Voltage-temperature characteristics in model coils using a Nb3Sn cable-in-conduit conductor for ITER

Two types of model coils (MC) were recently tested in order to assess possible designs of the international thermonuclear experimental reactor (ITER) conductor and Joints for the Toroidal field (TF) coils. One of these MC is wound using a stainless-steel-jacketed conductor, the Toroidal field model coil (TFMC), and the other a Ti-jacketed conductor, the Toroidal field coil insert (TFCI). This paper is dedicated to the electrical behaviour of these conductors through the V-T characteristics. In a first part we present the analysis of experimental results with a global thermo-electromagnetic model in which the current distribution is supposed uniform among the strands. Emphasis is put on all elements making the operating conditions of strands in a coil different from those of a single strand test (global strain, magnetic field and temperature gradients). The second part is dedicated to current distribution non-uniformity effects, either considered at the strand scale (TFMC) or at the subcable scale (TFCI). For this purpose, CEA developed a code (ENSIC) based on an electrical model network simulating conductor lengths and the associated joints. This model is applied to both coil tests. The last part includes a discussion on the validity and precision of the results provided by both models, compared to the experimental measurements. (C) 2003 Elsevier B.V. All rights reserved.