3D tomographic reconstruction of light emission density of plasma in the PROTO-SPHERA experiment

We address a key challenge in plasma diagnostics: reconstructing the three-dimensional (3D) light emission density from projection data. To this end, we employ a method for reconstructing 3D density functions based on a corollary of the 3D Fourier slice theorem. This corollary establishes a connection between 2D plane projections and plane sections of the 3D Fourier transform, enabling a direct and non-iterative solution to the inverse problem. The method is applied to the PROTO-SPHERA experiment, an innovative magnetic confinement plasma setup for controlled nuclear fusion research. Experimental data were acquired using six high-speed cameras arranged with cylindrical symmetry around the plasma chamber, capturing time-resolved pictures that are assumed to be parallel projections of the visible light emissions from Helium and Hydrogen discharges. After a transformation of coordinates, by computing their inverse 3D Fourier transform, we reconstruct the spatial distribution of light emission density. This technique enabled to reveal dynamic features of plasma self-organization — such as torus formation around a centerpost — and provides internal cross-sectional views of the plasma, displaying previously obscured spectral components.