The superconducting tokamak JT-60SA, under construction in Naka (Japan), is a device which will study advanced plasma conditions, such as steady state scenarios and break-even equivalent plasmas . The machine will start its operation with a carbon wall, where the plasma-facing components are CFC tiles.
The additional heating system relies on a flexible combination of Electron Cyclotron and Neutral Beams (NBs). The beam injection system is composed of 12 neutral beam units with positive ion sources (P-NB) providing 2 MW each and two negative ion sources units (N-NB) providing 5 MW each, for a total power of 34 MW.
In this work, NBI (Neutral Beam Injection) simulations are carried out using BBNBI (Beamlet-Based Neutral Beam Injection model) and ASCOT (Accelerated Simulation of Charged Particle Orbits in a Tokamak) codes . BBNBI is a Monte Carlo code to simulate the ionisation of fast particles injected through NBs, while ASCOT is a Monte Carlo code that solves the Fokker-Plank equation combining guiding centre and full particle gyro-motion.
The effect of carbon in the plasma for NBI will be shown. The presence of C changes the position of the neutral particle ionisation, giving a higher fast ions birth profile in the plasma edge. The ions position has a strong effect on the particles slowing-down, changing the power, current and torque deposition profiles. In addition, particles losses can be enhanced and the presence of different plasma species influences the aforementioned quantities too. The differences in the cases studied can reach up to 50% in the outer side of the plasma.
It is possible to study injection energies different from the designed ones (85 keV for P-NB and 0.5 MeV for N-NB). By changing the power (i.e. the acceleration grid potential), some assumptions on the power should be taken into account since they are not independent. In this work we assumed a constant perveance, thus P~E5/2.This affects the deposition profiles (due to the different cross-sections) and the orbit losses, which are strictly related to the particles velocity. Injection energy modulation results in different coupling to background plasma particles, in particular higher power is ceased to ions instead of electrons, driving less plasma current. Distribution function of particles gets highly modified by the modification of injection energy and this is relevant for interaction between fast particles and magnetohydrodynamic modes.