In some lecture report[1] they say Zonal flow stands for the mode with toroidal/poloidal mode number n=m=0 mode in plasma physics. So the n=0, m!=0 Geodesic Acoustic Mode (GAM) is not Zonal flow. But in other paper[2][3], they say GAM is also a kind of Zonal flow. So who is right and who is wrong? Exactly what is zonal flow in plasma physics?
[1] https://fire.pppl.gov/iaea04_diamond.pdf
[2] L.W. Yan et al 2007 Nucl. Fusion 47 1673 Three-dimensional features of GAM zonal flows in the HL-2A tokamak
[3] L. Lachhvani, J. Ghosh, P. K. Chattopadhyay, N. Chakrabarti, and R. Pal, “Observation of geodesic acoustic mode in SINP-tokamak and its behaviour with varying edge safety factor,” Phys. Plasmas, vol. 24, no. 11, 2017.
Dear Nan Chu,
In my view, they are nor right or wrong, it is a subject of definition. It looks like you have a tokamak in mind. Toroidal and poloidal rotations in tokamaks are analogs of the zonal flows in the atmosphere, while oscillations of plasma pressure are analogs of GAM.
In reference with the ITER plasmas, the GAM oscillation is a perturbation ---- which is constant on the magnetic surface ---- but, oscillates in the radial direction. This GAM is a stable mode, which can be excited by the background drift wave turbulence.
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