Performance optimization of the electrostatic accelerator for DTT Neutral Beam Injector

The main purpose of the Divertor Tokamak Test facility (DTT) is to study alternative solutions to mitigate the issue of power exhaust under integrated physics and technical conditions relevant for ITER and DEMO. DTT will be equipped with a 510 keV, 40 A Neutral Beam Injector (NBI) based on negative deuterium ion particles, designed to yield about 10 MW of neutral power to the DTT tokamak. The strongly triangular shape of the beam and the ITER-like multi-focusing strategy required a different approach than more conventional solutions in designing the electrostatic plates in order to guarantee the desired beam deflection. This paper describes the performance optimization process carried out for the injector of the DTT NBI system. In particular, a new electrostatic design concept for the accelerator grids has been implemented, the Hyperlens Grids: additional grids with a lens-like profile, imparting to each separate beamlet the necessary exit deflection without shape deformation.