Detection of thermo-mechanical deformations in tokamak bolometric systems using ray-tracing analysis of the diagnostic layout

Abstract Achieving controlled fusion necessitates the confinement of hot plasmas within devices called tokamaks, which use magnetic fields for this purpose. The accurate measurement of the total emitted radiation and impurities in these plasmas is crucial for optimizing performance and ensuring operational safety. Bolometers, which provide line-integrated measurements, are key diagnostics for measuring radiation. Tomography is essential in these measurements as it converts line integrals into spatial distributions, a process complicated by its inherently ill-posed mathematical nature. Traditional tomographic methods often approximate lines of sight as geometric lines; however, these lines broaden due to the geometry of the collection system and detectors, significantly affecting the accuracy of reconstructions. Enhancing the quality of these reconstructions requires a precise understanding of the viewing geometry. A comprehensive approach based on ray-tracing simulations is presented for calculating and validating geometric factors. By taking into account the detailed geometry of both the machine and the detectors, the method evaluates viewing factors and etendues while highlighting the sensitivity to thermal gradients and the impact of thermo-mechanical deformations on tomographic accuracy. It also provides guidance for optimizing complex aperture and collimator designs, without considering reflection effects, demonstrating its applicability and effectiveness for European tokamak scenarios.