Conceptual Design of a Hollow Cable Conductor for the Large Coil Program

摘要

Westinghouse selected forced flow, supercritical helium-cooled Nb sub 3 Sn hollow cable conductors forthe Large Coil Program (LCP). A number of requirements and constraints were specified for the design of the model coil. Those that have direct and indirect impacts on the conductor design were: the conductor must recover spontaneously to the superconducting state when half a turn is driven normal initially; total refrigeration load must be less than 550 W when the coil is operating with the full current; total refrigeration load must be less than 100 W when the coil is operating at 80 percent of the full current; the peak magnetic field is to be 8 teslas; and the maximum conductor current is 16,000 A. The conceptual TF coil is a pancake-wound device where each pancake of aluminum contains a number of conductor slots. Each slot accommodates 5 parallel turns. The basic conductor concept selected consists of cabled triplexes, initially enclosed in a round pipe stainless steel jacket and then compacted to a square configuration with the desired void fraction. Examination of a typical conductor cross section suggested a number of uncertainties that affect the conductor design, e.g., the uniformity of helium flow in the interstices of the twisted strands, the uniformity of current flow among the strands during conductor recovery, the load-bearing capability of the conductor, the heat transfer coefficients, and the friction factors for twisted-strands compacted hollow cable conductors. These uncertainties and the lack of prior experience in the design of superconducting devices with hollow cabled conductors suggested that conservative assumptions be used. The design approach and the selection of a reference design are discussed. (ERA citation 04:011202)