Dynamic response of the ITER diagnostic upper port plug during a plasma disruption

The diagnostic upper port plug in ITER is a long metal box cantilevered to the vacuum vessel port with 42 × M52 studs and nuts. The plug structure has a heavy payload at the front such as the Diagnostic First Wall (DFW) and the Diagnostic Shield Module (DSM) to protect the diagnostic components from plasma and neutron fluxes. This kind of structural configuration is susceptible to a resonance with the transient external load. For the upper port plug, the design-driving load is electromagnetic (EM) forces due to plasma disruptions. In this study the dynamic amplification factor (DAF) of the structure is calculated for such EM loads. The bolted joint at the back flange of the plug structure is also taken into account together with the port extension of the vacuum vessel and its influence on the dynamic behavior is investigated. The analysis results show that the bolted joint reduces the DAF as well as the natural frequency of the structure.