Analysis of asymmetry of the D α emission spectra under the Zeeman effect in boundary region for D–D experiment on EAST tokamak*

Abstract

In 2015 campaign, deuterium atomic emission spectra (D α ) under the Zeeman effect in boundary region had been measured by a high resolution optical spectroscopic multichannel analysis (OSMA) system based on passive spectroscopy during the deuterium plasma discharge on EAST tokamak, and part of the works about the Zeeman effect on D α spectra had already been done. However, the asymmetric phenomena of D α emission spectra under the Zeeman effect were observed in process of analyzing the spectral data. To understand the asymmetric phenomena and acquire the useful local plasma information, an algorithm was proposed and used to analyze the asymmetry of the emission spectra under the Zeeman effect with all polarization components (π and ±σ). In the algorithm, the neutral atoms were considered to follow the Maxwell distribution on EAST, and I +σ ≠ I −σ was considered and set. Because of the line-averaged spectra along the viewing chord, the emission spectra were considered from two different regions: low-field side (LFS) and high-field side (HFS). Each spectral line was classified into three energy categories (the cold, warm, and hot) based on different atomic production processes in boundary recycling. The viewing angle θ (between the magnetic field B and the viewing chord), magnetic field B at two spectral emission positions (HFS and LFS) and the Doppler shift of all three energy categories of each spectral line were all considered in the algorithm. The effect of instrument function was also included here. The information of the boundary plasma were acquired, the reason for the asymmetric phenomena was discussed, and the boundary recycling during the discharge were studied in the paper. Based on fitting a statistical data of acquired fitting results, an important conclusion was acquired that the ratio of the spectral line intensity in HFS and LFS was proportional to the square of that of the corresponding magnetic field.