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A high-efficiency quasi-optical mode converter for a 140-GHz 1-MW CW gyrotron

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7 Author(s)
Thumm, M. ; Inst. fur Hochleistungsimpuls-und Mikrowellentechnik, Karlsruhe, Germany ; Yang, X. ; Arnold, A. ; Dammertz, G.
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A highly efficient quasi-optical mode converter system with several novel features has been designed and tested at Forschungszentrum Karlsruhe (FZK). The converter consists of a dimpled-wall waveguide launcher, one quasi-elliptical mirror and two toroidal mirrors. The coupled-mode theory has been used to analyze the operation of the prebunching waveguide launcher; the radiated fields from the cut of the launcher have been calculated by the scalar diffraction integral. Simulation results show that the advanced dimpled-wall launcher generates a well-focused Gaussian radiation pattern with low diffraction losses. In this case, toroidal mirrors are sufficient to obtain a desired output beam pattern. An efficiency of more than 98% has been achieved to convert the rotating TE28,8 cavity mode at 140 GHz into a fundamental Gaussian beam. Experimental measurements show close agreement with theoretical predictions.

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Electron Devices, IEEE Transactions on  (Volume:52 ,  Issue: 5 )