BTR application for beam slowing-down analysis

Abstract

BTR code, which is generally used for neutral beamline design and optimization, is applied to calculate the injected beam stopping in plasma, beam ionization and current drive in a fusion neutron source DEMO-FNS. The beam- plasma model implements detailed spatial and angular distributions of the injected beam taking into account the multi- channel injector geometry and operating parameters. The beam ionization incorporates the stopping cross-section fits by Janev-Suzuki. The beam's instant 3D deposition in a plasma is compared for various beam geometries. The beam losses and detailed shine-through images are obtained taking into account beam aberrations in the 3D plasma target. The fast ion current profiles are evaluated with a simple slowing-down procedure. The influence of beam size, beamlet focusing and inner divergence is proved to be essential for beam deposition and current drive efficiency. The aberrations of tangential beam decay in toroidal plasmas lead to beam profile asymmetry, which can be potentially critical for the current drive - especially when thick and divergent beams are injected off-axis.