Design study of 3-D tomography diagnostics for spherical tokamaks

Abstract:

A novel three-dimensional (3-D) tomography software has been developed for spherical tokamak (ST) plasmas with thin central coils. It enables us to measure whole 3-D annular profiles of ST plasma emissivity (line spectrum etc.) using limited number of detectors located on a sphere outside of its separatrix. The numbers and positions of detectors have been optimized for STs that contain low-n toroidal modes from n = 1 to 5. Mathematical method allowing for the removal of the thin central coil from the region of reconstruction and to reconstruct STs with single and double axes are also discussed. The shadow effect of center coil region was found to limit the reconstruction accuracy, indicating that the low-aspect ratio torus (ST) is essential to this new 3-D tomography diagnostics.