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ISSN: 2772-8307
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cited:1
Microwave surface resistance in MgB2: Effect of Te and cubic-BN addition on flux flow and pinning
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Article Number:Article 100170
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Abstract
Corresponding email:enrico.silva@uniroma3.it
MgB is a perspective superconductor for many power applications. How this potential refers also to microwave or radiofrequency applications is still to be determined. Although its ultimate surface resistance in zero field is not competitive with conventional metallic superconductors, its strong pinning properties can favor RF applications in a dc magnetic field. Nonetheless, the RF response in the vortex state has been relatively less studied, as well as the effect of artificial pinning centers on the microwave surface resistance in the mixed state. In this paper we study the surface resistance of spark-plasma-sintered MgB, with and without Te and cubic-BN (cBN) addition, in a dc magnetic field up to 1.2 T. We summarize previous results on pure MgB, and we present new data on Te- and cBN- added MgB. We use a two-tone dielectric-loaded resonator to measure the field-dependent surface resistance at 16.5 and 26.7 GHz in the temperature range from 10 K to . By exploiting the simultaneous measurements at two frequencies, we extract the flux-flow resistivity, the pinning constant and the depinning frequency . The two-band nature of MgB affects the field dependence of the flux-flow resistivity. The microscopic superconducting state is not affected by the addition of artificial pinning centers, indicating that Te and cBN do not affect interband or intraband scattering. Pinning shows a measurable trend towards an increase in the Te- and cBN- added samples at higher temperatures and fields. We finally compare the results to those obtained in bulk NbSn, also in view of possible in-field RF applications such as microwave cavity-based haloscopes.
cited:3
Rutherford MgB2 cable with 20 twisted filaments inside the Nb/CuNi/CuZn sheath
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Article Number:Article 100172
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Abstract
Corresponding email:Pavol.Kovac@savba.sk
A fine-filamentary CuZn sheathed MgB 2 wires produced by Hyper Tech Inc were used for 12 strand Rutherford cable of thickness 0.70–0.76 mm. Critical currents of short cable samples were measured at 4.2 K and external fields 4.0–8.0 T and also at temperatures 15–25 K and magnetic fields 1.0– 5.5 T. The threshold of engineering current density Acm −2 for the cable size of 0.72 mm 2.55 mm was obtained at field of 4.5 T and temperature 4.2 K and at 2.3 T for 20 K, respectively. Magnetization measurements of the cable with transposed strands and twisted filaments have shown reduced AC losses, but, the coupling currents loss contribution was still visible. AC losses measured for the same size Rutherford cable made of single-core wires demonstrate the effect of well decoupled filaments. Consequently, the cabling of thin single-core MgB 2 wires shows a promising way for low loss conductors suitable for AC applications.
Abstract
Corresponding email:mohammad.yazdani-asrami@glasgow.ac.uk
The utilization of superconductors in modern aviation, power and energy, space, healthcare, and quantum sectors offers substantial advantages, including significant energy savings, higher reliability, lower CO emissions, higher efficiencies, and increased power densities. However, the quench phenomenon – transition from superconducting state to normal state – presents a major challenge, particularly in high temperature superconductors (HTSs), and especially in sensitive applications including fusion energy and aviation sectors. Most of the existing quench detection systems, i.e., conventional techniques, simply work based on threshold, and therefore, they have challenges being inflexible, non-intelligent, slow, and with the potential of missing quench or raising false alarm. This study proposes an advanced quench diagnostic technique aiming at enhancing reliability of HTS devices. This diagnostic technique quantifies quench events by analyzing the ratio of a selected harmonic component’s amplitude, including the second to ninth harmonics, to that of the fundamental frequency in voltage measurement. Fast Fourier Transform (FFT) is employed to analyze the frequency-domain characteristics of voltage signals in both quench and non-quench stages. Amplitudes of the main harmonic frequencies were measured in the spectrum and calculated the harmonic amplitude ratio. Principal Component Analysis (PCA) was applied to reduce dimensionality and extract the most relevant features associated with quench events. The original 17 harmonic ratio features were transformed into three principal components per label, preserving essential information of the dataset for classification. The Support Vector Machine (SVM) was used as an automatic intelligent decision-making technique to discriminate new cases of quench from non-quench condition. Finally, after continuous optimization of the PCA and SVM model, this novel approach, based on experimental data, demonstrated to reach an accuracy of 100% and promised a fast, more flexible, and reliable method for quench diagnostics. In addition, to validate and demonstrate the generalizability of the proposed quench detection method, this diagnostic technique was tested for a totally new HTS coil sample with different type, configuration, and turns number, which high discrimination accuracy was observed. This is a real testimony to the effectiveness of the proposed technique which is robust and generalized. However, further tests on larger and more diverse datasets are underway to accelerate its future applicability in fusion, electric transportation, and renewable energy sectors.
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