Experimental investigations on physical mechanisms of RMP-induced intrinsic rotations at EAST
Authors: Jin Yi-Fei , Zhang Hong-Ming , Yin Xiang-Hui , Lü Bo , Cheonho Bae , Ye Kai-Xuan , Sheng Hui , Wang Shi-Fan , Zhao Hai-Lin , Gu Shuai , Yuan Hong , Lin Zi-Chao , Fu Sheng-Yu , Lu Di-An , Fu Jia , Wang Fu-Di ,   Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China,   Science Island Branch, Graduate School of University of Science and Technology of China, Hefei 230026, China,   School of Electrical Engineering, University of South China, Hengyang 421001, China,   Enn Science and Technology Development Co., Ltd., Langfang 065001, China,   School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026, China,   School of Nuclear Science and Technology, University of South China, Hengyang 421001, China
Published: November 2024

Plasma spontaneous rotation significantly affects confinement performance and stability in tokamaks. Effectively inducing this rotation is essential for stabilizing resistive wall modes (RWMs) and ensuring the stable operation of the International Thermonuclear Experimental Reactor (ITER). Recent experiments conducted on the Korea Superconducting Tokamak Advanced Research (KSTAR) device demonstrated that resonant magnetic perturbations (RMPs) can induce neoclassical toroidal viscosity (NTV) torque under certain conditions, successfully driving plasma rotation. Similarly, on the Experimental Advanced Superconducting Tokamak (EAST), an increase in plasma rotation in the direction of the plasma current has been observed following RMP application. However, unlike the KSTAR findings, the NTV torque simulations for EAST are two orders of magnitude lower than experimental measurements, indicating additional mechanisms beyond NTV may drive the observed plasma rotations. In this paper, to investigate these mechanisms, momentum balance, causality, and statistical analyses are performed at EAST. An increase in rotation velocity is found to correlate with significant changes in the <inline-formula><tex-math id="M4">\begin{document}${\boldsymbol{E}}\times{\boldsymbol{B}}$\end{document}</tex-math></inline-formula> flow, matching the RMP-induced torque distribution. This alignment suggests that residual stress, arising from variations in <inline-formula><tex-math id="M5">\begin{document}${\boldsymbol{E}}\times{\boldsymbol{B}}$\end{document}</tex-math></inline-formula> shear, may cause the observed rotation to increase. The effects of stochastic fields on multi-scale turbulence are considered as a possible explanation for correlations between <inline-formula><tex-math id="M6">\begin{document}${\boldsymbol{E}}\times{\boldsymbol{B}}$\end{document}</tex-math></inline-formula> velocity and toroidal rotation. Stochastic fields appear to enhance the inertia of large-scale turbulence while driving small-scale turbulence to maintain quasi-neutrality. The resulting turbulent Reynolds stress, generated by small-scale turbulence, may account for the increases of the observed <inline-formula><tex-math id="M7">\begin{document}${\boldsymbol{E}}\times{\boldsymbol{B}}$\end{document}</tex-math></inline-formula> velocity during RMP application. Statistical analysis further highlights the importance of island width in understanding the threshold RMP current in ramping-up RMP experiments, supporting the conclusion that turbulence-driven <inline-formula><tex-math id="M8">\begin{document}${\boldsymbol{E}}\times{\boldsymbol{B}}$\end{document}</tex-math></inline-formula> shear-related residual stress is the key mechanism of driving plasma rotation following RMP application.