Study of the production mechanisms of hydrogen (H-) and deuterium (D-) negative ions in continuous and pulsed microwave plasmas through complementary diagnostic techniques ; Etude des mécanismes de production d'ions négatifs d'hydrogène (H-) et de deutérium (D-) en plasmas micro-ondes continu et pulsé par des diagnostics complémentaires

Hydrogen negative ion sources are integral components in modern accelerator facilities and in the Neutral Beam Injection (NBI) systems of future fusion reactors. The latter application necessitates the development of such very powerful sources and the extension of their operation to deuterium. Numerous research activities on laboratory-scale experiments have been devoted to this subject aiming at understanding the fundamental processes that govern negative ion production. The gained knowledge has contributed essentially to the development of the prototype sources that will be employed in the NBI system of ITER, the largest Tokamak reactor under construction which is foreseen to demonstrate the potential of exploitation of thermonuclear fusion as an alternative source of energy. Nonetheless, there are important technological issues arising from the fundamental physics underlying these sources which need to be overcome in order for them to be able to deliver neutral beams with characteristics satisfying the baseline requirements.In the present thesis, the production of hydrogen (H-) and deuterium (D-) negative ions is studied in Electron Cyclotron Resonance (ECR) driven plasmas. In particular, experimental studies have been carried out in two reactors of similar characteristics, namely “Prometheus I” and “SCHEME-II+”, by means of conventional and state-of-the-art diagnostic techniques tailored to investigate the macroscopic and atomic properties of the plasmas of the two isotopes. In these reactors, negative ion production is based on the so-called volume production mechanism. In this case, the Dissociative Electron Attachment (DEA) reaction is identified as the predominant one. Understanding those factors which influence this reaction may lead to its control and thus an even better control of the negative ion production.In the “Prometheus I” reactor, parametric studies in hydrogen and deuterium plasmas as a function of the supplied microwave power and working gas pressure reveal the existence of optima for ...