Low coupling loss core-strengthened Bi:2212/Ag Rutherford cables
In a comprehensive "vertically integrated" program multifilamentary (MF) high temperature superconducting (HTSC) Bi:2212/Ag strand was fabricated using the powder-in-tube process and heat treated in oxygen by a modified standard procedure. The reaction-heat-treatment (HT) was adjusted to maximize critical current (density), I/sub c/ (J/sub c/), as measured in various magnetic fields, B. A series of Rutherford cables was designed, each of which included a metallic (Nichrome-80) core for strengthening and reduction of coupling loss. Prior to cable winding a series of tests examined the possibility of strand "poisoning" by the core during HT. Small model Rutherford cables were wound, and after HT were prepared for I/sub c/(B) measurement and calorimetric measurement of AC loss and hence interstrand contact resistance I/sub c/(B). It was deduced that, if in direct contact with the strand during HT, the core material can degrade the I/sub c/ of the cable; but steps can be taken to eliminate this problem. Otherwise the core is unequivocally beneficial: the cored Bi:2212/Ag cable is mechanically strong and easy to handle and, from AC-loss results, yields an ICR that when extrapolated to Large Hadron Collider (LHC) inner-winding specifications predicts a cable with a fairly satisfactory combination of low coupling loss and stability.