Bi:2212/Ag-based Rutherford cables:: production, processing and properties

The fabrication of Bi:2212/Ag-based Rutherford-type accelerator cables, their transport critical current (I-c) testing and ac loss measurement are described. Multifilamentary strands were used to form several cables with 18-19 strands and a lay pitch, L-p (half the transposition pitch) of 27.5 mm. The inclusion of a metallic alloy core was proposed for mechanical strength, the limiting of cable winding damage and ac loss/residual magnetization mitigation. Single-strand measurements of 'poisoning' from several candidate core materials are reported, as well as the influences of winding pitch and thermal shock degradation on I-c. Nichrome 80 was selected as a core material on the basis of ready availability in strip form and its initially observed inertness from a poisoning standpoint. In-cable single-strand studies indicated that winding damage could degrade edge-measured I-c by about 16%. Full cable I-c measurements demonstrated that core-induced poisoning could reduce I-c by a further 35-40%. Ac loss measurements on a series of specially designed cables showed that the core (either bare or coated) effectively insulated the strands against crossover contact. This, together with the fact that the cable had been only lightly compacted (thereby ensuring moderate but not strong side-by-side contact) allowed the effective interstrand contact resistance of a projected Bi:2212/Ag-wound core-type LHC Rutherford cable to fall close to the acceptability range for the windings of accelerator magnets.