Impact of the Plasma Boundary on Machine Operation, and the Risk Mitigation Strategy on JET
This work examines the separatrix and SOL characteristics in three scenarios on JET: the Quasi-Continuous Exhaust (QCE) regime, the core-edge-SOL integrated ITER Baseline scenario, and the X-point Radiator (XPR) regime. All three scenarios are potentially compatible with reactor operations, as they aim to provide power exhaust solutions through different approaches. The QCE regime is distinguished by its generally higher separatrix and SOL collisionality, associating with broader SOL width. These features, combined with the near-double-null (DNX) configuration, introduce several operational challenges on JET. The resulting broader SOL width interact with fast Beam neutrals, contributing to an unfavourable power load on local limiter. Additionally, the heat load on the Upper Dump Plate Tiles (UDPT) and outer limiter in the QCE regime can be up to 5–6 times higher compared to the other scenarios. However, through careful operational planning and robust real-time protection system, the power loads were effectively managed within acceptable limits during QCE pulses, enabling successful scientific outcomes. As a result, the QCE regime serves as a case study to illustrate the critical need for integrating physics understanding, risk identification, operational strategies, and robust real-time protection to successfully implement new scenarios for fusion devices.