Coupling to Lower Hybrid Waves with the Multijunction Grill

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Abstract
Coupling characteristics of the multijunction grill have been studied in detail by experiments on the basis of a simple theory using a multireflection method with the aid of scattering matrices not only at the junction plane but also at the grill mouth. Theoretical values of the global reflection coefficients in the primary waveguide and secondary waveguides are estimated from the vector sum of reflecting components caused by each reflection between two scattering planes. The experimental results of scattering matrices and global coupling agree well with theoretically calculated ones. It is shown that the multiple reflection in secondary waveguides of the four-junction grill for the JIPPT-IIU tokamak is finished up to three or four reflections. The length of the secondary waveguide is confirmed to be one of the parameters determining the grill efficiency.