Observation of beat oscillation generation by coupled waves associated with parametric decay during radio frequency wave heating of a spherical tokamak plasma

Yoshihiko Nagashima, Takuya Oosako, Yuichi Takase, Akira Ejiri, Osamu Watanabe, Hiroaki Kobayashi, Yuuki Adachi, Hiroshi Tojo, Takashi Yamaguchi, Hiroki Kurashina, Kotaro Yamada, Byung Il An, Hiroshi Kasahara, Fujio Shimpo, Ryuhei Kumazawa, Hiroyuki Hayashi, Haduki Matsuzawa, Junichi Hiratsuka, Kentaro Hanashima, Hidetoshi KakudaTakuya Sakamoto, Takuma Wakatsuki

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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.

Original languageEnglish
Article number245002
JournalPhysical Review Letters
Issue number24
Publication statusPublished - Jun 16 2010
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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