Current distribution and strain influence on the electromagnetic performance of the CS Insert

The Central Solenoid Model Coil (CSMC) is a solenoid consisting of 18 concentric layers, wound with Nb₃Sn cable-in-conduit conductor, jacketed with Incoloy. The Japanese HT and USHT were in charge of the manufacturing, and the coil is being tested at JAERI, Naka (Japan). The European Home Team is involved in the testing program, which includes electromagnetic characteristics of the CSMC, and of the CS Insert. Two effects influence strongly the electromagnetic properties: (i) connections introduce a nonuniform current distribution among the strands, and (ii) the performance of the strands are dependent on the strain of the Nb₃Sn filaments. The current distribution calculated in the CS Insert takes into account magnetic field and strain applied on the conductor, the joint effect and the current transfer between strands. The model developed at CEA, uses an equivalent electric network composed of resistive joints, superconducting lengths and interstrand resistances and provides the voltage-current characteristics, which ran be directly compared to the experimental results