Conjugate two-dimensional electric potential maps

Two dimensional electric potential maps based on voltage detection in conducting paper are common practice in many physics courses in college. Most frequently, students work on `capacitor-like' geometries with current flowing between two opposite electrodes. A `topographical' investigation across the embedding medium (map of equipotential curves) allows to reassure a number of physical properties. This paper focuses on some less common configurations that bear pedagogical interest. We analyze `open-geometries' with electrodes in the form of long strips with slits. They provide a natural groundwork to bring the student to complex variable methods. Aided by this, we show that shaping the conducting paper board one may analyze finite size effects, as well as some meaningful discontinuities in the measured potential. The concept of conjugate electric potentials is exploited. Equipotentials and electric field lines acquire interchangeable roles and may be obtained in complementary `dual' experiments. A feasible theoretical analysis based on introductory complex variables and standardized numerics gives a remarkable quantification of the experimental results.Comment: 15 pages, 8 figure

Smooth double critical state theory for type-II superconductors

Several aspects of the general theory for the critical states of a vortex lattice and the magnetic flux dynamics in type-II superconductors are examined by a direct variational optimisation method and widespread physical principles. Our method allows to unify a number of conventional models describing the complex vortex configurations in the critical state regime. Special attention is given to the discussion of the relation between the flux-line cutting mechanism and the depinning threshold limitation. This is done by using a smooth double critical state concept which incorporates the so-called isotropic, elliptical, T and CT models as well-defined limits of our general treatment. Starting from different initial configurations for a superconducting slab in a 3D magnetic field, we show that the predictions of the theory range from the collapse to zero of transverse magnetic moments in the isotropic model, to nearly force free configurations in which paramagnetic values can arbitrarily increase with the applied field for magnetically anisotropic current voltage laws. Noteworthily, the differences between the several model predictions are minimal for the low applied field regime.</div

Strong Localization of the Density of Power Losses in Type-II Superconducting Wires

A round straight superconducting wire has been used as numerical prototype for pursuing a comprehensive study on the local distribution of current and the density of power losses, attained by the simultaneous action of an ac transport current and an oscillating transverse magnetic field. The numerical simulations have been performed within the quasi-steady approach of the critical state theory, including virgin and premagnetized wires. A wide variety of shapes for the flux fronts characterizing the local dynamics of the electromagnetic quantities across the section of the wire has been revealed. Under special conditions, flux fronts characterized either by the so-called “field-like”, or “current-like ” shapes are shown, with the occurrence of multiple domains of current flow detached by thin lines acting as boundaries between the critical values Ic and - Ic . Despite the lack of symmetry for attaining at least an intuitive definition of the shape of the flux front, a universal pattern of the distribution of magnetic flux density has been identified. Also, a strong asymmetric localization of the density of power losses has been envisaged, as long as synchronous electromagnetic excitations are used.</div

IR laser line scanning treatments to improve levitation forces in MgTi0.06B2 bulk materials

Martinez, Elena/0000-0003-4839-5286; de la Fuente, German Francisco/0000-0002-0500-1745; Ozturk, Kemal/0000-0002-8847-1880; GUNER, SAIT BARIS/0000-0001-7487-4817; Celik, Sukru/0000-0002-6918-7569WOS: 000487657000015Infrared (IR) laser-line scanning has been widely used to induce different surface microstructures in a broad range of materials. in this work, this laser configuration was applied on the surface of MgTi0.06B2 bulk samples in order to ascertain its effects on their superconducting properties, particularly on the magnetic levitation forces. the microstructural changes produced by this type of laser treatment were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). It was observed that the thermal treatment induced by the laser improves grain connectivity in a layer of material just below the irradiated surface, in agreement with the observed improvement in critical current density values, J(c), which were estimated from isothermal magnetic hysteresis loops. A significant increment of both vertical (F-z) and lateral (F-x) magnetic levitation forces was achieved. Numerical calculations were performed to understand the experimental behaviour and to clarify how an improvement of J(c) near the surface can improve the magnetic levitation force of these materials. in addition, the same studies were carried out in similar bulk samples but with nano-sized silver particle additions of 3 and 6 wt %, in the outer ring of the bulk, observing also an improvement of the levitation forces, albeit less than in samples without Ag because of the better performance of the original samples after laser treatment. These results are relevant to those studying superconductor fabrication and material fabrication modelling, essential for the development of technological applications of superconductors, and are based on microstructure control via application of a recently developed laser-line scan method. (C) 2019 Elsevier B.V. All rights reserved.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [2219]; Spanish Agencia Estatal de Investigacion [ENE2017-83669-C4-1-R]; European FEDER ProgramEuropean Union (EU) [ENE2017-83669-C4-1-R]; Gobierno de Aragon "Construyendo Europa desde Aragon" [T54_17R]As authors, we would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK with program code 2219), the Spanish Agencia Estatal de Investigacion and the European FEDER Program (project ENE2017-83669-C4-1-R), and the Gobierno de Aragon "Construyendo Europa desde Aragon" (research group T54_17R). Authors also would like to acknowledge the use of Servicio General de Apoyo a la Investigacion-SAI, Universidad de Zaragoza and Erzincan University in Turkey for microstructural characterization