(TH/P2-5) Eigenmode Analysis of Geodesic Acoustic Mode and Zonal Flow

Zhe Gao1), K. Itoh2), H. Sanuki2), J. Q. Dong3)
1) Department of Engineering Physics, Tsinghua University, Beijing, China
2) National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
3) Southwestern Institute of Physics, Chengdu 610041, China

Abstract.  We employ a linear gyrokinetic model in collisionless toroidal plasmas with an electrostatic potential nearly constant around a magnetic surface, and then the plasma response is analytically solved. Besides the trivial zero frequency solution and the standard GAM solution, a branch of low frequency mode and an infinite series of ISW-like modes are found. The ISW-like modes are strongly damped. For a low electron/ion temperature ratio, τ, the low frequency eigenmode has a rigid zero frequency in the low q region but oscillates with a finite frequency in the high q region. The critical value of q increases and the finite frequency decreases with an increasing τ. Until τ is larger than 0.55, the mode has a rigid zero frequency for all q. This low frequency eigenmode relaxes on time scaling with the order of transit frequency.

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