Turbulence suppression at extreme plasma densities on DIII-D and EAST

Recent high-poloidal-beta (high-βP) experiments on DIII-D and EAST have made coordinated breakthroughs for high confinement quality at high density near the Greenwald limit. Density gradient amplification of turbulence suppression at high βP can explain both of these achievements. Experiments on DIII-D have achieved Greenwald fraction (fGr = line-averaged density/Greenwald density) above 1 simultaneously with normalized energy confinement (H98y2) around 1.5, as required in fusion reactor designs but never before verified in tokamak experiments with the divertor configuration. A synergy between increased H98y2 and fGr is observed with strong gas puffing, due to the build-up of an internal transport barrier at large radius in the temperature and density channels. Transport simulations reveal that the favorable trend of reduced turbulent energy transport at higher density is only expected when increasing the density gradient at high local safety factor and high β, thus at high βP to ensure strong α-stabilization. These conditions are crucial to many conceptual designs for steady-state reactors. New experiments on EAST have nearly doubled the ion temperature at fGr ∼ 0.9, consistent with predict-first modeling results based on the same physics revealed from the DIII-D analysis. All previous EAST long-pulse H-modes have Ti ≪ Te near plasma axis. Transport modeling indicates that the profiles are limited by ion-temperature-gradient modes at mid-radius. The modeling also suggested potential solutions, including reducing magnetic shear, enhancing density gradients, and higher impurity concentration. Following this guidance, EAST experiments directly show a strong enhancement of Ti achieved with a combination of a second plasma current ramp-up, a density gradient increase, and a Zeff perturbation by a short pulse (100 ms) of impurity injection, as predicted by the earlier modeling.

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Publication Details

Journal
Physics of Plasmas
Published
2025-02-01
DOI
https://doi.org/10.1063/5.0235599
Citations
3
Primary Topic
Magnetic confinement fusion research
Type
article
Field-Weighted Citation Impact
5.61

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article

Turbulence suppression at extreme plasma densities on DIII-D and EAST

A. Marinoni, J.P. Qian, S. M. Mahajan, B.S. Victor et al.
3 citations
Physics of Plasmas
Magnetic confinement fusion research
5.61
article

Turbulence suppression at extreme plasma densities on DIII-D and EAST

A. Marinoni, J.P. Qian, S. M. Mahajan, B.S. Victor, D. Eldon, S. Ding, J.M. Hanson, I.S. Carvalho, Yuxin Sun, Zuhao Wang, Xiaojing Gong, T. Odstrčil, Kedong Li, Zeyu Li, Qiming Hu, G. M. Wallace, Huiqian Wang, David B. Weisberg, A. M. Garofalo, J. McClenaghan, M. Kotschenreuther, X. Jian, W. Choi, P. T. Bonoli, J. Huang, Z. Yan, D. R. Hatch, A.W. Hyatt, C. T. Holcomb, S. G. Baek, T.H. Osborne, Liang Wang
article en
3 citations

Abstract

Recent high-poloidal-beta (high-βP) experiments on DIII-D and EAST have made coordinated breakthroughs for high confinement quality at high density near the Greenwald limit. Density gradient amplification of turbulence suppression at high βP can explain both of these achievements. Experiments on DIII-D have achieved Greenwald fraction (fGr = line-averaged density/Greenwald density) above 1 simultaneously with normalized energy confinement (H98y2) around 1.5, as required in fusion reactor designs but never before verified in tokamak experiments with the divertor configuration. A synergy between increased H98y2 and fGr is observed with strong gas puffing, due to the build-up of an internal transport barrier at large radius in the temperature and density channels. Transport simulations reveal that the favorable trend of reduced turbulent energy transport at higher density is only expected when increasing the density gradient at high local safety factor and high β, thus at high βP to ensure strong α-stabilization. These conditions are crucial to many conceptual designs for steady-state reactors. New experiments on EAST have nearly doubled the ion temperature at fGr ∼ 0.9, consistent with predict-first modeling results based on the same physics revealed from the DIII-D analysis. All previous EAST long-pulse H-modes have Ti ≪ Te near plasma axis. Transport modeling indicates that the profiles are limited by ion-temperature-gradient modes at mid-radius. The modeling also suggested potential solutions, including reducing magnetic shear, enhancing density gradients, and higher impurity concentration. Following this guidance, EAST experiments directly show a strong enhancement of Ti achieved with a combination of a second plasma current ramp-up, a density gradient increase, and a Zeff perturbation by a short pulse (100 ms) of impurity injection, as predicted by the earlier modeling.

Physics of PlasmasVol. 32(2)
University of Science and Technology of China (CN), Lawrence Livermore National Laboratory (US), University of Wisconsin–Madison (US), Chinese Academy of Sciences (CN), Princeton University (US), Princeton Plasma Physics Laboratory (US), University of California San Diego (US), Bellevue Hospital Center (US), Institute of Plasma Physics (CN), Plasma Technology (United States) (US), Fusion Academy (US), General Atomics (United States) (US), Massachusetts Institute of Technology (US), Columbia University (US)
Office of Science
Affordable and clean energy
Openalex Percentile: Top 6%
Magnetic confinement fusion research
5.61
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