The manufacture of corrugated copper tubes with a Nb3Sn layer

Based on prior experience gained with superconducting materials, further research work was jointly carried out by our organizations. The purpose of this effort was the establishment of a production process for the manufacture of corrugated, high-purity copper tubes incorporating the thickest possible layers of superconducting Nb3Sn. The goal of the production process was to develop a corrugated, bendable superconductor as the core of a cryogenic envelope capable of withstanding reeling and unreeling on reels with barrel diameters up to 3 m, without damaging the brittle Nb3Sn layer. The manufacturing process is described in detail. The latest results show a superconductor with a critical temperature of 15.5 K, having a 10 micrometer layer of pure Nb3Sn, While not completely homogeneous, the sample is capable of carrying currents up to 125 - 140 A on a 10 mm sample width and in a magnetic field of 5 T. The corrugated tube acts at the same time as a self-compensating helium circuit and as the copper-stabilized current-carrying superconductor of a three-phase cable in a flexible cryogenic envelope. The envelope consists of four concentric corrugated tubes with an intermediate nitrogen shield. The resulting losses into the helium circuit are less than 0.2 Wm^-1. The experiments have been conducted, until now, on tube lengths up to 40 m. All steps were carried out on conventional, commercially available equipment.