학술논문
I-mode investigation on the Experimental Advanced Superconducting Tokamak
Document Type
Working Paper
Author
Feng, X.; Liu, A. D.; Zhou, C.; Liu, Z. X.; Wang, M. Y.; Zhuang, G.; Zou, X. L.; Wang, T. B.; Zhang, Y. Z.; Xie, J. L.; Liu, H. Q.; Zhang, T.; Liu, Y.; Duan, Y. M.; Hu, L. Q.; Hu, G. H.; Kong, D. F.; Wang, S. X.; Zhao, H. L.; Li, Y. Y.; Shao, L. M.; Xia, T. Y.; Ding, W. X.; Lan, T.; Li, H.; Mao, W. Z.; Liu, W. D.; Gao, X.; Li, J. G.; Zhang, S. B.; Zhang, X. H.; Liu, Z. Y.; Qu, C. M.; Zhang, S.; Zhang, J.; Ji, J. X.; Fan, H. R.; Zhong, X. M.
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Subject
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Abstract
By analyzing large quantities of discharges in the unfavorable ion $ \vec B\times \nabla B $ drift direction, the I-mode operation has been confirmed in EAST tokamak. During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode. Similar with the I-mode observation on other devices, the $ E_r $ profiles obtained by the eight-channel Doppler backscattering system (DBS8)\cite{J.Q.Hu} show a deeper edge $ E_r $ well in the I-mode than that in the L-mode. And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm. WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the $ E_r $ fluctuation and the caused flow shear from WCM should play an important role during I-mode. In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared. Many evidences show that the a low-frequency oscillation may be a novel kind of limited cycle oscillation but further investigations are needed to explain the new properties such as the harmonics and obvious magnetical perturbations.
Comment: 14 pages, 7 figures
Comment: 14 pages, 7 figures