IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 27, NO. 6, SEPTEMBER 2017 5900809 Influence of the Striation Process and the Thickness of the Cu-Stabilization on the AC Magnetization Loss of Striated REBCO Tape Aur´ elien Godfrin, Anna Kario, Roland Gyur´ aki, Eduard Demenˇ c´ ık, Rainer Nast, Juliane Scheiter, Alexey Mankevich, Alexander Molodyk, Wilfried Goldacker, and Francesco Grilli Abstract—Rare earth-based coated conductors have large ac magnetization losses, which hinder their use in a variety of ap- plications. A common way to reduce these losses is by striating the superconductor into narrow filaments by means of laser ablation. Practical superconductors also need a sufficiently thick copper sta- bilization. The best way of creating copper-stabilized filamentized coated conductors is still to be found. In this paper, the ac magneti- zation losses of differently prepared 12 mm wide coated conductors manufactured by SuperOx were measured. The samples differ in terms of thicknesses of copper stabilization (5 and 10 μm), num- ber of filaments (from 10 to 60), and order for copper deposition (filaments produced before or after electroplating the tape). The ac loss measurements were performed at 77 K in a wide range of fre- quencies of the external magnetic field, which allows determining the onset of coupling currents and the importance of the coupling losses. Complementary dc measurements of the transverse resistiv- ity between filaments help to understand the path of the coupling currents. Thanks to the variety of tested samples and operating conditions, this paper provides a direct comparison of the two striation processes in commercially available high-temperature su- perconductor coated conductors. Index Terms—AC loss measurement, ac magnetization losses, high-temperature superconductors, multifilamentary supercon- ductors, transverse resistivity. I. INTRODUCTION R ARE earth-based coated conductors (CCs) are currently regarded as the most promising high-temperature super- conductor tapes because of their high current carrying capability and good in-field behavior. For applications such as transform- ers and electrical machines, however, the dissipation caused by perpendicular ac magnetic fields is too large, and repre- sents a serious refrigeration burden. For example, the ac loss requirements for an all-superconducting generator operating at 500 Hz are discussed in [1]. Manuscript received November 4, 2016; revised March 9, 2017; accepted April 27, 2017. Date of publication June 26, 2017; date of current version July 21, 2017. This paper was recommended by Editor-in-Chief B. Plourde. (Corresponding author: Aur´ elien Godfrin.) A. Godfrin, A. Kario, R. Gyur´ aki, E. Demenˇ c´ ık, R. Nast, W. Goldacker, and F. Grilli are with the Institute for Technical Physics, Karlsruhe Institute of Technology, Karlsruhe 76344, Germany (e-mail: aurelien.godfrin@kit.edu). J. Scheiter is with the Department of Superconducting Materials, Leibniz Institute for Solid State and Materials Research, Dresden 01171, Germany. A. Mankevich and A. Molodyk are with SuperOx, Moscow 117246, Russia. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2017.2716820 A common approach to reduce the ac magnetization losses is by striating the tape into narrow filaments. The idea was originally proposed by Carr and Oberly in 1999 [2]. The results of the intense and widespread research carried on filamentization and reduction of the ac losses that followed have been recently summarized in a review article [3]. The most common process to realize the filamentized struc- ture is laser ablation. Its successful application to tapes with thick copper stabilization is, however, not straightforward [4] due to the difficulty of controlling the quality of the grooves and avoiding filament coupling [5]. In this contribution, we study the applicability of the laser ablation technique for producing copper-stabilized filamentized tape. In our previous work [6], significant ac magnetization losses reduction was observed for tapes with 5 μm thick copper stabilization. Here, we investigate the reduction of ac magneti- zation losses in CCs where the filaments are produced before or after the deposition of the copper layer (5 and 10 μm thick). Transverse resistance measurements and scanning electron mi- croscopy (SEM) photographs are used to interpret and support the results of ac loss measurements. II. SAMPLE PREPARATION All the tapes used in this work are 12 mm wide and were manufactured by SuperOx [7]. The filaments were created by means of a TRUMPF TruMicro 5025 laser. This laser has an infrared wavelength of 1030 nm, a pulse frequency of 400 kHz with pulse duration less than 10 ps, and a maximum power of 25 W with maximum pulse energy of 125 μJ. The typical width of the groove is 20 μm. More details about this striation technique can be found in [8]. The striations were produced at Karlsruhe Institute of Tech- nology (KIT) either before or after deposition of the copper layer. Throughout this paper, the two types of samples are iden- tified as striated before electroplating (SBE) and striated after electroplating (SAE), respectively. Samples with different thick- nesses of copper for the stabilization (5 and 10 μm) and different numbers of filaments (10, 20, 40, and 60) were produced. As it will be shown later, the actual thicknesses of the copper stabiliza- tion are different from the expected values due to the technical difficulties related to the electroplating technique. Nevertheless, for sake of clarity, throughout the manuscript we keep the the- oretical values of 5 and 10 μm for labeling the samples. 1051-8223 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.