Design and R&D for the central solenoid for the Compact Ignition Tokamak (CIT)

The CIT will require a liquid-nitrogen-cooled, pulsed poloidal field coil system for plasma heating, shaping, and control. The central solenoid will have a bore diameter of 0.8 m, a height of 4.8 m, and a central field of 23-256 T. Geometric restrictions are such that an aggressive structure concept is required. Two options are being considered for the machine. The first would require a self-supporting central solenoid consisting of a stack of explosively bonded copper/Alloy-718 plates with a copper/Alloy-718 ratio of 50/50. Each plate is cut into eight turns by a water-jet cutting process. Features of this design are presented along with selected results from an R&D program under way. Full-scale plates have been fabricated and cut, and prototypical mechanical and electrical joints have been tested. The other machine design option would allow the central solenoid to receive partial support from the TF (toroidal field) coil system. In this case the operating scenario and stresses are substantially different. R&D tasks have been started to evaluate conductor lifetime under simulated operating conditions for alumina dispersion strengthened (ADS) copper. Explosively bonded copper/Alloy-718 plates remain an option, but with a substantial increase in the ratio of copper to Alloy 718 to 70/30. The status of test results and plans for these materials is given