Monitoring of the Thermal Strain Distribution in CICCs During the Cyclic Loading Tests in SULTAN

Abstract

A technique to measure in situ the behavior of the magnetic susceptibility vs. temperature, χ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> ), for a cable-in-conduit-conductor (CICC) in the SULTAN test facility has been developed. The same kind of measurements are performed for the corresponding free standing filaments used for the cable manufacturing. The comparison of both the χ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> ) curves allows at first to measure the critical temperature ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tc</i> ) distribution in the CICC cross-section and then to infer from that the corresponding thermal strain distribution (ε <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</i> ). The ε <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</i> plays an important role in the monitoring of the performance degradation that a CICC experiences when it undergoes an electromagnetic cyclic load, allowing also to discriminate between reversible and irreversible degradation. A broadening of the strain distribution with the number of cycles is visible. The strain distribution was measured for both toroidal field samples and central solenoid samples. In both cases the ε <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</i> distributions have peaks at negative strain but the toroidal field sample distributions show a larger percentage of filaments in the tensile region.