Kinetic theory of geodesic acoustic modes in toroidal plasmas: a brief review

Abstract

Geodesic acoustic modes (GAM) are oscillating zonal structures unique to toroidal plasmas, and have been extensively studied in the past decades due to their potential capabilities of regulating microscopic turbulences and associated anomalous transport. This article reviews linear and nonlinear theories of GAM; with emphases on kinetic treatment, system nonuniformity and realistic magnetic geometry, in order to reflect the realistic experimental conditions. Specifically, in the linear physics, the resonant wave-particle interactions are discussed, with the application to resonant excitation by energetic particles (EPs). The theory of EP-induced GAM (EGAM) is applied to realistic devices for the interpretation of experimental observations, and global effects due to coupling to GAM continuum are also discussed. Meanwhile, in the nonlinear physics, the spontaneous GAM excitation by microscale turbulences is reviewed, including the effects of various system nonuniformities. A unified theoretical framework of GAM/EGAM is then constructed based on our present understandings. The first-principle-based GAM/EGAM theories reviewed here, thus, provide the tools needed for the understanding and interpretation of experimental/numerical results.

Transport Barrier Triggered by Resonant Three-Wave Processes Between Trapped-Particle-Modes and Zonal Flow

“…Possible scenarii of three-wave processes concerning both CTEM and ZF have been discussed in the review of Qiu, Chen and Zonca in [45]. It is the combined action of polarisation injection and resonant amplification of the LFZF will determine the formation of TB.…”

Linear properties of global energetic particle induced geodesic acoustic mode with bump-on-tail distribution in tokamak plasmas

“…Since then EGAM has been observed in other tokamaks [7][8][9] as well as in the Large Helical Device (LHD) [10][11]. Extensive theoretical and numerical work has been done on the linear physics of EGAM in the past decade [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The research on EGAM has been reviewed recently in several papers [26][27][28].…”

Radial properties of the geodesic acoustic mode

“…The radial propagation of the GAM has been considered in several works. [20][21][22] Accordingly, we consider the effect of n 0 for T i = 6keV, T e = 4keV, R 0 /L T i = 2.4 and R 0 /L n = R 0 /L Te = 6. From the four lines marking the peaks of the mode in Fig.…”