A New Cabled Stabilizer for the Nb3Sn React&Wind DEMO Conductor Prototype

Abstract

A Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn based, React&Wind flat cable, named RW2, was developed in the past three years at the Swiss Plasma Center in the scope of the EUROfusion conceptual studies for DEMO. The test results presented earlier proved an excellent DC performance, but large eddy currents loss in the segregated copper. Here we present the results of a prototype conductor assembled in late 2019 from an older section of RW2 cable and a novel stabilizer, made by two Rutherford cables of thick, high RRR copper wires extruded with a cladding of high resistivity CuNi alloy. The results of the test in SULTAN of the new prototype are discussed in terms of DC and AC loss performance. The AC loss is measured in both orientations, for sinusoidal and trapezoidal field pulses. The test is carried out at both 4.5 K and 20 K operating temperature, allowing separating the contribution of the eddy currents in the segregated copper from the other sources of ac loss, hysteresis and coupling loss. The goal of reducing the eddy currents to a level comparable to the coupling current loss is achieved with the cabled stabilizer, which is now retained as baseline for the React&Wind DEMO conductor.