Liquid nitrogen cooling for the Compact Ignition Tokamak

The Compact Ignition Tokamak (CIT), which is currently being designed, will have toroidal and poloidal magnetic-field coils precooled by liquid nitrogen to a temperature near 80 K prior to each plasma pulse in order to take advantage of the lower copper resistivity at reduced temperature. To maintain this temperature, the field coils, vacuum vessel, and surrounding structure will be enclosed within a cryostat. During a full-power D-T pulse, nuclear and resistive heating will impart a heat load of 11.0 GJ to the coils, raising the temperature of certain areas of the coils to near room temperature. The cryogenic system will supply 60000 kg (19500 gal) of liquid nitrogen to remove the heat with a 60-min cool-down period between pulses. The nitrogen requirements are discussed, and the cooling system is described. Other operating modes (standby operation and initial cool-down from room temperature) are also described. Results of a safety analysis indicating that the cryogenic system will meet all applicable environmental requirements are reported