YBCO/Ag boundary resistivity in YBCO tapes with metallic substrates

Abstract

The quality of the contact between a YBCO layer and the protective silver coating is an important parameter affecting the current transfer between YBCO and the normal metal. We studied experimentally the quality of this contact in 6 mm wide YBCO-coated conductor with a critical current of ∼60 A at 77 K. The measured current transfer length for the original sample of a YBCO-coated conductor covered by ∼3 µm thick silver and for the same sample additionally laminated by a 25 µm thin copper layer was 0.19 and 0.47 mm, respectively. The contact resistivity determined from these experiments was between 3.7 × 10 −11 and 7.0 × 10 −12 m 2 . A direct measurement of the resistance between two overlapped tapes soldered by indium yielded values between 2.5 × 10 −12 and 5 × 10 −12 m 2 . The boundary resistance and current transfer length are important parameters for the design of the optimal tape architecture for coils and windings, especially for stability issues.

Measurement of the Joint Resistance of Large-Current YBCO Conductors

“…Above this current; there appears a flux-flow resistance for Tap B. In this figure, the joint resistance is found at 98.7 nΩ and the contact resistivity is evaluated to be 42.5 nΩcm 2 taking account of the contacting area We note that the presently obtained contact resistivity is close to the values evaluated by other authors such as presented in [15] that gives 30 nΩcm 2 For the 10-kA class sample with a soldered lap joint, Fig. 7 shows the measured joint voltage as a function of current.…”

Current sharing between superconducting film and normal metal

“…For W = 4 mm, this is equivalent to λ = 800 µm. For the value of λ ≈ 300 µm measured in [15], κW ≈ 13, so that the amount of power dissipation in the back side is smaller than that shown in Fig. 4(b).…”

Influence of the voltage taps position on the self-field DC and AC transport characterization of HTS superconducting tapes

“…The ratio between the current flowing in the normal metal and that flowing in the superconductor depends on the distance from the current lead and it is characterized by the so-called transfer length [1,14,15]. It was experimentally shown that this length is well below 1 mm for samples similar to ours [15]. To see details of the potential distribution along the length of the sample we made numerical simulations.…”