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

Tomonari Nakayama; Motoki Nakata; Mitsuru Honda; Emi Narita; Masanori Nunami; Seikichi Matsuoka

doi:10.1038/s41598-023-29168-w

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

Sci Rep. 2023 Mar 16;13(1):2319. doi: 10.1038/s41598-023-29168-w.

Authors

Tomonari Nakayama¹, Motoki Nakata^{2

3

4}, Mitsuru Honda⁵, Emi Narita⁶, Masanori Nunami^{3

7}, Seikichi Matsuoka^{2

3}

Affiliations

¹ The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu, 509-5292, Japan. nakayama.tomonari@nifs.ac.jp.
² The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu, 509-5292, Japan.
³ National Institute for Fusion Science, Toki, Gifu, 509-5292, Japan.
⁴ PRESTO, Japan Science and Technology Agency, 418, Honcho, Kawaguchishi, Saitama, 332-0012, Japan.
⁵ Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto, 615-8530, Japan.
⁶ National Institutes for Quantum Science and Technology, Naka, Ibaraki, 311-0193, Japan.
⁷ Nagoya University, Graduate School of Science, Nagoya, Aichi, 464-8603, Japan.

Abstract

A 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 [Formula: see text], and the zonal-flow intensity [Formula: see text] is determined by means of mathematical optimization methods. Then, an extended modeling for [Formula: see text] and [Formula: see text] 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 [Formula: see text] indicates improvement by a factor of about 1/4 in comparison to that in the previous works.