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Turbulence Trapping in Radial Electric Field Well at H-Mode Transport Barrier in JFT-2M Tokamak

Tatsuya KOBAYASHI^1,2,3), Makoto SASAKI⁴⁾

1)

National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan

2)

The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan

3)

Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan

4)

College of Industrial Technology, Nihon University, Narashino 275-8575, Japan

(Received 13 April 2026 / Accepted 14 April 2026 / Published 3 July 2026)

Abstract

In this paper, an experimental consistency check for a theory describing the interplay between micro-scale turbulence and meso- and macro-scale flows is presented. The experimental data obtained in the JFT-2M tokamak are used for the consistency check. After L-H transition, a solitary radial electric field well, driving an E × B flow structure in the electron diamagnetic direction, forms. Turbulence is regulated in the flow shear regions, while it nearly remains essentially unchanged at the peak of the flow structure where the shear is zero. In a theory, this type of turbulence redistribution, called hill-trapping, is predicted to occur when the adiabatic parameter α is larger than unity. In the experiment, α ∼ 40 ≫ 1 is given, supporting the theory. An eigenmode model analysis for the turbulence system is performed for the experimental parameters, and the occurrence of the hill-trapping is found.

Copyright (c) 2026 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

turbulence, radial electric field, H-mode, transport barrier, Hasegawa-Wakatani model, turbulence trapping

DOI: 10.1585/pfr.21.1402035

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