Mechanical Monitoring Issues in Preparation to Next Step of Wendelstein 7-X Operation

The largest modular stellarator Wendelstein 7-X (W7-X) has successfully passed the first phase of operation in Greifswald, Germany. The sophisticated W7-X superconducting magnet system (MS) with its nonlinear support system has been carefully monitored using an extensive set of mechanical and temperature sensors. This paper focuses on detailed consideration of cyclic MS behavior during operation with limiter configurations of plasma. Measurement results are carefully compared with predictions from updated numerical models and critical issues are highlighted. As a result, the structural monitoring tool is extended to follow enhanced requirements and expectations. This paper is a preparation for upcoming more demanding phases with longer plasma pulses to guarantee safe and reliable W7-X operation with different divertor and scraper element configurations. The procedure to establish required sensor configurations, and to analyze and release new plasma regimes being compatible with W7-X component design values is also described.