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Author: Hongpeng Qu
Requested Type: Pre-Selected Invited
Submitted: 2019-02-20 22:22:27
Co-authors: Feng Wang, Xiaodong Peng, Jiquan Li, Aike Wang
Contact Info:
Southwestern Institute of Physics
No.3,3rd Section, South of 2nd
Chengdu, Sichuan 610041
P R China
Abstract Text:
Magnetic islands generated by tearing instability can induce anomalous transport and degrade plasma confinement, especially in the tokamak experiments. Although attracting much interest in past decades, some basic physics about the NTMs is still under debates, such as the reduction of the neoclassical current contributions to small NTM island evolution.
Here, we analytically discussed the neoclassical polarization current contribution to NTM evolution by solving the ion drift-kinetic equation in a so-called ion-banana-center coordinate system without the past assumption of the large island width. The corresponding results show that, when island width is comparable to the finite-banana-width (FBW) of thermal trapped ion, the neoclassical polarization current term in the equation of the NTM island evolution is much smaller than the previously analytical expression, but matches the empirical anticipation with FBW effect included. In other words, our results suggest that the neoclassical polarization current contribution to the evolution of small islands is not strong as previous expectation. We also investigate the ion bootstrap current distribution in the region of islands analytically and by GTC code. The analytical results indicate that the contribution from ion bootstrap current to NTM evolution is not weakened so much by FBW effect alone. The simulation results show that, when the island width is small, the recovery of the pressure gradient may determine the reduction of the bootstrap current contribution. These works are helpful to understand the threshold mechanism of NTMs.
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