The Spherical and Lemon Hyperlens Grids Concept Applied to the DTT Neutral Beam Injector

The Divertor Tokamak Test (DTT) facility, currently under construction in Frascati (Italy), will be devoted to studying the main issues related to power exhaust in fusion facilities, under integrated physics and technical conditions relevant for ITER and DEMO. The additional heating system includes a neutral beam injector (NBI), providing fast deuterium neutrals (D
$^{0}$
) with an energy of 510 keV and a maximum power of 10 MW. Due to size constraints and the peculiar multifocus aiming strategy adopted by DTT NBI, the device has required the development of novel concepts for particle beam steering. In this article, we describe the concept underlying the newly adopted spherical and Lemon hyperlens grids (SLHGs): multicurvature, lens-like electrostatic grids able to steer the beamlet array in the intended directions without shape deformation.