Mechanically Reinforced Bi-2212 Strand
Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current density is large under high fields, particularly with recent enhanced results. The Bi-2212 conductor may be a round strand: a very favorable shape to wind and to make high-current Rutherford cables required for protection. There is no satisfying high-current cable with YBCO. One drawback of Bi-2212 is their low mechanical properties. Large fields and current densities indeed induce high mechanical stresses. To improve the mechanical properties of Bi-2212 strands, Nexans has proposed to reinforce it with a metal sheath wrapped around using their process of shaping and welding. The sheath is wrapped around the strand and laser welded, and the whole is drawn to a diameter of 0.9 mm. Several materials for the sheath were studied to determine their resistance to thermal treatment of Bi-2212 and their mechanical properties after treatment. We choose Inconel 601. A method of perforating the sheath has been developed to enable the oxygenation during the heat treatment. A 6 + 1 conductor has also been produced around an Inconel core and inserted in a tube. The 6 + 1 reinforced conductor was then drawn to a diameter of 2.7 mm. The Ic measurements at 4 K show that our mechanical reinforcement does not significantly lower the transport capacities. They therefore validate the method and the heat treatment.