AC susceptibility as a characterization tool for coated conductor tapes

Gömöry, Fedor; Vojenčiak, M; Solovyov, Mykola; Frolek, L.; Šouc, J; Seiler, E; Bauer, Markus; Falter, M.

doi:10.1088/1361-6668/aa858d

Cited by 7 publications

(2 citation statements)

References 114 publications

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“…This kind of nonuniformity plays an important role below I c when only a part of the superconductor is engaged in transporting the current. The deviation of AC loss from the prediction at low currents assuming a uniform j c is nicely explained by this effect, and an analysis of AC susceptibility can be used to deduce the nonuniform j c profile [39].…”

Section: Introductionmentioning

confidence: 89%

Impact of critical current fluctuations on the performance of a coated conductor tape

Gömöry

Šouc

Adámek

et al. 2019

Supercond. Sci. Technol.

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Coated conductor (CC) tapes often exhibit critical current, Ic, which fluctuates along the length coordinate, x, leading to an Ic(x) dependence. The need to reduce the price of these tapes does not favor a decrease in the variation of Ic in the near future. Therefore, it is reasonable to develop a method for estimating the possible impact of such fluctuating transport ability on the performance of superconducting devices. Fortunately, providing Ic(x) data together with the delivered conductor is becoming a standard approach among CC tape producers, and in-depth analysis of such data is now possible. Extrapolation of the short sample testing methodology to the case of a device incorporating many meters of CC tape leads to the introduction of an ‘overall critical current’ as a value generating 1 μV cm−1 of electric field over the whole conductor. We show that in the case of Ic(x) fluctuations obeying the Gaussian distribution one can predict the value of the overall critical current from the mean value and the variance of the Ic(x) data set. Deviation from the Gaussian distribution found in real tapes would cause a further reduction of the overall critical current. Conversely, in the case of strong dropouts in the critical current value, a statistical approach is useless and one must analyze the probability of the weakest location developing in a hot spot with a dramatic increase of temperature. Extending the analysis for a single tape to cables and coils results in a rather simple summary: when current sharing is possible, the reduction of overall critical current with respect to its mean value is significantly depressed. This favors the parallel arrangement of tapes with low contact resistance allowing current migration from tape to tape. On the other hand, the insulation of tapes leads to the same overall critical current reduction as observed for a single tape.

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Section: Introductionmentioning

confidence: 89%

Impact of critical current fluctuations on the performance of a coated conductor tape

Gömöry

Šouc

Adámek

et al. 2019

Supercond. Sci. Technol.

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“…The magnetization curve was measured in the calibration-free system [31] adapted for the magnetization loop recording [32], as shown in figure 5. The source of sine wave signal, with a frequency of 72 Hz, was the DSP lock-in amplifier 7265 from EG&G Instruments (Signal Recovery™).…”

Section: Ring From Superconducting Bulk Materialsmentioning

confidence: 99%

A–V formulation for numerical modelling of superconductor magnetization in true 3D geometry

Solovyov

Gömöry

2019

Supercond. Sci. Technol.

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We present the numerical procedure suitable for computing the distribution of electrical currents in a superconductor with geometry extending in all three spatial dimensions when it is exposed to a magnetic field changing in time. Its main advantage is that it solves the problem in terms of vector potential, of the magnetic field. Such an A-formulation is usually the default option for magnetic field calculations in commercial finite element codes. We have used it in the past when a two-dimensional (2D) approximation was found to be sufficient to predict AC losses of single wires, cables, and coils with circular turns. Incorporation of superconductor properties based on the critical state model is straightforward in 2D because the flow of current is restricted to one direction only. The main challenge in extending the method to three dimensions is to cope with the situation when currents could flow in any direction. We have found that assuming that the local current density in a superconductor is always parallel to the local electrical field, and that its modulus is limited by the critical current density, provides sufficient input for accomplishing a new working equation, linking the vector of current density to the time derivative of the magnetic vector potential. Our method successfully passed testing on the benchmark problem of superconducting cube magnetization. It is also used to interpret the magnetization measured on two cylindrical superconducting objects in the transverse field: one was a tube made from bulk BSCCO and the other a REBCO coated conductor tape helically wound on a non-metallic tube. Computed magnetization loops in both cases show good agreement with experiments and confirm the validity of the method.

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Investigation of Gamma-Induced Changes to Screening Currents and AC Losses in Mono- Versus Multi-filamentary REBCO Coated Conductors Using DC and AC Magnetometry

Campbell,

Sasaki,

Zhang

2024

J Supercond Nov Magn

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REBCO (rare-earth barium copper oxide) coated conductor tapes are a highly attractive option for magnet materials in future tokamak fusion power plants. However, the threat of intense neutron and gamma radiation, together with AC losses during magnet coil ramping, has raised concerns around magnet coil lifetimes. Irradiation-induced changes to flux creep rate has been identified as a key performance-limiting factor in REBCO tapes at low temperatures and high fields post-irradiation with gamma rays; spontaneous flux creep contributes to hysteretic AC loss in REBCO cables under applied AC fields. Knowing that multi-filamentary tapes are under consideration for tokamaks as an AC loss mitigation, magnetic measurements and gamma irradiation experiments are presented here on striated and mono-filamentary YBCO tapes to investigate the differences in post-irradiation screening currents and AC losses. Reduction in AC losses improved magnetisation critical current density (Jc) retention after 1 MGy in the multi- relative to the mono-filamentary samples. After the 5 MGy dose, striations then made the multi-filamentary tape more susceptible to Jc degradation because of the thinner individual filament width. Scanning transmission electron microscopy analysis on an analogous GdYBCO mono-filamentary tape did not indicate the introduction of nm-scale amorphisation to the active GdYBCO layer after gamma irradiation. A potential theoretical explanation for the underlying mechanism altering the flux-pinning landscape across the REBCO layer surface in gamma-irradiated tapes is discussed. This work concluded that gamma effects on screening current capability should be considered in future tokamak REBCO tape qualification studies.

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AC susceptibility as a characterization tool for coated conductor tapes

Cited by 7 publications

References 114 publications

Impact of critical current fluctuations on the performance of a coated conductor tape

Impact of critical current fluctuations on the performance of a coated conductor tape

A–V formulation for numerical modelling of superconductor magnetization in true 3D geometry

Investigation of Gamma-Induced Changes to Screening Currents and AC Losses in Mono- Versus Multi-filamentary REBCO Coated Conductors Using DC and AC Magnetometry

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