Conceptual design of a hollow cable conductor for the large coil program

A conceptual design of a cryostabilized conductor was developed for the Large Coil Program (LCP) that met all of the stringent design requirements and constraints. The reference conductor was selected following parametric analyses involving the number of strands, the helium (void) fraction and the copper to noncopper ratio. The number of strands considered took into account the type of cabling operations that are possible and the need to provide complete transposition of the strands to minimize ac losses. The helium (void) fraction affects the pressure drop and helium pump work required, while the copper to non-copper ratio affects the helium flowrate required to meet the stability criterion. The reference conductor selected consisted of 567 strands of multi-filamentary superconductors with a copper to non-copper ratio of 1.92. The stability of the reference conductor selected was verified by transient recovery analyses using the TAP-B code. There are a number of uncertainties that affect the stability of the conductor. They include the heat transfer and helium flow phenomena within the interstices of the twisted strands. These uncertainties as well as the heat transfer and friction factor correlations used in the design and the various assumptions made are discussed in the paper. Areas where additional work are needed are recommended.