3D tomography of Hydrogen and Helium plasma produced in the PROTO-SPHERA experiment

We propose an approach to image reconstruction based on a formulation of the Fourier slice theorem in 3D, which relates a set of projections onto planes -or 3D Radon transform- to a 3D Fourier transform. After a suitable transformation of coordinates, by calculating the 3D inverse Fourier transform of projections, the 3D image of the scanned object is reconstructed. The formulation is applied to the reconstruction of the distribution of light emission density of magnetically confined plasma, employing data provided by ENEA (Italian National Agency for Technology, Energy and Sustainable Economic Development). Data include light emission by Hydrogen and Helium plasma, recorded within the framework of the PROTO-SPHERA experiment, where plasma is produced within a transparent vessel and monitored by six cameras. This experiment displayed the appearance and sustainment of a plasma torus around an internal plasma centerpost by self-organisation; an entirely unexplored phenomenon to date. The 3D image reconstruction enabled observation of the formation of the plasma torus at different time instants and of the emission spectrum of its cross-sections.