Abstract
Virtually, all existing theoretical works on turbulent poloidal momentum transport are based on quasilinear theory. Nonlinear poloidal momentum flux— is universally neglected. However, in the strong turbulence regime where relative fluctuation amplitude is no longer small, quasilinear theory is invalid. This is true at the all-important plasma edge. In this work, nonlinear poloidal momentum flux in strong electrostatic turbulence is calculated using the Hasegawa–Mima equation, and is compared with quasilinear poloidal Reynolds stress. A novel property is that symmetry breaking in fluctuation spectrum is not necessary for a nonlinear poloidal momentum flux. This is fundamentally different from the quasilinear Reynold stress. Furthermore, the comparison implies that the poloidal rotation drive from the radial gradient of nonlinear momentum flux is comparable to that from the quasilinear Reynolds force. Nonlinear poloidal momentum transport in strong electrostatic turbulence is thus not negligible for poloidal rotation drive, and so may be significant to transport barrier formation.
Highlights
It is well known that poloidal rotation plays a crucial role in suppressing microturbulence through its impact on E × B shear [1, 2]
Since poloidal rotation can be significant for triggering the formation of transport barriers [3,4,5,6] through E × B flow shear and leading to improvement of confinement and fusion performance, there have been intensive theoretical and experimental investigations into understanding of poloidal momentum transport and poloidal roation generation [7, 8] .Most theoretical works have been developed based on neoclassical calculations for both core and edge plasmas and for different collisionality [9,10,11,12]
We find that symmetry breaking in fluctuation spectrum is not required for the nonlinear poloidal momentum flux, which is fundamentally different from the Reynolds stress
Summary
It is well known that poloidal rotation plays a crucial role in suppressing microturbulence through its impact on E × B shear [1, 2]. Since poloidal rotation can be significant for triggering the formation of transport barriers [3,4,5,6] through E × B flow shear and leading to improvement of confinement and fusion performance, there have been intensive theoretical and experimental investigations into understanding of poloidal momentum transport and poloidal roation generation [7, 8] .Most theoretical works have been developed based on neoclassical calculations for both core and edge plasmas and for different collisionality [9,10,11,12] In some experiments, such as MAST[13] and NSTX[14], the measured poloidal rotation is consistent with neoclassical predictions. We calculate the nonlinear poloidal momentum flux using the Hasegawa-Mima (H-M) equation [32], which is a popular drift wave model and can be reduced from Hasegawa-Wakatani model[33] for the adiabatic electron limit We compare it with the quasilinear Reynolds stress presented in [22].
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