Critical current and ac susceptibility in superconducting tapes with elliptical cross-section

Recent progress in the development of methods used to predict AC loss in superconducting conductors is summarized. It is underlined that the loss is just one of the electromagnetic characteristics controlled by the time evolution of magnetic field and current distribution inside the conductor. Powerful methods for the simulation of magnetic flux penetration, like Brandt's method and the method of minimal magnetic energy variation, allow us to model the interaction of the conductor with an external magnetic field or a transport current, or with both of them. The case of a coincident action of AC field and AC transport current is of prime importance for practical applications. Numerical simulation methods allow us to expand the prediction range from simplified shapes like a (infinitely high) slab or (infinitely thin) strip to more realistic forms like strips with finite rectangular or elliptic cross-section. Another substantial feature of these methods is that the real composite structure containing an array of superconducting filaments can be taken into account. Also, the case of a ferromagnetic matrix can be considered, with the simulations showing a dramatic impact on the local field. In all these circumstances, it is possible to indicate how the AC loss can be reduced by a proper architecture of the composite. On the other hand, the multifilamentary arrangement brings about a presence of coupling currents and coupling loss. Simulation of this phenomenon requires 3D formulation with corresponding growth of the problem complexity and computation time.

Section: Ac-ac Case For a Wire With A Rectangular Cross-sectionsupporting

confidence: 53%

Predicting AC loss in practical superconductors

Gömöry

Šouc

Vojenčiak

et al. 2006

“…In contrast to the transport ac loss, for which the result for elliptical bars is very simple, there is no analytical solution to the transverse magnetization curve available for an elliptical bar, so that one has to make numerical calculations for every value of b/a. Some partial results of such calculations have been published in [8,9]. The present work is a continuation of [8,9] by calculating the transverse critical-state complex susceptibility of an elliptical bar as a function of the field amplitude and b/a, in parallel to the work done for rectangular bars in [7].…”

Section: Introductionmentioning

confidence: 97%

“…Some partial results of such calculations have been published in [8,9]. The present work is a continuation of [8,9] by calculating the transverse critical-state complex susceptibility of an elliptical bar as a function of the field amplitude and b/a, in parallel to the work done for rectangular bars in [7].…”

Section: Introductionmentioning

confidence: 97%

Transverse ac susceptibility of superconducting bars with elliptical cross-section and constant critical-current density

Chen

Pardo

Sanchez

2005

Self Cite

The complex ac susceptibility χ = χ − jχ of an infinitely long hard superconducting bar with an elliptical cross-section of semi-axes a and b is numerically calculated with a uniform ac field applied along the b axis, based on the critical-state model with a constant J c . Normalized to the exact low-field limit of −χ , χ 0 , −χ and χ as functions of the field amplitude H m normalized to the exact full penetration field H p are given in tables and figures for 0.01 b/a 100. It is shown for any value of b/a that, with increasing H m /H p , χ is proportional to and inversely proportional to H m at H m /H p 1 and 1, respectively. Defining a characteristic point as where χ takes its maximum χ m , it is shown that, with increasing b/a, χ m /χ 0 increases from 0.188 to 0.229, whereas H m (χ m )/H p increases from 0.35 to 1.18 and −χ (χ m )/χ 0 displays a minimum at b/a ≈ 0.5. The results are used for comparing with some experimental data of a mono-filamentary Bi-2223/Ag tape.

“…In the model of the elliptical strip an analytical expression of this type cannot be found. However, in the work [6] the authors managed to find a simple expression,…”

Section: The J C Determinationmentioning

confidence: 99%

Contactlessj_cdetermination and magnetic coupling in multifilament Bi-2223/Ag tapes

Seiler¹,

Gömöry²,

Fabbricatore³

et al. 2004

Self Cite

In the contactless determination of critical current density in a DC or AC magnetization experiment, the use of an appropriate assumption about the field and current distribution in the sample is of key importance. While there exist generally accepted theoretical models describing the flux penetration into some simple shapes such as the slab, strip or disc, the case of composite tape containing many superconducting filaments in a metallic matrix is far from being completely understood. We compare the values of the critical current density obtained from transport measurements and the values evaluated from the AC susceptibility data for two Bi-2223/Ag multifilament tapes of different filament architecture. In one tape the filaments form two columns; in the other they are arranged in an overlapping pattern. The pattern of flux penetration into the two filamentary structures is examined and its consequences for the critical current density evaluation from the AC susceptibility measured in the perpendicular geometry are presented. As a result, the typical dimension to consider in the critical state induced by external magnetic field is the thickness of the column of filaments in the case of the columnar tape, and the thickness of an individual filament in the case of the tape with overlapping filaments.