Recommendations for a cryogenic system for ITER (International Thermonuclear Experimental Reactor)

The International Thermonuclear Experimental Reactor (ITER) is a new tokamak design project with joint participation from Japan, the European Community, the Soviet Union, and the United States. ITER will be a large machine requiring up to 100 kW of refrigeration at 4.5 K to cool its superconducting magnets. Unlike earlier fusion experiments, the ITER cryogenic system must handle pulse loads constituting a large percentage of the total load. These come from neutron heating during a fusion burn and from ac losses during ramping of current in the PF (poloidal field) coils. This paper presents a conceptual design for a cryogenic system that meets ITER requirements. It describes a system with the following features: (a) only time-proven components are used; (b) the system obtains a high efficiency without use of cold pumps or other developmental components; (c) high reliability is achieved by paralleling compressors and expanders and by using adequate isolation valving; (d) the problem of load fluctuations is solved by a simple load leveling device; (e) the cryogenic system can be housed in a separate building located at a considerable distance from the ITER core, if desired. The paper also summarizes physical plant size, cost estimates, and means of handling vented helium during a magnet quench. 4 refs., 4 figs., 3 tabs