Simulations of Twin-Box Joints for ITER PF Coils

An ITER Poloidal Field coil winding consists of stacked double pancakes wound with NbTi cable-in-conduit conductors. One of the critical components of the coil is the electrical joint connecting either two conductor lengths within a double pancake or two double pancakes. All joints utilize the twin-box “shaking hands” concept. It has previously been found with the JackPot-AC numerical model that in these joints the sum of the transport and induced currents in some of the superconducting strands during coil operation may exceed the strands' critical current. It was decided to further explore the behavior of the joint with a simplified set of current and magnetic field runs. A solution for the reduction of the induced currents is proposed and verified by modeling. The paper discusses the results of the simulations and gives recommendations for the joint design.