JackPot: A novel model to study the influence of current non-uniformity and cabling patterns in cable-in-conduit conductors

JackPot is a new model that is used to analyse how and to what extend current non-uniformity among strands in a cable-in-conduit conductor (CICC) affects its performance. The joints at the extremities of the CICCs in coils and short samples introduce a non-uniform current distribution among the strands. A detailed and quantitative study down to strand level is required to explain the involved phenomena, to understand their implications on short sample and coil tests and to provide adequate solutions for improvements. The model can be used to evaluate the influence of the joint design and to define its baseline requirements for short-sample qualification testing, and for optimum magnet performance of for example the ITER coils. JackPot is an electrical network model that simulates the interaction between the superconducting strands in the cable (following their precise trajectories), the interstrand contact resistances, the conduit, and the cable’s connection to the joints. The backbone of JackPot is its cable geometry model, from which all relevant properties are derived. All parameters are derived from well defined experimental measurements on conductor sections and joints, except the axial strain for Nb3Sn strands, which is the only free parameter in the model. The simulations demonstrate that the current non-uniformity is the source for a number of observed phenomena. Another conclusion is that completely filling the bottom joints and upper terminations of a short sample with solder, opposed to only (partly) soldering the cable surface, improves short-sample testing significantly for qualifying the ITER type CICCs. This paper describes the model and gives a few examples of applications for its validation.