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Nonlinear MHD simulation of sawtooth crash and saturated steady-state regimes in EAST electron heating-dominant high βp discharge.

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Title: Nonlinear MHD simulation of sawtooth crash and saturated steady-state regimes in EAST electron heating-dominant high βp discharge.
Authors: Wang, W.1,2 (AUTHOR), Zhou, Y.3 (AUTHOR) yao.zhou@sjtu.edu.cn, Xu, L. Q.1 (AUTHOR) lqxu@ipp.ac.cn, Gong, X. Z.1 (AUTHOR), Qian, J. P.1 (AUTHOR), Zhang, B.1 (AUTHOR), Zhao, H. L.1 (AUTHOR), Li, G. Q.1 (AUTHOR), Lin, Z. C.1,2 (AUTHOR), Wang, S. X.1 (AUTHOR), Li, P.1 (AUTHOR), Liu, W. B.1 (AUTHOR), Hu, Y. C.1,2 (AUTHOR), Wang, Z. H.4 (AUTHOR), Guo, Y. T.1,2 (AUTHOR), Jia, T. Q.1 (AUTHOR), Chao, Y.1 (AUTHOR)
Source: European Physical Journal D (EPJ D). May2026, Vol. 80 Issue 5, p1-18. 18p.
Subjects: Magnetohydrodynamics, Magnetohydrodynamic instabilities, Plasma confinement, Plasma flow, Tokamaks, Electron temperature, Plasma stability
Abstract: This study investigates the relationship between the saturated steady m/n = 1/1 mode (SSM) and sawtooth crash (SC) in the Experimental Advanced Superconducting Tokamak (EAST) device. In a dominantly electron-heated, high- β p discharge, we observe a spontaneous transition from SC to SSM. This transition is accompanied by a sudden change in the current distribution, as indicated by a decrease in self-inductance ( li ). This transition occurs without any changes in external conditions, and notably, results in enhanced confinement. We employed the M3D-C1 code to simulate the SC before and the SSM after this transition. The results indicate that the periodic SC is induced by the periodic growth of the m = 1 internal kink mode for q 0 < 1 . However, when q 0 is slightly below 1 and weakly sheared, a steady quasi-interchange mode forms. The nonlinear flux pumping mechanism, driven by the strong flow field of the quasi-interchange mode, redistributes the core current toward the region near the q = 1 surface. These effects prevent the continuous decrease in q 0 and the occurrence of SC. We observe distinct perturbation characteristics between the internal kink mode and the quasi-interchange mode that reveals different features, which are consistent with the experimental results. Nonlinear resistive MHD simulations with M3D-C1 reproduce the transition from periodic sawtooth crashes (SCs) to a saturated steady mode (SSM) in an EAST electron heating-dominant high-βp discharge. Figure a illustrates the spatiotemporal evolution of the dominant m/n = 1/1 activity: The Poincaré plots show the change of core magnetic topology together with the corresponding 2D structures of the perturbed pressure δ p , toroidal current perturbation δJφ, and plasma flows v φ , v p at representative times. During the crash stage, the core profiles collapse rapidly and the 1/1 structure is accompanied by a strong, localized current sheet signature and a pronounced hot–cold δ p pattern, whereas in the later phase the m = 1 structure persists without repeated large-scale collapses, consistent with a sustained weak-shear, QI-like steady state. Figure b provides complementary temporal signatures: The helical-current components I t and the n = 1 kinetic energy indicate impulsive energy release during the crash, followed by a reduced and slowly varying kinetic energy level as the system relaxes toward a steady regime, consistent with saturation of the n = 1 dynamics and stabilization of the core current redistribution process. [ABSTRACT FROM AUTHOR]
Copyright of European Physical Journal D (EPJ D) is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Nonlinear MHD simulation of sawtooth crash and saturated steady-state regimes in EAST electron heating-dominant high βp discharge.
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  Data: This study investigates the relationship between the saturated steady m/n = 1/1 mode (SSM) and sawtooth crash (SC) in the Experimental Advanced Superconducting Tokamak (EAST) device. In a dominantly electron-heated, high- β p discharge, we observe a spontaneous transition from SC to SSM. This transition is accompanied by a sudden change in the current distribution, as indicated by a decrease in self-inductance ( li ). This transition occurs without any changes in external conditions, and notably, results in enhanced confinement. We employed the M3D-C1 code to simulate the SC before and the SSM after this transition. The results indicate that the periodic SC is induced by the periodic growth of the m = 1 internal kink mode for q 0 &lt; 1 . However, when q 0 is slightly below 1 and weakly sheared, a steady quasi-interchange mode forms. The nonlinear flux pumping mechanism, driven by the strong flow field of the quasi-interchange mode, redistributes the core current toward the region near the q = 1 surface. These effects prevent the continuous decrease in q 0 and the occurrence of SC. We observe distinct perturbation characteristics between the internal kink mode and the quasi-interchange mode that reveals different features, which are consistent with the experimental results. Nonlinear resistive MHD simulations with M3D-C1 reproduce the transition from periodic sawtooth crashes (SCs) to a saturated steady mode (SSM) in an EAST electron heating-dominant high-βp discharge. Figure a illustrates the spatiotemporal evolution of the dominant m/n = 1/1 activity: The Poincar&#233; plots show the change of core magnetic topology together with the corresponding 2D structures of the perturbed pressure δ p , toroidal current perturbation δJφ, and plasma flows v φ , v p at representative times. During the crash stage, the core profiles collapse rapidly and the 1/1 structure is accompanied by a strong, localized current sheet signature and a pronounced hot–cold δ p pattern, whereas in the later phase the m = 1 structure persists without repeated large-scale collapses, consistent with a sustained weak-shear, QI-like steady state. Figure b provides complementary temporal signatures: The helical-current components I t and the n = 1 kinetic energy indicate impulsive energy release during the crash, followed by a reduced and slowly varying kinetic energy level as the system relaxes toward a steady regime, consistent with saturation of the n = 1 dynamics and stabilization of the core current redistribution process. [ABSTRACT FROM AUTHOR]
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  Data: &lt;i&gt;Copyright of European Physical Journal D (EPJ D) is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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