Preliminary design and thermal analyses of the steerable mirror cooling channel of the DTT ECRH

Divertor Tokamak Test (DTT) facility, the Italian fusion machine, foresees the Electron Cyclotron Resonance Heating (ECRH) system to provide additional heating power to plasma ohmic-heating. Such system will be composed of an initial set of 8 mm-wave 1-MW sources at 170 GHz, which will be raised to 16 in a second stage of installation. The power of each source will be launched into the plasma by a pair of mirrors in the port plug, while a series of mirrors is used for the transmission of microwave beams. They are subjected to microwave heating load and the mirrors closest to the plasma also to radiative and neutronic loads. In order to avoid a performance loss of the beam transmission, due to the deformations, caused by the increment of temperature on the mirrors, it is necessary to design a cooling circuit inside them. This paper aims to make a preliminary design, using FEA tools, of the cooling circuit in the steerable mirror (M2) of the ECRH Launcher. A thermal analysis was performed to study how geometrical and thermal choices can influence the dissipation of the heat and the maximum temperatures of the structure. First of all the best geometric configuration was individuated: a cooling circuit dug in the mirror with a shape of an elongated spiral with constant pitch on y-axis and the inlet not centred in the origin. Starting from this geometry, parametric analyses were carried out to establish the correct ranges of applicability and study the influence of the inlet temperature and the volume flow rate of the refrigerant fluid on the temperature of the mirror. The simulations confirmed the theoretical expected thermal trends, but also that the preliminary tested values of the input parameters could be used to realize an efficient cooling for the structure. The analyses are set up within ANSYS environment, on the basis of the provided data and constraints.