Suppression of spurious mode oscillation in mega-watt 77-GHz gyrotron as a high quality probe beam source for the collective Thomson scattering in LHD

Journal Article · Mon Oct 15 04:00:00 EDT 2012 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4740257· OSTI ID:22093866

Ogasawara, S. ^[1]; Kubo, S. ^[1]; Nishiura, M.; Tanaka, K.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Takahashi, H.; Ito, S.; Takita, Y.; Kobayashi, S.; Mizuno, Y.; Okada, K. ^[2]; Tatematsu, Y.; Saito, T. ^[3]; Minami, R.; Kariya, T.; Imai, T. ^[4]

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1. Department of Energy Engineering and Science, Nagoya University, Nagoya 464-8463 (Japan)
2. National Institute for Fusion Science, 322-6 Oroshi-cho, Toki-shi 509-5292 (Japan)
3. Research Center for Development of Far-Infrared Region, University of Fukui, Fukui 910-8507 (Japan)
4. Plasma Research Center, University of Tsukuba, Tsukuba 305-8577 (Japan)

Collective Thomson scattering (CTS) diagnostic requires a strong probing beam to diagnose a bulk and fast ion distribution function in fusion plasmas. A mega-watt gyrotron for electron cyclotron resonance heating is used as a probing beam in the large helical device. Spurious mode oscillations are often observed during the turning on/off phase of the modulation. The frequency spectra of the 77-GHz gyrotron output power have been measured, and then one of the spurious modes, which interferes with the CTS receiver system, is identified as the TE{sub 17,6} mode at the frequency of 74.7 GHz. The mode competition calculation indicates that the increase of the magnetic field strength at the gyrotron resonator can avoid such a spurious mode and excite only the main TE{sub 18,6} mode. The spurious radiation at the 74.7 GHz is experimentally demonstrated to be suppressed in the stronger magnetic field than that optimized for the high-power operation.

• OSTI ID: 22093866
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 83; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
DISTRIBUTION FUNCTIONS
ECR HEATING
INHIBITION
INSTABILITY
IONS
LHD DEVICE
MAGNETIC FIELDS
MICROWAVE AMPLIFIERS
MODULATION
OSCILLATION MODES
PLASMA
PLASMA DIAGNOSTICS
PLASMA WAVES
RESONATORS
SPECTRA
THOMSON SCATTERING