Visible Light Tomography Considering Reflection Light in a Small Tokamak Device PHiX

In a small tokamak, the visible light emission is observed and used to investigate plasmas' behavior with a fast visible camera. However, the reflected light causes a systemic error in measuring visible light emitted from the plasma. In this paper, we managed to overcome the reflection effect with the ray-tracing technique which is utilized in a synthetic diagnostic platform of the small tokamak device PHiX at Tokyo Institute of Technology using Raysect and CHERAB python libraries. We successfully evaluated the amount of reflected light and obtained tomographic reconstruction images from simulated and experimental data with the Tikhonov-Phillips regularization and the L-curve method to choose an optimal regularization parameter. We also proposed to project the contour of a reconstruction image onto a camera image to validate tomography results. (C) 2021 The Japan Society of Plasma Science and Nuclear Fusion Research