Functional Analysis for the diagnostic systems to support the exploitation of the Divertor Tokamak Test facility

The technical studies for the realization of the Divertor Tokamak Test (DTT) facility are ongoing and with the progress of the design an increasing level of integration between the various systems and subsystems is required. In particular, it is difficult to define the structure of the diagnostics collection, because they have to meet very different needs to contribute to the machine operations. Known methodologies of functional analysis can assist in this task. The diagnostics functions can be divided in three high-level categories, possibly overlapping: normal operations control, physics research and machine/personnel safety protection. These functions can be mapped to the measured quantities involved, which must be formalized in terms of performance specifications. Finally, these requirements must be associated, in the framework of DTT Requirements Management and traceability, to the diagnostic systems which actually perform these functions, with a primary, secondary or backup role. This latter categorization depends on the operating states foreseen for the machine, taking into account possible degraded (or advanced) states associated to the most significant accidental conditions and which diagnostics can be affected by them. The traceability of these requirements to primary project functional requirements (each having a required availability) and the assignment of a different role in the measurements for the diagnostics gives the possibility to compute a preliminary estimation of the availability of the individual systems with the help of logical diagrams like Fault Trees. The application of this methodology throughout the design of DTT helps to choose an optimal set of diagnostics that meet the functions and constraints of the machine.