•Even transverse voltage (ETV) appears at superconducting transition of the Nb–Ti tape near Hc2.•The features of the ETV change along the tape.•There is a strong dependence of the ETV on the ...excitation current.•When changing the geometry of the experiment from a perpendicular geometry (field directed normally) to the geometry when the field is in the plane of the tape, there is no significant change in the ETV.•The ETV is not described within the framework of the usual understanding of the resistivity appearance as the vortices movement.
We have measured both longitudinal and transverse voltages with respect to current in flat samples of superconducting cold-worked and heat-treated Nb-50wt%Ti tapes. In the vicinity of the Hc2 a transverse voltage is even with respect to the magnetic field inversion. We have found that transverse voltage varies significantly along the sample and depended on the magnitude of exciting current. Moreover, the behavior of the transverse voltage was qualitatively similar for two different orientations of applied field: in the plane of the tape and normal to the tape. The obtained data not only suggest that the main cause of the transverse voltage is material inhomogeneity, but also indicate that the transverse voltage is not described within the framework of the usual understanding of the resistivity appearance as the vortices movement.
•A brief overview of models predicting guiding angles is given.•The guiding effect has been experimentally studied depending on the magnetic field magnitude and the excitation current on the Nb-Ti ...tape with rarefied α-Ti particles – strong pinning centers.•The experimental data and models are compared. The model that describes the experiment most accurately is chosen.•It is shown that the guiding experiments can serve as a tool to distinguish between plastic and elastic flux flow modes.This article provides a brief overview of existing models that describe the guided flux motion phenomenon. The first model was proposed by Niessen et al. This original model utilizes the single-vortex approximation and provides a qualitative explanation of the effect; however, in most cases it provides an overestimated guiding angle. A second stochastic model explains the experimentally observed guiding angle decreasing (so-called “slipping effect”) by the influence of thermal fluctuations. However, the performed estimations show that thermal fluctuations should not be significant. Another model for predicting the guiding angle is the anisotropic pinning model. This model operates in the critical state approximation, and the slipping effect is the combined action of anisotropic pinning and vortex interaction. The predictions of all three models were experimentally tested on a wide superconducting Nb-Ti tape containing 6% by volume ratio of α-Ti particles that act as strong pinning centers. The number of samples was sliced at different angles to the rolling direction to control the driving force direction with respect to the principal material directions. The transverse and longitudinal components of the electrical field were measured simultaneously in a perpendicular magnetic field with increasing transport current. It was found that when the generated electric field was sufficiently small, the guiding angle varied significantly at different locations along the sample. In this case, the anisotropic pinning model predicted the guiding angle averaged over the sample length. With a further increase in the transport current (and driving force), the guiding angle became uniform along the sample.
Abstract
Various applications of superconducting materials require accounting of the critical current anisotropy relative to magnetic field direction -
I
c
7(θ). However, today there is no ...sufficiently comprehensive model that takes into account the anisotropy, therefore the angular dependences are usually not analysed, but only described using various mathematical formulas. As a result, the fitting parameters have no physical meaning and it is difficult to correlate the picture with the features of the microstructure. In this paper, we propose a method for analysing the critical current angular dependences based on the anisotropic pinning model. The applicability of this model for conventional superconducting Nb-Ti tapes with one peak in the
I
c
7(θ) dependence is shown. The possibility of extending this model to analyse the angular dependences of HTS materials is discussed.
The article presents a brief generalization of our recent experiments confirming that "irreversibility field" in Nb-Ti superconducting tapes is determined by the inhomogeneity of superconducting ...properties. It is shown that the effect is a direct consequence of the so-called δl-pinning, i.e. pinning caused by local reduction of the electrons mean free path. Based on the understanding of the irreversibility field nature, an assessment of the individual pinning force is performed. Good agreement is obtained with the estimations performed in the framework of the Larkin-Ovchinnikov pinning model (LO), which is valid for magnetic field less than the irreversibility field. The competing model is considered which is also valid for field range below the irreversibility field - the anisotropic pinning model (APM). The comparison of the fundamental length scales introduced in the LO and APM models is given.
Neutron stress diffractometry is used to study internal (residual) stress in a tape made of the AISI 310S stainless steel with a thickness of 100 μm and a width of 4 mm in three directions (along, ...across, and perpendicularly to the rolling plane). The residual macrostresses averaged over the tape length are determined at a segment of 40 cm. The macrostress distribution indicates a crescent-type deformation of the tape (bending in the rolling plane along the rolling direction). The correlation between macrostresses and internal microstresses is established (the stronger macrostresses, the higher concentration of the microstresses).
The main task in creating high-current cables based on HTSC-2 wires for thermonuclear installations is to maximize the resistance of the cable to mechanical stresses. Its solution is directly related ...to the strength of the HTSC-2 wires, which is determined by the supporting steel tape substrate. Therefore, the diagnosis of stresses in the carrier tape is of particular importance. The only direct method for measuring internal strains and residual stresses inside a material is neutron stress diffractometry. However, its application to thin steel tapes is limited by the intensity of the neutron beam. In this study, by the example of a 100-µm-thick AISI 310S stainless steel tape applied as a substrate in manufacturing HTSC-2 wire at the National Research Center Kurchatov Institute, it is shown that this restriction can be circumvented if the measurements are carried out on stacks of tapes similar to HTSC stacks in high-current cables. In this approach, the diagnosis with neutron stress diffractometry is performed on the AISI 310S tape as delivered, after mechanical polishing, and after applying a YSZ buffer layer. The high sensitivity of the method is noted, which makes it possible to determine the crescent-shaped deformation of the tape and the degree of its stretching after mechanical polishing and to measure the residual stresses arising during the deposition of the YSZ layer. The results obtained show that the neutron stress diffractometry has good prospects for diagnosing internal strains and stresses in HTSC stacks of high-current cables.
Magnetization curves measured with the Vibrating-Sample Magnetometer (VSM) are presented for narrow (2 × 11 mm typical) rectangular samples sliced from superconducting Nb-Ti cold-rolled tape with ...high pinning anisotropy. There are two types of samples: sliced along (RD) and across (TD) to the rolling direction. An anomalous shift of the magnetization central peak was found for TD-samples and not observed for RD-samples. This central peak shift is opposite in sign to the known one, which is usually observed in bulk materials. The Magneto-Optical Imaging (MOI) pictures suggest a possible mechanism for such an anomalous shift. From the longitudinal side, the magnetic flux penetrates into the tape relatively evenly, in accordance with the predictions of the critical state model. However, it is not true for flux penetration from the transverse side of the sample. Instead, the flux forms a dendritic structure oriented primarily along the rolling direction. The existence of such a structure leads to a drastic change in total magnetization around zero external fields, depending on the orientation of the rolling direction to the long side of the sample.
The superconducting magnetic system (SMS) project is proposed. The second-generation high-temperature superconducting tapes for SMS are developed, fabricated and tested in NRC “Kurchatov Institute.” ...The magnet will be manufactured from non-insulated double pancake coils. Such a double pancake coil is manufactured and tested in liquid nitrogen. The integral radial resistance of this coil is determined.
The article discusses the problem of determining electrical parameters of superconducting coils with bare windings. Procedures for measuring these parameters are described; in particular, inductance ...was measured by the voltage of a linear current input at a given rate. Although it is demonstrated to be impossible to determine inductance in a winding with a bare superconductor in the normal state, the inductance of a winding is comparable to that of an insulated wire in a superconducting state at currents below the critical value. The results of measuring the inductance, radial resistance, static current-voltage and magnetic characteristics of two tape coils with bare superconducting windings, one of which had a soldered connection, are presented. The insulated and bare superconducting winding parameters were compared and measurement conditions for the latter were formulated. The results of the study are applicable to the design and operation of superconducting devices with bare windings, such as coils, magnetic storage devices, stator windings of electric machines, etc.
Determination of No-Insulation HTS Coil Parameters Sychugov, V. V.; Guryev, V. V.; Krasnoperov, E. P. ...
IEEE transactions on applied superconductivity,
2022-June, 2022-6-00, Letnik:
32, Številka:
4
Journal Article
Recenzirano
A procedure for measuring the parameters of superconducting coils with non-insulated tape windings is described. The results of measurements of inductance, radial resistance, static current-voltage, ...and magnetic characteristics of two superconducting coils, one of which has a soldered connection, are presented.
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