Investigation of divertor movement during disruptions in ASDEX Upgrade

The divertor serves as the main power exhaust of tokamaks. Hence the target tiles in the divertor must be carefully aligned to prevent leading edges which would result in higher power deposition and subsequent melting. The outer strike line in the lower divertor of ASDEX Upgrade is located on the assembly 1, which consists of the target tiles, the cooling plates and the support structure. Since the transition to the tungsten optimized divertor design of the divertor in 2014, it has been observed that the assembly 1 and the underlying frame are displaced over the course of an experimental campaign. The attachment of the assembly has been modified several times to prevent this displacement. However, a complete suppression of the movement was not achieved. The reason for the displacement is suspected to be due to induced currents and the resulting jxB forces during disruptions. This was investigated using a full 3D transient model of the ASDEX Upgrade coil system and a model of the assembly 1 with frame and vacuum vessel. The different assembly modifications and several current quench times were simulated, resulting in forces of up to 5.5 kN and torques up to 6.3 kN m. These forces were then used in a 3D transient structural model of the assembly to investigate the resulting displacements. It was found that displacements occur in all cases but they vary between 0.25 mm and 0.75 mm.