The ITER interlock system

ITER involves the integration of numerous sophisticated systems, many of which must operate reliably close to their performance limits in order to achieve the project's scientific goals. The teams responsible for exploiting the tokamak will require sufficient operational flexibility to explore a wide range of plasma scenarios within an operational framework that ensures that the integrity of the machine and safety of the environment and personnel are not compromised. The instrumentation and control (I&C) systems of ITER are divided into three separate tiers: the conventional I&C, the safety system and the interlock system. This paper focuses on the last of these. The operational experience from existing tokamaks and large superconducting machines, together with many specific aspects of the ITER facility, have been taken into account in the design of the ITER interlock system. This consists of a central element, the Central Interlock System, and several local elements, distributed across the various plant systems of the tokamak and referred to as Plant Interlock Systems. Each Plant Interlock System is connected to dedicated networks and communicates its status and interlock events to the Central Interlock System, which in turn sends the required interlock actions to the Plant Interlock Systems. The Central Interlock System is also responsible for communicating the status of each system to the operators in the main control room. These operators will use the Central Interlock System to perform functionalities such as overrides, resets of central interlock functions and configuration of Plant Interlock Systems. Three different types of architecture have been developed: a slow one, based on PLCs, for functions for which response times longer than 300 ms are adequate, a fast one, based on FPGAs, for functions which require response times beyond the capabilities of the PLC, and a hardwired one to synchronise all the systems involved in a fast discharge of the superconducting coils. The overall design of the Central Interlock System was presented and approved for manufacturing in a Final Design Review in 2016.