DC resistance and eddy current losses in the ITER conductor joint

The central solenoid (CS) and the toroidal field (TF) coils of the International Thermonuclear Experimental Reactor (ITER) are wound from superconducting (SC) Nb/sub 3/Sn Cable-in-Conduit-Conductor (CICC). Electrical joints are an important aspect of the coil design, since local heating from resistive losses can drive the superconductor into a less stable regime and possibly initiate a quench. A good joint design will satisfy the broadest requirement which is to minimize the power dissipation during normal coil operations. This can be achieved by satisfying two, more specific, and in some ways, conflicting requirements: (1) to provide a low DC resistance, and (2) to minimize the effects of Joule heating from eddy currents induced by transient magnetic fields. This paper presents a finite element analysis of the latest conductor joint concept and evaluates its electromagnetic characteristics with respect to these two requirements. The analysis extends the usual practice of representing the presence of superconductors with surface conditions by explicitly modeling the last stage of the twisted cable. Although certain modeling approximations limit the accuracy of the results, some valuable insights are gained, such as which approximations cannot be made, and the effects of various design details on the DC joint resistance and Joule heating.<>