Plasma interface of the EC waves to the LHD peripheral region

In order to realize an efficient ECRH and also to reduce stray radiation due to non-absorbed power during ECRH, it is necessary to excite a wave that is absorbed well near the electron cyclotron resonance. In the normal fusion magnetic field confinement machine and in the electron cyclotron frequency range, WKB approximation is valid almost all the way from antenna to the absorption region due to the large scale-length of the plasma density λ_n and the magnetic shear τ_s as compared with the local wavelength λ₀. In these situation, it is well known that the O/X mode propagates as O/X mode if τ_s ≫ λ₀. Even in these situation, if τ_s and λ_n are comparable and |1/λ_O−1/λ_X|τ_s ≪ 1, there still remains the question from where "X" - or "O" - mode become "X" - or "O" mode at the peripheral region. In order to simulate this situation, one dimensional full wave calculation code which solve electromagnetic wave equation under arbitrary magnetic field configuration and arbitrary density profile for a given polarization state are developed and incorporated in the upgraded ray tracing code LHDGauss. It is tried to find the density and shear scale lengths region where the mode mixing effect is not negligible