${\rm Nb}_{3}{\rm Sn}$ Strand Characterization for the Nijmegen 45 T Hybrid Magnet

Abstract

The Nijmegen 45 T hybrid magnet will consist of an inner resistive 33 T resistive magnet and a superconducting 12 T outsert magnet. In the present conceptual design of the layer-wound outsert, the conductor is a Nb3Sn-Cu Cable-In-Conduit Conductor (CICC) with a stainless steel conduit, operating at 4.5 K by a forced flow of supercritical helium. At nominal magnetic field, the operating current is 12.3 kA. The outsert magnet design comprises 3 types of CICC design assuming a void fraction of 29 % and a temperature margin above 1.5 K. The design requires for 0.81 mm diameter Nb3 Sn strands a minimum copper fraction of 50% and a minimum equivalent critical current at 12 T, 4.2 K, ? = 0% of 590 A. A candidate strand considered is a Powder-In-Tube type of NbaSn conductor with 114 filaments and a copper fraction of 55 %. To predict the cable performance in terms of critical current, stability and AC loss under operational conditions to the best of present scaling capabilities, knowledge of the behavior of the critical current Ic(B, T, ?axial), magnetization M(B, dB/dt), stress-strain relation at 300 and 4.5 K and finally Ic as a function of periodic bending and temperature is required. These essential properties, as measured at the University of Twente employing the TiAIV Ic barrel, the PacMan and Tarsis strain devices as well as the integrating magnetometer, are presented and discussed.