Electron density reconstruction and optimum beam arrangement of far-infrared interferometer in Heliotron J

Abstract

A multichannel far-infrared (FIR) laser interferometer is being developed for the helical-axis heliotron device Heliotron J with asymmetrical poloidal cross-section to study high-density plasma. Due to the shape of the crosssection, a new density reconstruction method based on the regularization technique was investigated for obtaining the electron density profile from the line-integrated density. For this purpose, the regularization parameter was optimized and determined by the generalized cross-validation (GCV) function and singular value decomposition (SVD). The reconstruction results show that the reconstructed profiles can be improved by carefully considering the beam position arrangement. The optimum beam arrangement is discussed in detail.