Design of the 80 K helium circulation loops for ITER.

The thermal shields of the ITER machine must be cooled using helium circulating at 80 K. The ITER cryopumps also require intermittent helium cooling power at this temperature level. As a result two forcedflow helium cooling loops supplied by liquid nitrogen have been developed. Each 80 K loop comprises of an integrally geared centrifugal compressor able to compress up to 4 kg/s between 1.6 and 1.8 MPa and a perlite insulated cold box. This paper outlines the process requirements for the 80 K loops and the process design chosen in order to answer them. It justifies the technology chosen for the compressors and explains how the associated shaft seal leaks are being treated. Finally, it describes significant features of the cold boxes including the selection of a diffusion bonded stainless steel heat exchanger as well as associated key control loops.