A simplified model to estimate nonlinear turbulent transport by linear dynamics in plasma turbulence

Abstract

AbstractA simplified model to estimate nonlinear turbulent transport only by linear calculations is proposed, where the turbulent heat diffusivity in tokamak ion temperature gradient(ITG) driven turbulence is reproduced for a wide parameter range including near- and far-marginal ITG stability. The optimal nonlinear functional relation(NFR) between the turbulent diffusivity, the turbulence intensity $$\mathcal{T}$$ T , and the zonal-flow intensity $$\mathcal{Z}$$ Z is determined by means of mathematical optimization methods. Then, an extended modeling for $$\mathcal{T}$$ T and $$\mathcal{Z}$$ Z to incorporate the turbulence suppression effects and the temperature gradient dependence is carried out. The simplified transport model is expressed as a modified nonlinear function composed of the linear growth rate and the linear zonal-flow decay time. Good accuracy and wide applicability of the model are demonstrated, where the regression error of $$\sigma _{\textrm{model}} = 0.157$$ σ model = 0.157 indicates improvement by a factor of about 1/4 in comparison to that in the previous works.