Calorimeter Design for Neutral Beam Injector of DTT – Thermo-hydraulic Analysis

The main steps in the development of the calorimeter design for the Neutral Beam Injector (NBI) of Divertor Tokamak Test (DTT, a new tokamak whose construction is starting in Frascati, Italy) are presented. The beam power absorbed by the calorimeter panels is removed by the pressurized water flowing through the cooling pipes drilled into the panel structure. The heat transfer to the coolant is enhanced by twisted tape inserts. The design and dimensions of the panels and cooling pipes are based on the thermal-hydraulic optimisation using detailed Computational Fluid Dynamics (CFD) analyses. The analysis considers local thermal-hydraulic parameters, such as maximum temperature of the panels and of the coolant, coolant pressure drop and geometric constraints like panel inclination angle and available space. The beam power of the DTT NBI takes into account the beam imprints and power distributions in the beam core and in the beam halo, which are modelled by superposition of Gaussian functions. In CFD simulations the coupled solidfluid heat transfer problem is solved. Main design choices and optimisation are determined by minimising the maximum temperature of the panel structure and of the near-wall temperature of the coolant.