Effects of Relativistic Frequency Down-Shift and Optical Thickness on Measurements of Electron Temperature Profile from Electron Cyclotron Emission in Medium Temperature Tokamak Plasmas

The importance of the relativistic frequency down-shift and the optical thickness is pointed out in the determination of the electron temperature profile from electron cyclotron emission (ECE) measurement in the medium electron temperature region. These effects cause a pseudo radial displacement (Δ r ) of the obtained electron temperature profile. The pseudo displacement depends on only three parameters (the electron temperature, T e , the optical depth, τ, and the major radius, R ). In order to correct the radial position in any tokamak, a scaling law of the displacement is derived as Δ r ( m)=0.0009 R (m) T e (keV) (1+40/(5τ)). This scaling law is applicable to the plasma with τ>5 where the error is less than 0.5% of the major radius.