Abstract
Abstract
DEMO-FNS (DEMO Fusion Neutron Source) will be a hybrid reactor designed to combine fusion
and fission technologies. In a hybrid reactor the power is mainly produced by a fission blanket
which is exposed to the neutron flux generated by confined fusion plasma used as a Fusion Neutron
Source (FNS). The steady-state operation of the FNS is easier to achieve as compared to pure
fusion reactors, allowing the FNS to be more compact. The DEMO-FNS will produce 40 MW of fusion
power. The neutral beam injectors (NBI) are designed to provide a steady state plasma heating,
rotation, fueling, current drive and neutron generation in DEMO-FNS. Four injector units will
deliver 30 MW power in deuterium with energy Eb
= 500 keV. The NBI concept and main components
are inspired from ITER HNBI design implementing acceleration of negative ions with their
neutralization on gas.
The high density of injected power in DEMO-FNS leads to a very specific operation scenario with a
higher ratio of high-energy ions in the plasma with respect to conventional tokamaks, where the main
part of neutron flux will result from fusion between hot-tail ions and relatively cold
background. The current drive and neutron yield produced by the tangentially injected beam in a
steady-state operation are strongly affected by magnetic configuration and plasma kinetic
profiles. The fast ions deposition and performance in plasma are limited by the losses associated
with the neutral beam shape and aiming. The main channels of direct beam losses include
shine-through losses, as well as fast ion orbital losses. The detailed evaluation of NB parameters
and geometry effects is a necessary step of scenario optimization.
BTR code (Beam Transmission or, in earlier versions, Beam Transmission with
Reionization) is intended for injector beamlines study, and BTR detailed beam model can be also
applied to perform a detailed analysis of beam losses and performance in plasma. The analysis of
beam in plasma shows the ways towards higher values of beam driven current (NBCD) and neutral
yield; the beam-in-plasma behaviour can be tuned for a given tokamak configuration. The NB tracing
model workflow is implemented in the BTOR suite (Beam in TORoids). The results for DEMO-FNS
are compared with the NBI performance in ITER tokamak, as both machines are beam-driven and
implement a similar NBI concept.