Simulation of Decay of Shielding Currents in ITER-TF Joint Samples

As a qualification test of ITER-TF coils, each joint sample was tested prior to manufacture of each TF coil. Eleven joint samples were tested by a conductor test facility with a 9 T split coil. The joint sample comprised two short TF conductors that had twin-box joint terminals at both ends. The lower joint is a testing part that is a full-size joint of the TF coil. Hall probes were attached on the lower joint box to measure the field induced by shielding currents. In order to simulate the shielding currents, an equivalent current circuit has been considered. The main loop of the shielding currents is the current flow in two conductors with crossing the jointed plane twice. The other two loops are the current loops inside superconducting cables in the two conductors. The resistance of the latter loops is given by twice the value of an average contact resistance between the superconducting strands. The calculated results are in good accordance with the experimental data, with an assumption that the overall joint resistance is decreased at low current. This phenomenon can be explained by the existence of a few strands contacting the joint box with extremely low joint resistances