QUASI-OPTICAL GRILL MOUNTED IN HYPERGUIDE

A proposal for a new lower hybrid wave launcher for the current drive in future large thermonuclear facilities operating in the 10 GHz frequ ency range is given. The principle of the quasi-optical grill is combi ned with the concepts of the hyperguide and the multijunction grill. A s an example, a six rod structure mounted in an oversized waveguide an d irradiated by an oblique plane wave emerging in the form of a higher mode from an auxiliary oversized waveguide is optimized. The rods of the optimum structure have the elongated form of the cross-section wit h a resonant length (in the direction of wave propagation) equal to a multiple of the half wavelength of the fundamental mode of the hypergu ide. This row of rods forms a multijunction grill with the zero, built -in, phase shift between waveguides. The second row of rods supporting the constructive superposition of the incident and doubly reflected w aves enhances the efficiency of the structure. The optimum structure h as a power spectrum with two narrow peaks (the main N-parallel to = -2 .15 peak and the parasitic N-parallel to = 3.15 peak), a low power ref lection (R-tot = 18%), a high coupled power directivity (delta(CP) = 6 8%), a reasonable N-parallel to-weighted directivity (\delta(CD)(w)\ = 36%) and a peaking factor on the electric held equal to 3. On the bas is of the optimization it is possible to design the parameters of a la rge structure with tens of rods. The number of construction elements i n this structure can be reduced 20 times in comparison with the standa rd multijunction array.