Conceptual design and main requirements of the divertor tokamak test (DTT) cryogenic system

• DTT cryogenic system requires a cryogenic capacity of approximately 10 kW at 4.5 K. • Optimized cooling strategy to implement multi-temperature level helium distribution. • Variable heat loads and changeable operational states to be handled. The Divertor Tokamak Test (DTT) facility ( https://www.dtt-project.it/ ), currently in initial phase of construction at the ENEA Frascati Research Centre, is designed to explore critical components of tokamak, such as the divertor, in plasma regimes that are relevant for ITER and DEMO (as far as power loads are concerned), and where plasma core and edge properties are fully integrated. To achieve this goal, considerable amounts of plasma heating will be injected in DTT, whose ambitious program is spread over several years and different operational phases. The DTT facility is designed to produce sufficiently long plasma pulses, thus requiring the adoption of a superconducting magnet system. This latter includes 18 Toroidal Field (TF) coils, 7 Central Solenoid (CS) modules and 6 Poloidal Field (PF) coils. All superconducting coils are supported by a cold structure with thermalized gravity supports and thermally protected in a cryostat with actively cooled thermal shields. The coils and their structures need to be cooled by supercritical helium supplied at about 4.5 K. The thermal shields (TS) have to be cooled with pressurized helium at 80 K. The superconducting coils are connected to the power supply by means of superconducting feeders which need to be maintained at around 4.5 K. High Temperature Superconducting (HTS) current leads (CL), which operate between ambient and cryogenic temperatures, require cold helium gas flow at 50 K. To allow helium and hydrogen adsorption, cryopumps behind the divertor targets are employed, requiring two cryogenic helium streams, one at around 4.5 K for the cryopump panels and one at 80 K for cryopump baffles. The Cryogenic System has to cool-down the cryogenic users and to keep them at their design temperatures during different operation modes and plasma scenarios. The overall cryogenic capacity is estimated to be around 10 kW equivalent power at 4.5 K. This paper gives a general overview of the Cryogenic System requirements, the proposed conceptual design, and a description of the main layout.