Development of a collisional-radiative code for the interpretation of optical emission spectroscopy measurements in a helicon plasma source

Optical emission spectroscopy (OES) is a non invasive diagnostic tool for the the characterization of a plasma source. In order to interpret the data from these measurements, it is necessary to take advantage of a collisional radiative code that, starting from the light emitted by the plasma source, can translate this information into plasma parameters. The goal of this work is the development of a collisional radiative code, AtoH, for the interpretation of visible spectrum of hydrogen plasma discharges performed at the resonant antenna ion device (RAID). The first step of the project is the realization of a code that, starting from known plasma conditions, is able to estimate the population density of the excited states of atomic hydrogen, and therefore the emissivity. Then, the results of these simulations are compared with emissivity estimated by Yacora, a web application for the simulation of atomic hydrogen spectral lines. This comparison showed that the two codes differ, and this is probably due to the different number of quantum states of hydrogen taken into account in the models, and to the different collisional data. Subsequently, the OES campaign carried on in RAID is described and the main results are reported and commented. Finally, AtoH is used for the interpretation of the measurements and for the investigation of the effect of negative ions on the line ratio. Use a collisional radiative code for the OES interpretation means find the plasma parameters combination that reduces the difference between the experimental emissivity and the theoretical one. The result is that, even if AtoH has some limitations, it give as output a good approximation of plasma parameters. However, many improvements can be done on AtoH, and they could be the basis for future work, especially the increment of the number of quantum states and the addition of more collisional channels.