The Requirements for the Fast Interlock System of Wendelstein 7-X

The purpose of the Wendelstein 7-X central safety system (css) is to minimize the risk of injury to personnel and damage to equipment. The design of the css follows the IEC 61511 standard for functional safety in the industry. Due to the nature of the hardware used, the reliability of the system is high and the response time is moderate (in the order of seconds). To protect the components inside the plasma vessel during plasma operation, the response time must be much faster (on the order of 100 ms). As part of the safety control system, the fast interlock system (FIS) has been installed but with different hardware to that used for the css. The purpose of this article is to present the design process, starting with a risk assessment for the components inside the plasma vessel due to thermal loads, which determines the requirements for the FIS. The basic design criteria for the FIS to ensure the principles of functional safety are described.