Tomography of a simply magnetized toroidal plasma

Abstract

Optical emission spectroscopy is a passive diagnostic technique, which does not perturb the plasma state. In particular, in a hydrogen plasma, Balmer-alpha (H α) emission can be easily measured in the visible range along a line of sight from outside the plasma vessel. Other emission lines in the visible spectral range from hydrogen atoms and molecules can be exploited too, in order to gather complementary pieces of information on the plasma state. Tomography allows us to capture bi-dimensional structures. We propose to adopt an emission spectroscopy tomography for studying the transverse profiles of magnetized plasmas when Abel inversion is not exploitable. An experimental campaign was carried out at the Thorello device, a simple magnetized torus. The characteristics of the profile extraction method, which we implemented for this purpose are discussed, together with a few results concerning the plasma profiles in a simply magnetized torus configuration.

A spectroscopical study of H$$_{2}$$ emission in a simply magnetized toroidal plasma

“…The light emitted from the plasma could be collected from the windows placed in the sector junction opposite to the filament location (see Fig. 1), from which the full poloidal cross section can be viewed [7]. A set of 19 viewlines was implemented, with structures fitting to the window shape, allowing to collect light with an optical fiber in an easy but reproducible way (see Fig.…”

“…A 800-μm, UV-enhanced optical fiber from Avantes was used to bring the light collected from the viewlines to the spectrometer. Viewlines spectra can be analyzed separatedly, but the whole dataset allows to reconstruct a 2D map of the plasma average emissivity, covering the poloidal cross section with a rough mesh of hexagonal cells with a resolution of about 3.5 cm [7]. To reduce statistical uncertainty, we measure three times the full set of 19 viewlines, each set with a different random order, to mitigate effects due to plasma fluctuations as well as plasma parameters drift.…”

“…However, even in a simple hydrogen lowtemperature plasma, OES reveals many features arising from the complex plasma gas phase. Although atomic hydrogen dominates emission, it is common to spot emission also from the rich structure of excited levels of the H 2 molecules [7]. Such features in the emission spectra are suitable to study particular phenomena happening in the plasma, be it those arising due to presence of minority ions, the recombination or the dynamical effects induced by the collisions with neutrals [8].…”

Spatially resolved determination of the electronic density and temperature by a visible spectro-tomography diagnostic in a linear magnetized plasma

“…The obtained results are in good agreement with the Langmuir probe ones.Spectro-tomography combines the advantage of these two approaches to simultaneously offer spatial and spectral resolution. This method provides 2D maps of light intensities at different wavelengths [12], giving access to the plasma electronic density and temperature.The experimental set-up and the tomographic method are presented in section 2 and 3, respectively. The experimental results are detailed in section 4 with 3 sub-sections: Experimental confirmation of the corona equilibrium in Mistral,  Validation of the spectro-tomographic results,…”

“…Spectro-tomography combines the advantage of these two approaches to simultaneously offer spatial and spectral resolution. This method provides 2D maps of light intensities at different wavelengths [12], giving access to the plasma electronic density and temperature.…”