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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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Bibliographic Details
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]
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Database:	Engineering Source

Description
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]
ISSN:	14346060
DOI:	10.1140/epjd/s10053-026-01168-1