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 timeresolved 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.