Guan, XiangZhang, ShuyueBian, XingChen, Huaiyu...
10页查看更多>>摘要：The damping characteristic of HTS magnetic levitation system is related to the stability of levitation, and it is an important research index for dynamics analysis. However, due to the complexity of the system structure and the strong nonlinearity of HTS, it is often difficult to solve the damping calculation model. Therefore, there are few reports on the quantitative research of system damping. In this paper, the damping mechanism of HTS magnetic levitation system is clarified macroscopically by using the method of energy analysis, and the calculation method of equivalent damping coefficient based on energy analysis is given, which is compared with the evaluation method based on traditional vibration theory. At the same time, we also verify the effectiveness of the scheme of controlling system damping through eddy current damper quantitatively, and preliminarily study the influence of setting damper on the HTS magnetic levitation bearing. The research work of this paper not only helps to understand the damping mechanism of HTS magnetic levitation system, but also lays a foundation for further dynamic modeling of the system.
原文链接:
NSTL
Elsevier
Kuznetsov, V. I.Trofimov, O. V.
10页查看更多>>摘要：We measured the rectification of an ac voltage in a structure of superconducting circularly-asymmetric aluminum rings in series, permeated with a magnetic flux and biased with a low-frequency alternating current (without a dc component). This rectification is due to the shift of the maxima of the critical currents of different polarity relative to the zero flux in opposite directions along the flux axis in the asymmetric ring. For the first time, we propose a model for a temperature-dependent phase shift equal to difference between dimensionless kinetic inductances of wide and narrow semirings having the same length and thickness. The shift is not zero in the case of different critical currents densities in both semirings. This is possible only in a situation of different critical temperatures of both semirings. The model describes well the temperature-dependent shift of the maxima of the critical currents, answers the long-standing mysterious challenge of the shift and removes extremely strange contradiction between the results of different measurements, previously found in circularly-asymmetric aluminum structures.
原文链接:- NSTL
- Elsevier
Akbar, AroojRiva, NicoloDutoit, Bertrand
8页查看更多>>摘要：A Mach-Zehnder Interferometer (MZI) based optical fibre sensing technique, developed and patented by EPFL, is an efficient and economical way to detect hotspots in High Temperature Superconductor (HTS) applications. Due to the MZI sensitivity being a composite of strain sensitive and temperature sensitive contributions, the MZI gives an instantaneous response to a quench (within 10 ms), because of the quick strain transfer to the optical fibre. However, the MZI output signal can also manifest the environmental noise caused by mechanical vibrations, bubbling in the cryostat and temperature variations, along with the response to the quench. This presents the problems of false alarms and indiscernible response to a quench. Discrete wavelet transform (DWT) has been proven to be a useful tool for feature extraction in different fields requiring signal categorization and hence holds the potential to enable quench recognition in the MZI output. This paper proposes an effective approach of performing DWT based feature extraction on experimental data and subsequently using the extracted features for the MZI response classification using two machine learning based classification techniques: k-nearest neighbours (KNN) and Artificial Neural Network (ANN). For this manuscript, experiments were performed using MZI for quench detection in an HTS tape. Feature extraction was then implemented on these experimental measurements using discrete wavelet coefficients extracted at different decomposition levels from the MZI output; these features were then used to train the KNN and ANN models for identifying quench in the MZI signal. This method could be a valuable supplement to the MZI technique by enabling the development of a real time application that can process the MZI output data as well as eliminate the occurrences of false alarms; thereby facilitating reliable quench detection. With this development, the MZI technique would become an even more attractive solution for the health monitoring of HTS applications.
原文链接:- NSTL
- Elsevier
Huang, XiaoyanMa, ShuoZhang, HongmeiLiu, De...
10页查看更多>>摘要：We investigate theoretically the nonlocal and local transport properties of relativistic electrons tunnelling through a silicene-based superconducting double-barrier sandwiched between two ferromagnets in the presence of an external electric field. Based on the Blonder-Tinkham-Klapwijk formalism, the crossed Andreev reflection (CAR), nonlocal, and local differential conductances are numerically calculated by using a transfer-matrix method. We find that the energy regions of both the exclusive elastic cotunneling and exclusive CAR processes are gradually broadened as the exchange splitting energy increases. The CAR, nonlocal, and local differential conductances have a symmetrical distribution with respect to the external electric field and the nonlocal transport process is suppressed when the superconducting gap is large enough. Furthermore, the CAR, nonlocal, and local differential conductances exhibit periodic oscillatory behavior by increasing either the superconducting or insulating barrier potential, along with typical quasiperiodic oscillations as the middle insulating barrier width increases.
原文链接:- NSTL
- Elsevier
Das, PayelGhosh, Ajay Kumar
4页查看更多>>摘要：Superfluid phase stiffness (SPS) of NCBCO superconductor as a function of T has been extracted by using the Ambegaokar-Halperin-Nelson-Siggia (AHNS) theory at the zero magnetic field. The Berezinskii-Kosterlitz-Thouless (BKT) phase transition temperature, T-BKT has been extracted to be 54.0 K. The idea of the vortex glass (VG) transition has been applied to the resistive states of the BKT phase transition observed at 54.0 K. We have extracted the static exponent required in the Fisher, Fisher and Huse (FFH) scaling equation. The scaling of the current-voltage (IV) curves around 54.0 K with and without finite SPS is possible within the framework of the FFH theory.
原文链接:- NSTL
- Elsevier
Wang, Qing-YuSun, Liang-TingZhao, Hong-WeiZhou, You-He...
11页查看更多>>摘要：Thermomagnetic instabilities are widely observed in bulk superconductors and superconducting (SC) films in form of flux jumps and flux avalanches. Recent experiments demonstrate that the frequent flux jumps can also be observed in superconducting coils. These undesirable flux jumps have a significant impact on coils. However, it is much more difficult to simulate the flux jumps in superconducting coils than bulk superconductors because of the unacceptable number of elements for such complex structures with composite materials. In this paper, we develop a possible scheme to numerically simulate the flux jumps inside the superconducting coils with acceptable computation resources, which allows us to qualitatively study the main characteristics of the thermomagnetic instabilities. Furthermore, we explore the sensitivity of flux jumps inside the superconducting solenoid to various electromagnetic and thermal parameters as well as the ramp rate. Our scheme of numerical simulation may pave an appropriate way to further study the thermomagnetic instabilities inside the various superconducting coils with complex structures.
原文链接:- NSTL
- Elsevier
Wang, JiaJunLi, LiLiang, YaoTao, HuaLong...
4页查看更多>>摘要：Electronic structure and structural stability of (Ba(0.75)Ae(0.25))Fe2As2 (Ae = Li, Na and Rb) have been studied by first principles calculations. After the introduction of Ae atoms, the magnetic moment was reduced. The Ae atoms doping increased the number of carriers in BaFe2As2 and caused the movement of the Fermi level, which led to the reconstruction of Fermi surface. The calculated results of formation energy, Gibbs free energy and phonon dispersion showed that Ae atoms were not easily soluble in BaFe2As2. BaFe2As2 doped system was unstable after Ae atoms were introduced. With the increase of ion radius of introduced Ae atoms, the stability of doped system decreased and doping became more difficult.
原文链接:- NSTL
- Elsevier
