Stabilization and cooling requirements for the alcator DCT superconducting magnet system

Alcator DCT, an experimental tokamak to be constructed at M.I.T., will be the first tokamak in the world with entirely superconducting magnets. The combined objectives of the toroidal field (TF) and poloidal field (PF) magnets are ambitious and prototypical of reactor-scale magnets, such as those considered for the Toroidal Fusion Core Experiment (TFCX). The superconducting magnets must carry currents up to 23 kA, with maximum terminal voltages of 20 kV, and should not be driven normal by disruptions, following an initiation blip and plasma start-up. The cryogenic load is dominated by current lead losses and pulsed field losses, and also includes joint, thermal radiation and cold mass support losses. The refrigerator load topology includes a naturally circulating twophase pool of helium for the TF coils and either that or forced-flow, single phase helium for the PF coil winding packs. Single phase helium is provided to the PF coil cold cases and liquid nitrogen to the outer vacuum dewar