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