The Lemon Hyperlens concept and its application to the DTT Neutral Beam Injector

The Divertor Tokamak Test facility (DTT), 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 [1]. The additional heating system includes a Neutral Beam Injector (NBI), providing fast deuterium neutrals (D0 ) with an energy of 510 keV and a maximum power of 10 MW. Due to size constraints and the peculiar multi-focus aiming strategy adopted by DTT NBI, the device required the development of novel concepts for particle beam steering. In this paper, we describe the concept underlying the newly adopted Lemon Hyperlenses Grids (LHGs): multi-curvature, lens-like electrostatic grids able to steer the beamlet array in the intended directions without shape deformation. The possible manufacturing through 3D Selective Laser Melting (SLM) printing and dimensional checking processes have also been investigated.