Characterization of In-Field Critical Currents in REBCO Tapes Over Wide Temperature Range by Pulsed Current Source With Supercapacitor
Yuji Tsuchiya, K. Mizuno, Yoshimitsu Kohama, Alexandre Zampa, Tatsunori Okada, Satoshi Awaji
Abstract
The field and temperature dependence of the critical current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is a vital factor in designing the superconducting magnets. The standard method of measuring <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> involves applying a dc current and measuring voltage. However, when assessing the field dependence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , the high magnetic field's space constraints and cooling power limit the injection of dc current into the sample. To address this, we have developed a method using pulsed current to significantly reduce heat generation. Our previous research reported an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurement system capable of handling up to 19 T and variable temperatures with a pulse current up to 500 A. In this study, we have enhanced the system with electric double layer capacitors, known as supercapacitors, allowing currents up to 2 kA. This upgrade enables the measurement of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in the high-temperature superconducting REBCO tapes, which are 4 mm wide, at cryogenic temperatures as low as 4.2 K in magnetic fields or 20 K even under a self-field. We have verified the system's reliability by comparing measurements of dc and pulsed currents. Additionally, we contrasted the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values of full width samples with those of samples containing micro-bridges.