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High Efficiency Mode Converter for Low-Frequency Gyrotron

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Abstract

A high efficiency quasi-optical (QO) mode converter for high-power, low-frequency gyrotron have been designed and tested. For low-frequency gyrotrons, the scales of the mode converter are comparatively small on the wavelength scale, thus causing significant diffraction losses. Over-1 MW power gyrotron with TE8,3 cavity at 28 GHz have been developed, which has a high efficiency mode converter designed by the use of numerical methods for launcher optimization. This calculation is sufficiently optimized to maximize the fractional Gaussian content of the far field. The total transmission efficiency from the mode converter to output window is 94.7%. For the experimental result of first tube, the output power of more than 1 MW has been obtained with about 40% efficiency and output burn pattern agrees fairly with the calculated profiles, which imply the design appropriateness. Besides, the frequency dependence for diffraction loss is discussed, and these results give the guiding design principle of the mode converter for high-power, low-frequency and long-pulse gyrotrons.

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Acknowledgments

The authors would like to thank Profs. S. Kubo, T. Shimozuma and T. Mutoh of NIFS for their collaboration. We also would like to thank Mr. Endo and the members of the GAMMA 10 group for valuable discussion and support of the experiments. This work is partially supported by NIFS Collaborative program (NIFS04KUGM009, NIFS05KOAR006 and NIFS07KUGM009).

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Authors and Affiliations

  1. Plasma Research Center (PRC), University of Tsukuba, Ibaraki, Japan

    Ryutaro Minami, Tsuyoshi Kariya & Tsuyoshi Imai

  2. Electron Tube Engineering Department, Toshiba Electron Tubes & Devices Co., LTD (TETD), Tochigi, Japan

    Yoshika Mitsunaka

  3. Plasma Heating Technology Group, Japan Atomic Energy Agency (JAEA), Ibaraki, Japan

    Keishi Sakamoto

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  1. Ryutaro Minami
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  2. Tsuyoshi Kariya
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  3. Tsuyoshi Imai
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  4. Yoshika Mitsunaka
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  5. Keishi Sakamoto
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Correspondence to Ryutaro Minami.

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Minami, R., Kariya, T., Imai, T. et al. High Efficiency Mode Converter for Low-Frequency Gyrotron. J Infrared Milli Terahz Waves 32, 311–319 (2011). https://doi.org/10.1007/s10762-010-9719-8

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  • DOI: https://doi.org/10.1007/s10762-010-9719-8

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