  The Beam Driven Plasma Neutralizer (BDPN) has been proposed as a more
efficient alternative to the gas neutralizer for negative-ion based Neutral
Beam Injection (NNBI). In this paper we model the performance of an entire NNBI
beamline with a BDPN. We simultaneously consider all the relevant physics and
engineering aspects, the most important being the plasma density and degree of
ionization inside the BDPN as a function of its geometry and feed gas flow, the
geometrical transmission of the beamline, the dependence of the neutral gas
distribution in the beamline on the geometry of the beamline components and gas
flows, and the species evolution of the extracted D$^-$ beam through this
neutral and charged particle distribution. Furthermore, we calculate the heat
loads expected on the BDPN parts and on the NBI components located downstream
of it and study the effect of the magnetic cusp field across the BDPN entrance
on beamline transmission. While our results constitute an optimization only
under the applied boundary conditions, we find that the beamline with a BDPN
increases the system's wall plug efficiency by about 13% to 0.34 from the 0.30
estimated for a gas neutralizer.
