Study of H- production in H2 microwave multipolar plasmas by optical and electrical diagnostics

A way to achieve heating is the injection in the plasma of highly energetic particles (∼ MeV) that will transfer their energy during collisions. For this purpose, energetic charged particles are independently created in D2 plasmas and then neutralized so they can penetrate into the tokamak without being sensitive to the magnetic confinement. Neutral beam injection can deliver up to 16 MW into the ITER plasma. D- beams are used rather than D+ as the neutralisation of the latter is almost zero instead of 60% for D-, at the energy of interest. In this framework, our work is devoted to the production of H- negative ions from H2 microwave multi-dipolar plasmas. Negative ions are produced inside the plasma volume by dissociative electron attachment to highly vibrationally-excited molecules H2 (step 3). They can also be produced throughout plasma-surface interactions, where H atoms created in the plasma volume stick on the material (step 1) and recombine with hydrogen present on the surface, resulting in the desorption of a vibrationally-excited H2 molecule (step 2), which reacts with a cold electron to form a negative ion (step 3). Plasma diagnostics are implemented to better understand the mechanisms involved in H production. Step 3 is studied by means of Langmuir probes for electron density and energy distribution measurements, while laser photo-detachment (Nd-YAG, 1064 nm) gives negative ion densities. H atom densities are followed by Optical Emission Spectroscopy (OES) using actinometry, as well as Laser Induced Fluorescence with one (LIF) or two (TALIF) photons. By generating H atom spatial profiles via Abel transform, we try to differentiate volume mechanisms from surface ones. This document is composed of a short paper followed by a poster