Design methods and actual performances of conductors for the superconducting coils of tokamaks

Conductors presently retained for the coils of large fusion machines are cable-in-conduit conductors made of about one thousand of superconducting strands cabled inside a jacket and cooled by a forced flow of helium. The current density is the key parameter for die machine design, as it reacts strongly on the size and on the cost. An optimized conductor design has been pursued to maximize the current density while fulfilling several criteria regarding protection, stability and safety margin. The influence of some parameters such as: field, strain, effective diameter of filaments and heat transfer coefficient is analyzed. A Nb₃Sn conductor developed by CEA relevant for NET/ITER has been tested successfully at 6.2 K up to 50 kA and 12 T. Following the same concept a complete design of a conductor for the central solenoid of ITER is proposed