Comparative modeling of the coupling properties and the power spectra with different plasma densities and different phasing were performed for 2.45 GHz and 4.6 GHz waves respectively by using the ALOHA code. The modeling results show that the electron density for optimum coupling is ∼3 × 1017/m3 and ∼10 × 1017/m3 for 2.45 GHz and 4.6 GHz LH waves respectively. For both launchers the power directivity can be high as 76% and reflection coefficient less than 1% around the optimum density. When the density increases above the optimum value, the wave coupling becomes poor and simultaneously the power directivity decreases for both waves, hence reducing the current drive efficiency. However, the coupling property shows a lower sensitivity to plasma density for 4.6 GHz wave. By adjusting the phasing between main waveguides, the parallel refractive index (N//) can be varied from 1.7 to 2.5 for 4.6 GHz wave and from 1.9 to 2.9 for 2.45 GHz. It is found that the power directivity shows weak dependence on the phase difference between main waveguides for both of the waves. Comparison between ALOHA and experimental LH coupling results on EAST are presented. The power spectra with some modules powered off is also calculated. The results show that some lobes arise from left and right sides of the first main lobe for both of 2.45 GHz and 4.6 GHz waves.
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