THE DESIGNS OF HIGH EFFICIENCY LAUNCHER OF QUASI-OPTICAL MODE CONVERTER FOR HIGH POWER GYROTRONS |
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| Authors: | R Minami A Kasugai K Takahashi N Kobayashi Y Mitsunaka and K Sakamoto |
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| Institution: | (1) Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Ibaraki, Japan;(2) Electron Tube Engineering Department, Toshiba Electron Tubes & Devices Co., LTD, Tochigi, Japan |
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| Abstract: | A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A
helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have
been optimized for the TE31.8 mode at 170 GHz and TE22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking
the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing
in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design.
High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the
thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of
high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons. |
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| Keywords: | mode converter gyrotron high order mode |
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