Realization of the requirements for a safe operation of Wendelstein 7-X

The Wendelstein 7-X superconducting stellarator is a fusion experiment designed for processing of plasma discharges in the range of some seconds up to 30 min in a quasi-steady state operation mode. The first plasma experiment was conducted in December 2015. Since this first plasma experiment, more than 100 experimental days with about 3500 plasma experiments were successfully performed within three operational phases. The operation of W7-X requires the handling of many different sources of hazards with different hazardous potentials for persons and for the device. To identify critical hazards, risk analyses and risk assessments are carried out at an early stage in the development process for all W7-X technical components and diagnostics, so that measures for risk mitigation can be taken into account already in the design. The main objective of this process is to ensure safe operation for the personnel and to protect the investment in the W7-X device. In this work, we present the safety model for W7-X operation. After a brief introduction to the architecture of the W7-X control system, the process of regarding the safety requirements will be discussed. In addition, the multi-shell safety model for the technical implementation of risk mitigation functions at the various levels of the W7-X control system is described. The experiences at W7-X during the previous operating phases obtained with the implemented safety concept will be described. Finally, a preview of the enhancements and modifications of the safety systems for the next operation phase OP2, which will start in 2021, is given.