DC Characterization of a Low-Field Nb3Sn Prototype Conductor for a DEMO TF Coil

A Low Field W&R (Wind and React) conductor, developed in the frame of the conceptual design studies for the Toroidal Field (TF) coils of DEMO, has been designed to be constituted of a small number of superconducting Nb3Sn strands and a high number of stabilization copper wires. It has been extensively characterized at the SULTAN facility at Swiss Plasma Center (SPC) in February 2021. The conductor has been operated up to its target current, 70.8 kA, and characterized up to a background magnetic field of 10.78 T. The test program included AC loss measurements, current sharing temperature (T-cs) and critical current (I-c) measurements before and after cyclic loading. Critical temperature (T-c) measurements were performed on the virgin conductor at the beginning and at the end of the test campaign. In this work we are focusing on the DC characterization, while the AC measurements analysis will be the object of a following work. Concerning DC tests, premature quench phenomena prevented from operating the conductor at the target current - field conditions. Nevertheless, at lower currents T-cs stability was observed, with no performance degradation due to cycling. The present paper investigates these results and tries to give an explanation through measurements and tomographic analysis. Furthermore, the achieved strain distribution in the conductor, obtained by means of inductive measurements analysis, will be shown. The implications of the design approach on the performance, based on the outcome of such tests, are discussed.