Improved design for Heliotron J soft X-ray diagnostic for tomographic reconstruction studies

Abstract

Identifications of the plasma boundary shape and mode structure are important problems for the studies of the magnetohydrodynamics equilibrium and stability studies. Imaging diagnostics have the possibility to measure the plasma boundary shape and mode structure directly. The soft X-ray (SX) tomography is an imaging diagnostic for offering these direct measurements. However, SX tomography is by nature a limited angle tomography and provides a challenge as an ill-condition inverse problem. The reconstructed profiles depend heavily on the quality of measurements along with the employed inversion algorithm. This paper provides a detailed description of tomographic reconstruction of simulated SX measurements from the current SX diagnostic design of Heliotron J (H-J), which is a medium size heliotron device. Heliotron J has a unique magnetic geometry, and the quantitative identification of the plasma boundary and mode structure is a critical problem. The Phillip-Tikhonov regularization is employed to address the inversion problem. Finally, a new design for Heliotron J soft X-ray diagnostic is discussed which holds enhanced capabilities for tomographic reconstructions especially for the high poloidal number perturbations.