Design and analysis of the superconducting current feeder system for the International Thermonuclear Experimental Reactor (ITER)

Abstract

The superconducting magnet system (SCMS) of the International Thermonuclear Experimental Reactor (ITER) consists of 18 D-shaped Toroidal field (TF) coils, 6 Poloidal field (PF) coils, one Central Solenoid (CS) coil and 18 Correction coils (CC). The TF coils will be operating with a conductor current of 68 kA; whereas the maximum current in the PF coils is 45 kA (back-up mode is 52 kA), in the CS coil 45 kA and in the Correction coils (CC) 10 kA respectively. In order to supply such high currents from the power supplies to the SCMS, a current feeder system is required. It mainly consists of the superconducting (sc) bus bars, the current leads, and the water-cooled aluminium bus bars. Each sc bus bar has a length of ∼25 meters. It consists of 1800 NbTi/Cu strands embedded in a stainless steel jacket (so-called cable in conduit conductors, CICC) and is cooled by forced flow supercritical helium. The sc bus bars specifications, the feeder conceptual design and the electromagnetic, thermohydraulic and quench performances are evaluated. The main consumers of cooling power in sc fusion magnet systems are the current leads. The current lead connects sc bus bar at low temperature side (4.5 K) to the water-cooled bus bar at the room temperature (RT) side. Because it is a solid connection between the RT and the 4.5 K level, the heat load to the low temperature region is associated with thermal conduction and Joule heating along the current lead system. An optimum, reliable and low loss current lead system is essential for large superconducting devices. Massive savings in capital investment as well as operation costs would be possible if replacing the actually planned conventional current leads by HTS current leads. In this context, a comparative study of the ITER design with conventional and with HTS current leads has been carried out. An obvious but also challenging option is the substitution of a part of the water cooled aluminum bus bars by HTS feeders. The design and optimization study of HTS feeders for ITER are based on Bi-2223/Ag superconductors and a conceptual layout are discussed. The cooling aspects and thermo hydraulic analysis of the HTS feeders has been carried out. The design parameters of the HTS feeder termination are summarized. Finally, a techno-economical comparison between the water-cooled aluminium bus bars and the HTS feeders has been carried out for ITER. It is shown that HTS materials have reached their maturity and efficient calculation tools are now available for better design and optimization of the superconductor current feeder system including current leads using HTS materials.