Effects of polarization change on the measurement of electron temperature profile from ECE in tokamak plasma

In order to investigate the effect of polarization change on measurements of electron temperature profile from electron cyclotron emission (ECE) in a tokamak plasma, we have calculated the spatial evolution of the electric field of ECE propagating in the plasma. In the case of almost on-axis propagation, the Boyd's prediction is a good approximation, that is, the electric vector rotates with magnetic field. On the other hand, along horizontal sight line far from the axis the Boyd's prediction has a discrepancy of 3% from the numerical results. The effect of the polarization change is important for the measurement of ECE imaging in large tokamaks.