Study of the Hot-Spot Temperature During Quench in the Nonplanar Coils of W7-X

The quench protection system of the nonplanar coils of the Wendelstein 7-X stellarator was laid out over 15 years ago. At that time, the assessment of the hot-spot temperature by a basic adiabatic model was done using design values for material and operation parameters. After the operating experience in 2016, the hot-spot temperature is reassessed with the thermal-hydraulic program THEA, using the actual values for delay and dump time. The electrical resistivity of the conduit alloy ismeasured over the whole range of temperatures and in magnetic fields on relevant samples of a conductor, exposed to the hardening heat treatment after winding. The results were fed into THEA. Parametric variations are studied in the calculations, e.g., testing the effect of the quench initiation zone, delay time, and dump resistor. The results suggest that the hot-spot temperature of the conduit in the case of quench is safely within the allowable values even when the dump voltage is reduced compared to the initial design value.