Kinetic study of the secondary plasma created in the ITER neutraliser

The properties of the secondary plasma created inside the ITER Neutral Beam Injector (NBI) neutraliser, through the interaction of the high energetic hydrogen beam with the molecular hydrogen gas, have been analysed. Starting from the results of our OBI-2 PIC Monte-Carlo numerical code, detailed kinetic of the hydrogen plasma has been studied using a Collisional-Radiative model. In this model, the electron distribution function is determined by solving a Boltzmann equation, whereas main plasma species are derived from balance equations. This paper presents preliminary results obtained in a 0D geometry, boundary conditions bing introduced through effective rates for gain and loss of particles at the neutraliser walls. It has been found that the main ion specie is H2+, essentially coming from the ionisation of the target gas. The electron energy distribution function is not maxwellian and its mean energy is about 5 eV. The plasma-wall interactions yield a strong contribution, in particular regarding the density of molecular ion H3+. Assuming several independent slices of plasma along the negative ions beam axis, the axial profile of the secondary plasma has been analysed. It has been found that the density and mean energy profiles of the plasma electrons are directly related to the plasma potential profile, which in turn closely follows the gas density one.