Conceptual design of DTT magnetic diagnostics

Abstract

The Divertor Tokamak Test (DTT) is a new tokamak device whose main mission is to explore innovative divertor concepts for DEMO and test them in heat loads conditions on plasma facing components relevant to a fusion reactor. The device is presently going through a detailed design process, and the tendering process has started for some of the components. Magnetic diagnostics for plasma current and shape control, and vertical position stabilization are essential diagnostics for tokamak operation, and are the first diagnostic components that will need to be ready for installation and commissioning when DTT vacuum vessel and magnets are assembled. The DTT operational conditions for in-vessel and ex-vessel magnetic diagnostics resemble those that will be encountered in ITER (high heat flux, long pulses, large Electromagnetic stresses), except for the 14MeV neutron effects. Furthermore the compact machine assembly implies a very tight space for High Field Side sensors, both in-vessel and ex-vessel, therefore a dedicated thin sensors design is mandatory. In this work the conceptual design of DTT magnetic diagnostics will be presented, including Mirnov Coils, LTCC coils, saddle loops, flux loops and diamagnetic loops, Hall probes and optic fibre plasma current measurements. The constraints that have been taken into account in choosing the sensors technology will be outlined, motivating the different design choices. Sensors number and sensitivity have been determined with a model-based optimization procedure: the error in the reconstruction of plasma current and current centroid position has been iteratively estimated by varying the placement of a current filament on a grid spanning the vacuum vessel volume. The maximum reconstruction error has been evaluated for different sensors number, position and effective area (NA). The optimal sensors setup will be discussed, in order to keep the error in plasma current less than 1%, and the error on the current centroid position less than 1cm. Finally the difficult task of integrating the sensors design with the machine first wall and vacuum vessel design will be discussed.