Tomography of divertor neutral particle emission using visible CCD imaging under metal-wall condition in EAST

Abstract The two-dimensional distribution of neutral particles in the divertor region is essential for a comprehensive study of tokamak scrape-off layer and divertor physics. Recently, EAST has been equipped with a high-resolution, tangentially viewing visible camera system. This system enables the reconstruction of the poloidal cross-section distribution of D α emissions around the divertor area through a tomographic method, utilizing the visible images it captures. In this work, we introduce an analytical approach to calculate the geometry weight matrix during the tomographic reconstruction process, significantly enhancing both the accuracy and speed of the reconstructions process. The impact of visible light reflection from metal walls on the reconstruction result is also considered. It has been found that the application of a micro-facet model can effectively mitigate these reflections’ effects. Furthermore, the Simultaneous Adaptive Algebraic Reconstruction Technique has been employed to boost the efficiency of the reconstruction process. These methodologies were applied to analyze the characteristics and evolution of divertor D α emissions during a typical long-pulse H-mode experiment conducted without lithium coating. Additionally, preliminary benchmarks comparing tomographic reconstruction results with simulations from SOLPS-ITER are also included.