We discuss the tunneling of quasi-optical wave beams through the evanescent region near the plasma cutoff in magnetized plasmas with density fluctuations. A model is proposed that describes the effect of a random modulation of a wave phase induced by the fluctuations along the propagation path on the efficiency of linear coupling between the ordinary and extraordinary waves in a two-dimensional geometry that suits well the toroidal magnetic systems. An analytical formula is derived that relates the averaged coupling efficiency and the phase correlation function of a random wave beam. Thresholds are found for the correlation length of the random phase and the length of the beam path, above which the density fluctuations become the dominant effect, and the importance of two-dimensional effects is shown. The analytical results are verified with full-wave numerical calculations.
Coupling of fast waves launched into the JFT-2M tokamak by a phased four-loop antenna array