Upgrade of CICC Mechanical Model and Case Study of ITER TF Conductor in Cold Test Conditions

This paper proposes to use an upgraded version of the Multifil simulation tool to model an ITER TF-like conductor in two cases: In tokamak and in cold test conditions. After briefly introducing the Multifil code, the paper will report the latest upgrades in terms of thermal equilibrium as well as simultaneous Lorentz and coil operational loads. We will present a new post-processing of the fractured filamentary area, which relies on a memory of the fracture map along all the loading steps. Then, considering ITER is currently building a magnet coil test bench (MCTB) with the capability to cold test some of the TF coils at nominal current (68 kA) in a standalone situation, we will discuss how mechanical modelling of the TF conductor is relevant for assessing the impact of the test sequence on the Nb₃Sn conductor degradation. We will present a new loading sequence, representative of the test facility conditions, with a different Lorentz force direction and amplitude with respect to tokamak operation. Furthermore, the MCTB test implies an additional over-compression of conductors located in the straight leg of the TF coil in equatorial plane. The effect of this “cold-test cycling” will be discussed in terms of mechanical behavior, fracture of strands and tentative Tcs degradation estimation.