04aE60P
GAMMA10セントラル部における高周波波動の空間構造および非線形結合現象
Spatial structure and non-linear coupling phenomenon of high-frequency waves
in the GAMMA10 central cell
池添竜也，岡田拓也，市村 真，平田真史，横山拓郎，飯村拓真，齋藤裕希
岩本嘉章，隅田脩平，渡邊和征，吉川正志，小波蔵純子，嶋頼子
Ryuya Ikezoe, Takuya Okada, Makoto Ichimura, Mafumi Hirata, Takuro Yokoyama et al.
筑波大学プラズマ研究センター
Plasma Research Center, University of Tsukuba
In the GAMMA10 tandem mirror, owing to mirror confinement and effective beach heating byICRF waves, strong anisotropy of ion temperature of greater than 10 is attained. Such a strong
anisotropy destabilizes Alfvén wave in the frequency range below the ion cyclotron frequency andis called Alfvén-ion-cyclotron (AIC) wave1,2. In the GAMMA10 central cell, main confinement
region, the AIC waves are spontaneously excited in the frequency range of 5.6 – 6.0 MHz. They areemerged on that frequency range as discrete sharp peaks, contrary to the geomagnetism where
single broad peak is observed. Since the wavelength of the AIC wave in GAMMA10 is in the sameorder as the size of the confinement region, some boundary condition should be associated with thisdifference.
To clarify the relationship between the discrete peaks of the AIC waves and the boundary
condition in the laboratory anisotropic plasma, we have promoted the measurement of the spatial
structure on high-beta GAMMA10 plasma by using a two-channel reflectometer3. Density
fluctuations at various radial positions and axially separated two positions showed that the power
distribution among the AIC waves changed much both in radial and axial directions especially in theearlier period just after the excitation. Furthermore, transformation of the AIC waves frompropagating to standing waves in the earlier period was also indicated4.
Density fluctuation measured by a reflectometer shows fruitful wave-wave coupling
phenomena. The excited AIC waves interact with each other and with other ICRF waves; several
ICRF waves are externally applied for ion heating. As a result, nonlinearity forms many Alfvén
waves which satisfy three-wave coupling condition. Especially low-frequency waves near 100 kHz,
which is excited by wave-wave coupling between the AIC waves, are important for the axial
confinement of mirror field. Energetic ions are found to be axially transported by interacting withthese low-frequency waves5. As another important feature of the wave-wave coupling, we areconsidering the contribution to the saturation of the stored energy in the GAMMA10 central cell;
the power of heating ICRF waves may be pumped to the AIC waves and the Alfvén waves having
the difference frequency. In the presentation, we will report the spatial structure of the AIC waves
measured by a two-channel reflectometer and also the nonlinear wave-wave coupling phenomenaobserved in the inner region of the GAMMA10 central cell.
This work is partly supported by a Grant-in-Aid for Scientific Research from JSPS, Japan (No.
25400531) and by the bidirectional collaborative research programme of the National Institute forFusion Science, Japan (NIFS12KUGM067)

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