Effect of Temperature and Deformation on Nb3Sn Strands Instabilities

Abstract

The critical current of Nb3Sn strands used in Fermilab’s high field magnets was measured at low and high fields under various experimental conditions using the voltage‐current (V‐I) and voltage‐field (V‐H) methods. The strands were commercially produced using Restack Rod Process (RRP) and Powder‐in‐Tube (PIT) technologies. Both round and deformed strands were studied. Measurements were performed at the Fermilab’s Short Sample Test Facility using a 2‐kA sample holder with a low contact resistivity. V‐I characteristics at fields above 10–12T with a smooth transition from the superconducting to normal phase allowed determining strand critical current. V‐I and V‐H measurements at low fields showed premature quenches due to magnetic instability in strands with high critical current density and large effective filament size. The effects of strand deformation and RRR as well as test temperature were studied. This paper describes the Nb3Sn strand parameters, the equipment and measurement methods used, and the res...