Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport

Hegna, Chris C.; Terry, Paul W.; Faber, Ben J.

doi:10.1063/1.5018198

Title: Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport

Journal Article · 01 February 2018 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.5018198 · OSTI ID:1418997

Hegna, Chris C. ^[1]; Terry, Paul W. ^[1]; Faber, Ben J. ^[1]

Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics and Physics

A three-field fluid model that allows for general three-dimensional equilibrium geometry is developed to describe ion temperature gradient turbulent saturation processes in stellarators. The theory relies on the paradigm of nonlinear transfer of energy from unstable to damped modes at comparable wavelength as the dominant saturation mechanism. The unstable-to-damped mode interaction is enabled by a third mode that for dominant energy transfer channels primarily serves as a regulator of the nonlinear energy transfer rate. The identity of the third wave in the interaction defines different scenarios for turbulent saturation with the dominant scenario depending upon the properties of the 3D geometry. The nonlinear energy transfer physics is quantified by the product of a turbulent correlation lifetime and a geometric coupling coefficient. The turbulent correlation time is determined by a three-wave frequency mismatch, which at long wavelength can be calculated from the sum of the linear eigenfrequencies of the three modes. Larger turbulent correlation times denote larger levels of nonlinear energy transfer and hence smaller turbulent transport. The theory provides an analytic prediction for how 3D shaping can be tuned to lower turbulent transport through saturation processes.

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Research Organization:: Univ. of Wisconsin, Madison, WI (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: FG02-99ER54546; FG02-93ER54222; FG02-89ER53291

OSTI ID:: 1418997

Alternate ID(s):: OSTI ID: 1420362

Journal Information:: Physics of Plasmas, Vol. 25, Issue 02; ISSN 1089-7674

Country of Publication:: United States

Language:: English

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Cited by: 27 works

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