[Table of Contents]

Plasma and Fusion Research

Volume 7, 2405061 (2012)

Regular Articles

Identification of Spurious Modes of High-Power 77-GHz Gyrotron for Collective Thomson Scattering in LHD
Shinya OGASAWARA1), Shin KUBO1,2), Masaki NISHIURA2), Yoshinori TATEMATSU3), Teruo SAITO3), Kenji TANAKA2), Takashi SHIMOZUMA2), Yasuo YOSHIMURA2), Hiroe IGAMI2), Hiromi TAKAHASHI2), Satoshi ITO2), Yasuyuki TAKITA2), Sakuji KOBAYASHI2), Yoshinori MIZUNO2), Kohta OKADA2), Ryutaro MINAMI4), Tsuyoshi KARIYA4) and Tsuyoshi IMAI4)
Department of Energy Engineering and Technology, Nagoya University, Nagoya 464-8463, Japan
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
Research Center for Development of FIR, University of Fukui, Fukui 910-8507, Japan
Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
(Received 9 December 2011 / Accepted 22 March 2012 / Published 07 June 2012)


Frequency measurements at 74-80 GHz were conducted for the identification and suppression of spurious modes from the 77-GHz gyrotron, which was originally introduced as a power source for electron cyclotron resonance heating and is now also used as a probe beam for the collective Thomson scattering (CTS) diagnostic. The spurious modes are excited as the gyrotron output power is turned on and off by controlling the anode voltage. These modes are harmful for the CTS diagnostic, even though their power is less than approximately 50 dB below than that of the main mode. The measured frequency of one of the spurious modes is approximately 74.7 GHz. The cavity structure, starting current calculation, and mode competition calculation suggest that the spurious mode is the TE17,6 mode. The result is important for optimizing the gyrotron operation as a CTS probe beam and suppressing or minimizing the spurious mode excitation.


collective Thomson scattering, gyrotron, ECRH, LHD, ECE, transverse electric (TE) mode

DOI: 10.1585/pfr.7.2405061


  • [1] H. Bindslev, S.K. Nielsen et al., Phys. Rev. Lett. 97, 205005 (2006).
  • [2] M. Nishiura, S. Kubo et al., Journal of Physics: Conference Series 227, 012014 (2010).
  • [3] S. Kubo, M. Nishiura et al., Rev. Sci. Instrum. 81, 10D535 (2010).
  • [4] M. Nishiura, K. Tanaka et al., Rev. Sci. Instrum. 79, 10E731 (2008).
  • [5] S. Kubo, K. Tanaka et al., J. Plasma. Fusion. Res. 87, 350 (2011) (in Japanese).
  • [6] Y. Tatematsu and T. Saito, J. Plasma. Fusion. Res. 84, 855 (2008) (in Japanese).
  • [7] T. Kariya, R. Minami et al., Trans. of Fusion Science and Technology 55, No.2T, 91 (2009).

This paper may be cited as follows:

Shinya OGASAWARA, Shin KUBO, Masaki NISHIURA, Yoshinori TATEMATSU, Teruo SAITO, Kenji TANAKA, Takashi SHIMOZUMA, Yasuo YOSHIMURA, Hiroe IGAMI, Hiromi TAKAHASHI, Satoshi ITO, Yasuyuki TAKITA, Sakuji KOBAYASHI, Yoshinori MIZUNO, Kohta OKADA, Ryutaro MINAMI, Tsuyoshi KARIYA and Tsuyoshi IMAI, Plasma Fusion Res. 7, 2405061 (2012).