Detection of a new parametric decay instability branch in TST-2 during high harmonic fast wave heating.
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).
Adachi
Y
Y
The University of Tokyo, Kashiwa 277-8561, Japan. adachi@fusion.k.u-tokyo.ac.jp
Ejiri
A
A
Takase
Y
Y
Watanabe
O
O
Oosako
T
T
Tojo
H
H
Kainaga
S
S
Masuda
T
T
Sasaki
M
M
Sugiyama
J
J
Yamaguchi
T
T