1926 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011 Simulation of Interstrand Coupling Loss in Cable-In-Conduit Conductors With JackPot-AC E. P. A. van Lanen and A. Nijhuis Abstract—Within the framework of the design analysis of ITER PF coil joints, a model is developed that simulates the coupling loss between strands in a cable-in-conduit conductor (CICC). The present version of this model can simulate these losses in a cable section, subjected to any type of time-changing background field. It calculates the trajectories of all strands in the CICC, and uses this as the foundation for the electrical properties of the model, including strand transport properties, saturation and shielding. The simulation results are first compared with measurements on sub-size CICCs with different strand coating, which affects the in- terstrand resistance. In all but one of these simulations, the cou- pling loss time constants are lower than the measured values. A better agreement is obtained with the simulation of an ITER PF1 conductor, subjected to Twente Press experiments. For this simula- tion, only one final stage sub-cable is used, assuming that coupling currents between them is negligible due to the stainless steel wraps around them. Index Terms—CICC, coupling loss model, ITER, supercon- ducting strands. I. INTRODUCTION T HE ITER tokamak contains six Poloidal Field (PF) coils to provide shaping and vertical stability of the plasma. They are designed with NbTi Cable-In-Conduit Conductors (CICCs), which are wound in double-pancakes, and connected in series with joints at the outer diameter [1]. Although stability analysis of these coils concluded that they will operate success- fully within the specified temperature margin [2], [3], a more detailed analysis on the coil joints was also recommended [4]. There are essentially two reasons for this: First, the transport current is not fully transposed in the cable inside the joint, and close to it, making this region more vulnerable for instability [5], [6]. The second reason concerns the orientation of the back- ground field with respect to the joints. The joints are placed in a position where they are expected to suffer the least from the longitudinal component of the PF coil’s field. However, the loss due to other components of the background field, not only from the same PF coil, but also from other coils in the system, has not yet been investigated. Estimating the effect from the current non-uniformity and the field orientation on the thermal stability of the joints requires a highly detailed model. Such a model was already developed Manuscript received August 03, 2010; accepted September 25, 2010. Date of publication November 09, 2010; date of current version May 27, 2011. This work was supported by ITER under Service Contract No. UT-ITER/CT/09/ 4300000070. The authors are with the Faculty of Science and Technology, Univer- sity of Twente, 7500 AE Enschede, the Netherlands (e-mail: e.p.a.van- lanen@tnw.utwente.nl). Digital Object Identifier 10.1109/TASC.2010.2082474 Fig. 1. Illustration of the CICC division in Cable Sections (CS), separated by Cable Intersections (CIS). earlier to analyze the DC behavior of CICCs [7]. This model (JackPot) accurately calculates the trajectories of all strands, and deduces all electrical properties from this. It is fully based on ex- perimentally determinable conductor properties, such as strand parametric scaling laws and interstrand contact resistances. It has been used successfully to explain the differences between short and long length samples of ITER PF conductors [8], and is now being expanded with time-dependent components. This paper describes the first step, in which only a short length of CICC is considered, which is not connected to a power source, and placed in a homogeneous background field that changes in time. This makes it already possible to simulate coupling loss measurements on cable sections in a solenoid or dipole magnet, and to perform parametric studies. II. MODEL DESCRIPTION Similar to other models [6], [9], [10], JackPot-AC simulates the CICC as a network of (mutual) inductances, induction voltage sources and two types of resistors; one that represents the electrical contacts between strands, and one that involves the superconducting strand properties (see Fig. 1). The back- bone of the model is the cabling subroutine. It calculates the coordinates of the central axes of the strands, which are used to determine many of the electrical properties [7]. For example, an interstrand conductance is only present between strands if they are close enough together. The strand trajectories are now also used to calculate the mu- tual inductances. For this, it is assumed that the coupling takes place between all piecewise linear sections that represent the strands, including the sections that belong to the same strand. The calculation of a section’s self inductance is done with the theory described in [11]. The total self-inductance of a single 1051-8223/$26.00 © 2010 IEEE