Enhancements of the Fast Interlock System for Wendelstein 7-X Operational Phase OP 2.1

An extended modification phase of the superconducting fusion experiment Wendelstein 7-X (W7-X) was completed late 2021 after installing actively cooled divertor units and the integration or modification of new technical components and diagnostics. Currently, the commissioning of the W7-X experiment is underway. First, technical plasma operation is scheduled for the end of September 2022, and scientific plasma operation will start at the end of November. The fast interlock system (FIS) is an important component of the safety instrumented system (SIS) of W7-X. The main task of the FIS is to protect the inner plasma vessel components from thermal overload from both plasma heating systems (e.g., neutral beam injection) and the plasma itself. There are strict limits for reaction times after detection of interlock relevant events, which have to be observed in order to prevent overload situations of the first wall. The requirements for the FIS were substantially modified and extended, in order to address the challenges due to the actively cooled divertor. This led to extensive revision of the technical implementation and the software of the FIS. In this article, after a short introduction of FIS design and operation in operating phase (OP1), the modification of FIS for OP 2.1 operation is presented. Finally, the first results during the OP 2.1 commissioning and operation of the FIS are discussed.