 O7 Coated Conductors

“…Using the equivalent resistor model used in [4], [5], [8] and a resistivity of Hastelloy at 77 K of 1.24 µW.m [17] the barrier resistance, R b , was calculated. The barrier resistance was much greater than the Hastelloy, suggesting good separation, which should prevent significant coupling losses.…”

“…It has been demonstrated that dividing the tape into n narrower filaments can reduce the hysteretic loss by a factor of n [1]- [3]. Additionally, coupling losses, due to resistive current flow between filaments, can be reduced by increasing the resistive barriers between superconducting regions and ensuring their transposition [4], [5].…”