title: Observation of beat oscillation generation by coupled waves associated with parametric decay during radio frequency wave heating of a spherical tokamak plasma.
abstract: 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.
authors.affiliation: Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-shi, Chiba 277-8561, Japan. nagashima@k.u-tokyo.ac.jp
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Nagashima
authors.forename: Takuya
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authors.lastname: Oosako
authors.forename: Yuichi
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authors.lastname: Takase
authors.forename: Akira
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authors.lastname: Ejiri
authors.forename: Osamu
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authors.lastname: Watanabe
authors.forename: Hiroaki
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authors.lastname: Kobayashi
authors.forename: Yuuki
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authors.lastname: Adachi
authors.forename: Hiroshi
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authors.lastname: Tojo
authors.forename: Takashi
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authors.lastname: Yamaguchi
authors.forename: Hiroki
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authors.lastname: Kurashina
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authors.lastname: Yamada
authors.forename: Byung Il
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authors.forename: Hiroshi
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authors.lastname: Kasahara
authors.forename: Fujio
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authors.lastname: Shimpo
authors.forename: Ryuhei
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authors.lastname: Kumazawa
authors.forename: Hiroyuki
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authors.lastname: Hayashi
authors.forename: Haduki
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authors.lastname: Matsuzawa
authors.forename: Junichi
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authors.lastname: Hiratsuka
authors.forename: Kentaro
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authors.lastname: Hanashima
authors.forename: Hidetoshi
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authors.lastname: Kakuda
authors.forename: Takuya
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authors.lastname: Sakamoto
authors.forename: Takuma
authors.initials: T
authors.lastname: Wakatsuki