Coupling losses and transverse resistivity of multifilament YBCO coated superconductors

TL;DR

This study investigates magnetization and coupling losses in filamentary YBCO coated conductors, revealing that laser ablation may create electrical contacts between filaments and substrate, affecting transverse resistivity.

Contribution

It introduces a method to separate coupling and hysteresis losses in YBCO conductors and compares transverse resistivity measurements from loss data and four-point tests.

Findings

Coupling loss can be isolated by frequency dependence analysis.

Laser ablation may cause electrical contact between filaments and substrate.

Transverse resistivity is close to substrate resistivity.

Abstract

We studied the magnetization losses of four different types of filamentary YBCO coated conductors. A 10 mm wide YBCO coated conductor was subdivided into 20 filaments by laser cutting. The separation of coupling loss from the total is possible because the energy loss per cycle in samples with electrically insulated filaments has a very small frequency dependence. We measured the frequency dependence of the total losses in the frequency range between 0.1 Hz and 500 Hz. The coupling loss was obtained from the total by subtracting the hysteresis loss. The latter was measured at low frequencies since only hysteresis loss is non-negligible at frequencies below 1 Hz. The transverse resistivity was determined from the coupling losses; it was assumed that the sample length is equal to half of the twist pitch. The values of transverse resistivity deduced from the loss data were compared with those obtained by the four-point measurements with current flowing perpendicular to the filaments. Preliminary results indicate that the current method of laser ablation creates electrical contacts between the superconducting filaments and the substrate. This was also confirmed by the Hall probe mapping of the magnetic field in the vicinity of the tape. The measured transverse resistivity was close to the resistivity of the substrate (Hastelloy).