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.