title: Detection of a new parametric decay instability branch in TST-2 during high harmonic fast wave heating.
abstract: Parametric decay instability (PDI) is often observed in the TST-2 spherical tokamak during high harmonic fast wave heating by rf pickup probes. The frequency spectrum exhibits lower and upper sideband peaks in addition to the pump wave at f(0)=21 MHz. Two types of PDI are observed. One is the well-known decay into the ion-cyclotron quasimode (nf(ci)) and the ion Bernstein wave (f(0)-nf(ci)). The other is a newly found decay with the sideband frequency between f(0) and f(0)-f(ci). The frequency difference between this sideband and the pump increases in proportion to B(t). Moreover, high-speed visible light measuring systems with photomultiplier tubes or hybrid photodetectors viewing the plasma core detected oscillation of light emission at around f(0).
authors.affiliation: The University of Tokyo, Kashiwa 277-8561, Japan. adachi@fusion.k.u-tokyo.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Adachi
authors.forename: A
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authors.lastname: Ejiri
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authors.initials: Y
authors.lastname: Takase
authors.forename: O
authors.initials: O
authors.lastname: Watanabe
authors.forename: T
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authors.lastname: Oosako
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authors.lastname: Tojo
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authors.initials: S
authors.lastname: Kainaga
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authors.lastname: Masuda
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authors.lastname: Sasaki
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authors.initials: J
authors.lastname: Sugiyama
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authors.initials: T
authors.lastname: Yamaguchi