Analysis of Quench Propagation in the ITER Central Solenoid Insert (CSI) Coil

The Central Solenoid Insert (CSI) coil, a single-layer Nb3Sn solenoid, wound using the same conductor of the 3L module of the ITER Central Solenoid, was tested in 2015 at the National Institutes for Quantum and Radiological Science and Technology (former JAEA) Naka, Japan, inside the bore of the Central Solenoid Model Coil. At the end of the test campaign, quench tests were carried out to study the quench initiation and propagation. Different delay times (up to 7 s) between quench detection and current dump were set, in order to explore to which extent the dump could be delayed without exceeding the maximum allowed hot spot temperature. The experimental data for different time delays are presented and compared, showing a good reproducibility of the measurements and confirming the safe operation of the coil during these tests. The previously developed and already extensively validated 4C thermal-hydraulic code is then used to model the transient up to the current dump and a comprehensive comparison between the simulation results and the measurements is presented, including the evolution of the local voltages and of the jacket temperature distribution along the conductor, the quench front propagation, and the SHe pressurization and mass flow rate behaviour measured at the CSI inlet and outlet. The good agreement between simulation results and measurements confirms the validation of the 4C code for this type of transients and the code is then used to explain the acceleration of the quench and to get an improved estimate of the hot spot temperature.