Magnetic island temperature perturbation reconstruction in mixed second and third harmonic electron cyclotron emission conditions

The electron cyclotron emission (ECE) diagnostic is one of the prevailing methods to measure electron temperature in tokamaks. However, the ECE diagnostic is limited in a low toroidal field condition, where multiple ECE resonance layers exist in the plasmas. Because the resonance layers with different locations emit the same frequency waves, it complicates the estimation of spatially resolved electron temperature based on the wave frequency [1]. Here we present a technique to reconstruct the ECE signal associated with magnetic island perturbation in mixed multiple harmonic ECE conditions. The method utilizes the time dependence of magnetic island perturbations, which is absent in the other resonance layers, to extract the data. The attenuation of perturbations caused by the absorption in the other layers is also considered by calculating their optical thickness [2]. We successfully obtained the temporal evolutions of electron temperature perturbation profiles in the 2/1 magnetic island in mixed second and third harmonic ECE environments in the DIII-D tokamak.