A Study on Quench Detection for Cable-in-Conduit Conductors With Co-Wound Tapes

The primary Quench Detection System (QDS) of the Central Solenoid (CS) of the ITER magnet system must be able to distinguish the resistive component of the voltage, arising during quench, from the inductive one due to time-varying magnetic fluxes. This task is especially challenging for the six modules composing the CS (CSMs), with a coil self-inductance of the order of ∼1 H, subjected to current ramps up to ∼10 kA/s. Each CSM is equipped with stainless-steel tapes wrapped around the outer conduit of the conductor, referred to as Co-Wound Tapes (CWTs), linked to a magnetic flux approximating the one linked to the conductor itself. This work focuses on the definition of a model able to compute the voltages measured by the QDS with the high precision required. The analysis is based on a 2D axisymmetric FEM model of the entire CSM in a stand-alone configuration. A novel 3D approach based on an integral computation method allows one to account for the twisting of the conductor sub-cables of the last cabling stage (petals). The model is applied to quantify the impact of three main error sources contributing to the residual voltage signal measured by the QDS: the difference in self-field flux linked to the conductor and to the CWT, the inhomogeneity of the background field and the twisting of the petals.