Electromagnetic properties of REBaCuO superconducting tapes considered for magnets of fusion reactors

Highlights

• Electromagnetic properties of 21 superconducting tapes were studied by vibrating sample magnetometer and by transport current measurements.

• Engineering currents deduced from magnetic hysteresis loops measured at 10 K, 50 K, and 77 K were compared with direct transport experiments.

• The transport current anisotropy varied in dependence of the details of pinning structure and technology of the tapes.

• The tapes reflected to neutron irradiation in a different way, in dependence of magnetic field, temperature, and the tape’s pinning character.

Abstract

The RE-123 tapes represent the most advanced product in the field of high temperature superconductors, developed for transport of high electric currents. Although this product has already proceeded to the stage of industrial production, the variety in techniques employed by different manufacturers make the final products by far not identical. We studied electromagnetic properties of a series of 21 tapes from main global wire manufacturers. The tapes were tested by magnetic induction technique (vibrating sample magnetometer, VSM) and by a transport current measurements. The aim was to find the best candidates for superconducting coils for fusion reactors. Engineering currents were deduced from magnetic hysteresis loops measured by VSM at 10 K, 50 K, and 77 K. The data for 77 K were compared with the results of direct transport experiments done at the same temperature. Current transport experiments also provided information on the current anisotropy. The VSM tests were repeated after neutron irradiation of the tapes by neutron fluence of 2.12 × 10¹⁸ cm⁻². A significant enhancement of engineering currents was observed in magnetic fields above 0.5 T in all investigated tapes and temperatures. The enhancement, similarly as the engineering current, was roughly exponential function of temperature.

Introduction

A huge effort has been recently devoted worldwide to development of a new generation of high temperature epitaxial superconducting REBa₂Cu₃O_y (REBaCuO, RE-123, RE = rare earth, usually Y or Gd) tapes prepared on metallic substrates. RE-123 is characterized by rather high critical current density up to vicinity of the critical temperature (typically above 90 K) and by a high upper critical field. The critical currents are particularly high just in thin films. However, the current density rather quickly drops with increasing film thickness [1], [2], which goes against the need of rather thick tapes for transfer of high currents. The superconducting layers require a suitable adaptation to the substrate − several buffer layers properly textured need to be used [3]. All the endeavor has led to development of the “second generation”, “coated conductor” tapes offered nowadays by several manufacturers on the market, in lengths up to 1.5 km, allowing construction of high-field magnetic coils [4], [5], [6]. While the basic characteristics are usually provided by manufacturers, some special applications, like use in magnets for fusion reactors, where neutron irradiation acts [7], [8], require an extended characterization.

In the present paper we bring a survey of engineering currents reached in a series of 21 tapes from three manufacturers, tested by inductive and transport techniques. The angular dependence of transport currents is provided and the first results of our study of the effect of neutron irradiation on the currents are shown.