Alcator DCT conceptual design

A 2 meter major radius superconducting tokamak is now under design to serve as a follow-on to the high field Alcator tokamaks at MIT. The machine will be RF heated with 5 MW of CW ICRH, and will be capable of either essentially continuous operation using 4 MW of CW LH current drive, or pulse times of 100 seconds using ohmic drive. The 1 MA plasmas can be elongated up to γ = 1.4 and will be optionally diverted utilizing a poloidal divertor. The average CW wall and collector heat fluxes will be in the reactor range namely 0.20 MW/m2 average wall loading, and 2 MW/m2 average collector loading. The 550 MJ toroidal field system consists of 24 Dee shaped (1.25 X 1.55 m) Nb3Sn coils with a peak field of 10 T, constructed of internally-cooled conductor similar to that used in the Westinghouse LCP coil. The coils are supported by heavy-wall structural cases, which also contain atmospheric pressure liquid helium. This secondary cooling serves to remove the average heat load from the potted double pancakes, eliminating the need to circulate the internal supercritical helium which provides only a transient stabilization function. The ohmic heating poloidal field coils are also superconducting. The current conductor design is based on an internally cooled NbTi conductor, with a tube-within-a-tube cooling concept. The ohmic heating coils store 120 MJ and provide 35 volt-seconds, with a peak field of 7 T, and an average field change of 3 T/s during the 1.5 s current ramp