Axial Structures of the Alfven Ion Cyclotron Mode in the GAMMA10 Tandem Mirror.

概要

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Axial structures of the Alfvén ion cyclotron (AIC) mode have been investigated in the GAMMA10 tandem mirror. The AIC mode is a microinstability driven by an anisotropy in the velocity space, and is excited as an axial eigenmode in the GAMMA10. There are several discrete peaks in the frequency range of ω /Ω ci~ 0.8-0.9, where Ω ci is the ion cyclotron frequency at the midplane of the central cell. A driving term of the AIC mode is theoretically given by β ⊥(T⊥/T//)2. Here, β ⊥ is a perpendicular beta value and T⊥/T// is a temperature anisotropy (an ion temperature ratio between perpendicular and parallel to the magnetic field line). In GAMMA10, the AIC mode is observed in the range of β ⊥(T⊥/T//)2≥ 0.3 (which is much smaller than the theoretical prediction of β ⊥(T⊥/T//)2≥ 3.52). This is thought to be related to the wave structure in the axial direction. The frequency ω and axial wave number k// of each mode changed with β ⊥ and T⊥/T//. As β ⊥ and T⊥/T// increased, the AIC frequency range became wide and the AIC wave changed from a propagating wave to a standing wave.
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