EU-DEMO limiters design integration issues and constraints driven by remote maintenance challenges

The Limiter (LIM) System of a port-based tokamak like the EU-DEMO encompasses different kinds of limiters for first wall protection purposes. Although the limiters’ position and poloidal surface extension are driven by plasma physics inputs and verified under charged particle heat loads by means of field line tracing, they should also be designed to be easily and independently handled through vacuum vessel ports. Among the four identified types of limiters, four Outboard Lower Limiters (OLL) and four Inboard Midplane Limiters (IML) – when the inboard protection is conceived as a standalone component – do not have dedicated ports for their maintenance, as no vacuum vessel openings are foreseen in the lower outboard first wall, precisely behind the OLL, and behind the IML in the inboard equatorial first wall. On one hand, limiters should be designed to protect the first wall against energy depositions following plasma disruptive events; on the other side, though, it is important to ensure that the protection system is designed under realistic constraints to be easily handled and realistically maintained. Therefore, integration and remote maintenance requirements and needs become an important factor affecting both the OLL and IML integrated engineering design, for which a dedicated handling strategy becomes one of the main drivers, together with physics needs. The paper presents the rationale followed for addressing the integration issues which drive the design of limiters with no dedicated ports behind them, and the remote maintenance strategy supporting their design concept. The definition of the handling strategy will help identify robust design drivers that apply to the entire lifecycle of the OLL and IML and improve the feasibility of achieving a practicable design solution compatible with its remote maintenance at every stage.