The impact of the edge density fluctuations on the electron cyclotron wave propagation in tokamaks*

In this work we show a numerical analysis of the electron cyclotron (EC) wave beam propagation in the presence of the edge density fluctuations for DIII-D-like and ITER-like plasmas. Particular attention will be paid on the broadening of the EC beam at the EC resonance location with and without edge density fluctuations. In fact, such broadening might affect the ECCD efficiency to suppress the neoclassical tearing mode (NTM) instability particularly for ITER plasmas where the distance between the SOL density fluctuations and the EC resonance is larger than one meter. In this paper we make use of a 2D/3D code originally developed for reflectometer simulations. This code was extensively used for reflectometer antenna-plasma coupling calculations that include density fluctuations. One important capability of the code is that the numerical domain can be divided in three regions: a vacuum region, a paraxial region, and a full-wave region, for high computation efficiency. A scan in the amplitude of edge density fluctuations will be performed together with the evaluation of the 3D electric field pattern at the location of the EC resonance. The importance of these results on NTM suppression by ECCD on ITER will be discussed.