Comparison of Neutral Beam Injection options for EU DEMO pulsed scenario

Neutral Beam Injection (NBI) is one of the methods being considered to provide auxiliary power and current to DEMO plasma. A new concept of neutral beam (NB) injector has been recently proposed with the aim of improving the system and maximiz ing the overall efficiency [ 1 ]. The design considers several innovative solutions, mainly regarding the beam source, the neutralizer (with the integration of a photoneutralizer) and the vacuum pumping system. T he se new solutions require an uncommon beam shape ("thin and tall") and t h e new injector is supposed to deliver neutral particles at 800 keV energy . Th e present work is intended to complement previous technical studies by numerical simulations of beam - plasma interaction for the reference flattop scenario of the puls ed EU DEMO [2] in order to understand the impact of the new NBI concept . To understand the effect of the design choices in a wide parameter range, t he first part of the current work deals with a parametric scan performed using a simplified NBI geometry by means of the fast tokamak simulator METIS (0.5D). The new NBI concept is also compared with an ITER - like NB injector. To deepen the analysis, detailed Monte Carlo simulations of NBI into stationary plasma have been run by means of the BBNBI ionization code and the orbit - fol l ow ing ASCOT code . The real NB beamlet geometry has been implemented for two different injection angles and beam focus es . Results on NB ionization, fast particle losses , power deposition and driven current are compared and discussed. The results confirm the effectiveness of the new NB I concept also from the point of view of DEMO plasma scenario integration.