R&D efforts have been made for various applications of high temperature superconducting (HTS) conductors such as power cables, high field magnets and transformers. In Japan, a national project to develop materials and power applications using coated conductors was started in 2008. Since then, we have been fabricating coated conductors by pulsed laser deposition (PLD) for the development of a 5 kA, 66 kV class “3-in-One” HTS model cable system as a part of this project. In order to construct the HTS cable, stable production of coated conductors with high critical current density (Ic) is required. For this purpose, the deposition process of buffer and superconducting layers on the clad-type substrate are key technologies. We installed a 300 W high power excimer laser to our PLD equipment to obtain a thick superconducting layer. In addition, we improved the buffer layers to enhance the Ic property. Moreover, we used a wide tape of 30 mm to obtain large production throughput, and successfully obtained uniform superconducting characteristics across the tape width. As the Ic property of over 300 A/cm was confirmed for 100 m length, coated conductors have become promising for AC applications, especially for HTS cables aimed at lowering AC loss. In this study, we investigated the Ic values and stable manufacturing process of coated conductors by PLD process.
Differences in characteristics were also discussed according to the length of the tape.
As a result of R&D efforts for high Ic performance of a thick GdBCO layer and good Ic distribution across the width of 30 mm, the total amount of 10 mm width GdBCO conductors produced every month has reached 1 km.
Based on these production technologies, 3 km Clad-PLD conductors with 10 mm width were fabricated on the 30 mm substrates.The GdBCO layer was 2.1 microns and the target Ic value was 200 A/cm.
When the Ic value is over 200 A/cm, the yield becomes 34%. This data confirms that the stable production process has been achieved for GdBCO conductors with a satisfactory Ic value and piece length for HTS model cable.
Source: SEI TECHNICAL REVIEW ( N 73, October 2011)