A quasi-optical mode converter with a bifocal mirror
- Thomson Tubes Electroniques, Velizy-Villacoublay (France)
The increasing demand for high-frequency, high-power microwave radiation for plasma heating in fusion experiments has pushed to the development of gyrotron oscillators operating in higher-volumic modes or even in whispering-gallery modes. Microwave generation in these modes imposes two serious problems: inefficient transmission and plasma heating due to wall losses and complex polarization. Therefore, the conversion of these modes into a low-order mode or into a Gaussian wave beam which then will propagate in free-space or in a corrugated waveguide as the HE{sub 11} mode, is absolutely necessary. This paper presents the design procedure of a quasi-optical mode converter to transform any kind of TE{sub mn} mode into a Gaussian wave beam and experimental results obtained in the particular case of the TE{sub 64} mode at 110 GHz. The quasi-optical system consists of a helical-cut launcher and a bifocal mirror, which is designed, using the techniques of geometric optics, to focus the radiation of the launcher into a Gaussian focal spot. Such a system was fabricated and tested for the transformation of the TE{sub 64} mode. The experimental results showed that about 80% of the power incident in the focal plane is focused into a small Gaussian-like spot of less than 20 mm diameter, while the 97% of the power is contained into the main TE{sub 64} lobe.
- OSTI ID:
- 46094
- Journal Information:
- IEEE Transactions on Microwave Theory and Techniques, Vol. 43, Issue 3; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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