Abstract-The Wendelstein 7-X (W7-X) modular stellarator is in the assembly phase at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The design of the "basic machine", i.e. without in-vessel components, diagnostics and periphery, is largely completed, structural parameters such as bolt preload, initial conditions for contact elements, etc. are defined, and most of the components are manufactured and partly assembled. Therefore, the focus of structural analysis was shifted towards fast analyses of nonconformities, changes in the assembly procedure, and exploration of operational limits. Assembly-related work is expected to continue until commissioning of the machine, however, with decreasing intensity. In parallel the analysis requirements for in-vessel components, diagnostics and periphery will increase. This paper focuses on the most remarkable results, on special problems which had to be solved, on strategic issues like parameterization, complex finite element model structuring and benchmarking with alternative models in different codes, on assumptions of reasonable safety margins and expected tolerances, and on confirmation of analysis results by tests. Finally it highlights some lessons learned so far, which might be relevant also for other large fusion machines, and gives an outlook on future work.

The Wendelstein 7-X (W7-X) modular stellarator is under construction at the Max-PlanckInstitut für Plasmaphysik in Greifswald, Germany. The W7 X magnet system contains 70 superconducting (sc) coils which are supported by a massive central steel ring structure via bolted connections and by numerous welded as well as gliding inter-coil elements. Load tests on prototypes of bolted coil to support ring connections whose flanges partially open during high field operation, and of sliding support structures between the coils showed that stick-slip events at their contact surfaces cause shock waves. In order to assess the risk of a shock-induced quench of the superconductor, one of the coils was subjected to impact loads -the so called mechanical quench (MQ) test -in the course of the cryogenic acceptance tests at CEA in Saclay, France. No quench could be triggered even with the lowest coil stability margin. The paper demonstrates that the amplitudes of the shock waves in the W7-X magnet system are comparable to those generated by the impacts in the MQ tests. For that purpose, finite element (FE) models of both W7-X and the MQ test simulating the dynamic responses were developed and successfully validated against measurements. The Wendelstein 7-X (W7-X) modular stellarator is under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The W7-X magnet system contains 70 superconducting (sc) coils which are supported by a massive central steel ring structure via bolted connections and by numerous welded as well as gliding inter-coil elements.Load tests on prototypes of bolted coil to support ring connections whose flanges partially open during high field operation, and of sliding support structures between the coils showed that stick-slip events at their contact surfaces cause shock waves. In order to assess the risk of a shock-induced quench of the superconductor, one of the coils was subjected to impact loads -the so called mechanical quench (MQ) test -in the course of the cryogenic acceptance tests at CEA in Saclay, France. No quench could be triggered even with the lowest coil stability margin.The paper demonstrates that the amplitudes of the shock waves in the W7-X magnet system are comparable to those generated by the impacts in the MQ tests. For that purpose, finite element (FE) models of both W7-X and the MQ test simulating the dynamic responses were developed and successfully validated against measurements.

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