Study of the Hα emission of the SPIDER negative ions source

This dissertation assesses and compares plasma behaviour under different configurations of the plasma grid magnetic filter in the SPIDER experiment, part of the larger ITER project, through the study of the Hα emission of the hydrogen plasma. ITER is an international collaboration, involving the European Union, China, India, Japan, Korea, Russia and the United States, whose objective is to demonstrate the feasibility of fusion power generation through plasma magnetic confinement. A low density hydrogen plasma will be heated to about 1.5 · 108 K to start the nuclear fusion reaction. The project design will allow a self-sustaining process for long-duration machine runs (up to 1 h) to reach the 500 MW of fusion power output goal [1]. Many systems and subsystems are needed to reach such a high temperature: together with ohmic heating, thermal energy will be fed to the plasma via microwave radiation and neutral particle scattering, provided by two neutral beam injectors (NBI). The SPIDER ion source is part of the NBI system, providing up to 60 A current of H− ions extracted from a hydrogen plasma. Ions are then accelerated up to 100 keV and neutralised to obtain a high intensity neutral beam [2]. However, to achieve the required specification to ignite nuclear fusion and obtain the best power out- put, all systems need to achieve maximum optimisation. In the specific case of SPIDER, efficiency is achieved by maximising the spatial homogeneity of the neutral beam, which, in-turn, depends on the uniformity of the plasma produced in the source, which is required to deviate less than ±10% from ideal uniformity [2]. Many of SPIDER source components are still being tuned to solve stability and homogeneity issues, as well to increase the negative ions production. Thus, the study of the effects of the PG magnetic field topology on the produced plasma is of great interest to obtain the required data to improve plasma uniformity. In this dissertation, the SPIDER plasma source is introduced, along with the components of interest of this study, namely the plasma grid magnetic filter, in two topological configurations: a first prototype and a second improved one, and the plasma generators. Data analysis is then outlined presenting labelling, analysis roadmap and methodology. Finally, results assessment and description is conducted to lead to the final data comparison across different analysis methods.