Design of Mode-Selective Directional Couplers for ECRH on MFTF-B

摘要

The Electron Cyclotron Resonance Heating (ECRH) System will provide microwave energy at 28, 35, and 56 GHz to heat electrons in the thermal barrier and maximum potential regions in the end-plugs of the Mirror Fusion Test Facility (MFTF-B) tandem mirror machine. To design an effective quasi-optical antenna system for ECRH which will convert the TE/sub On/ output of overmoded circular waveguide to a linearly polarized collimated microwave beam requires an accurate determination of the modal content of microwave energy present in the overmoded circular waveguide. To determine the modal content in the waveguide system, mode-selective directional couplers have been designed and fabricated for the three ECRH operating frequencies. The directional couplers are designed to minimize mode conversions in the circular primary waveguide and to excite only the TE sub 10 mode in the overmoded rectangular secondary waveguide. The secondary waveguide is tapered in the large dimension down to fundamental TE sub 10 rectangular waveguide so conventional microwave components can be adapted to the directional couplers. (ERA citation 11:010695)