Observation of Beat Oscillation Generation by Coupled Waves Associated with Parametric Decay during Radio Frequency Wave Heating of a Spherical Tokamak Plasma

Journal Article · Fri Jun 18 00:00:00 EDT 2010 · Physical Review Letters

DOI:https://doi.org/10.1103/PHYSREVLETT.104.245002· OSTI ID:21410423

Nagashima, Yoshihiko; Oosako, Takuya; Takase, Yuichi; Ejiri, Akira; Watanabe, Osamu; Kobayashi, Hiroaki; Adachi, Yuuki; Yamaguchi, Takashi; Kurashina, Hiroki; Yamada, Kotaro; Hayashi, Hiroyuki; Matsuzawa, Haduki; Hanashima, Kentaro; Sakamoto, Takuya ^[1]; Tojo, Hiroshi ^[2]; An, Byung Il; Hiratsuka, Junichi; Kakuda, Hidetoshi; Wakatsuki, Takuma ^[3]; Kasahara, Hiroshi ^[4]

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1. Graduate School of Frontier Sciences, University of Tokyo, Kashiwa-shi, Chiba 277-8561 (Japan)
2. Naka Fusion Institute, Japan Atomic Energy Agency, Naka-shi, Ibaraki 311-0193 (Japan)
3. Graduate School of Science, University of Tokyo, Kashiwa-shi, Chiba 277-8561 (Japan)
4. National Institute for Fusion Science, Toki-shi, Gifu 509-5292 (Japan)

We present an observation of beat oscillation generation by coupled modes associated with parametric decay instability (PDI) during radio frequency (rf) wave heating experiments on the Tokyo Spherical Tokamak-2. Nearly identical PDI spectra, which are characterized by the coexistence of the rf pump wave, the lower-sideband wave, and the low-frequency oscillation in the ion-cyclotron range of frequency, are observed at various locations in the edge plasma. A bispectral power analysis was used to experimentally discriminate beat oscillation from the resonant mode for the first time. The pump and lower-sideband waves have resonant mode components, while the low-frequency oscillation is exclusively excited by nonlinear coupling of the pump and lower-sideband waves. Newly discovered nonlocal transport channels in spectral space and in real space via PDI are described.

• OSTI ID: 21410423
• Journal Information: Physical Review Letters, Vol. 104, Issue 24; Other Information: DOI: 10.1103/PhysRevLett.104.245002; (c) 2010 The American Physical Society; ISSN 0031-9007
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
COUPLING
CYCLOTRONS
DECAY
DECAY INSTABILITY
NONLINEAR PROBLEMS
PLASMA
RADIOWAVE RADIATION
RF SYSTEMS
SPECTRA
SPHERICAL CONFIGURATION
TOKAMAK DEVICES
ACCELERATORS
CLOSED PLASMA DEVICES
CONFIGURATION
CYCLIC ACCELERATORS
ELECTROMAGNETIC RADIATION
INSTABILITY
PLASMA INSTABILITY
RADIATIONS
THERMONUCLEAR DEVICES