Reduced models of turbulent transport in helical plasmas including effects of zonal flows and trapped electrons

Abstract

Using transport models, the impacts of trapped electrons on zonal flows and turbulence in helical field configurations are studied. The effect of the trapped electrons on the characteristic quantities of the linear response for zonal flows is investigated for two different field configurations in the Large Helical Device. The turbulent potential fluctuation, zonal flow potential fluctuation and ion energy transport are quickly predicted by the reduced models for which the linear and nonlinear simulation results are used to determine dimensionless parameters related to turbulent saturation levels and typical zonal flow wavenumbers. The effects of zonal flows on the turbulent transport for the case of the kinetic electron response are much smaller than or comparable to those in an adiabatic electron condition for the two different field configurations. It is clarified that the effect of zonal flows on the turbulent transport due to the trapped electrons changes, depending on the field configurations.

Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators

“…[8][9][10][11] Linear zonal flow damping is often examined as a proxy for the full zonal flow evolution 12 and is used in models to predict turbulent transport. 13,14 The Rosenbluth-Hinton model 15 provides a zonal flow residual that describes the undamped part of the poloidal flow in a large-aspect-ratio tokamak. This undamped flow acts to saturate drift wave turbulence, and the residual is used as a measure of the amplitude that zonal flows achieve in nonlinear simulations.…”

Nonlinear functional relation covering near- and far-marginal stability in ion temperature gradient driven turbulence

“…The NFR itself can not reduce the computational costs in the transport simulations, because T and Z are obtained from nonlinear simulation. There are several works on constructing further simplified transport modeling by utilizing the NFR [18][19][20][21][22]. It also can be applicable to construct global flux driven turbulent simulations such as GT5D [27], GKNET [41], and GYSELA [42].…”

“…Moreover, a combined modeling based on the linear and nonlinear gyrokinetic simulations has also been explored, where the impacts of turbulence nonlinearity and zonal flow generation on the ion temperature gradient (ITG) driven turbulent thermal transport for ions have been taken into account [18]. An extension to the electron-thermal and particle transport has been applied in the similar manner [19][20][21][22].…”

“…Encompassing such strong zonal flow effects is necessary to accurately predict the dynamical evolutions of the kinetic profiles and the magnetic equilibria. Once the systematic methodology to proposed an accurate NFR is established, various simplified transport models can be induced by combining the conventional modelings [18][19][20][21][22] with linear calculations as in [18]. Also, the phenomenological arguments in the present NFR approach enable us to extract the physical interpretations and useful suggestions to improve the accuracy.…”

Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators

“…Strong zonal flows have been found to be important in configurations such as tokamaks [4] or the reversed-field pinch [5][6][7], and they can affect turbulence saturation in stellarators as well. [8][9][10][11] Linear zonal flow damping is often examined as a proxy for the full zonal flow evolution [12] and is used in models to predict turbulent transport [13,14]. The Rosenbluth-Hinton model [15] provides a zonal flow residual that describes the undamped part of the poloidal flow in a large-aspect-ratio tokamak.…”