Speaker
Limin Yu
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1055.pdf
Low-frequency fishbone driven by passing fast ions in Tokamak plasmas
Limin Yu1 , Feng Wang2 , G. Y. Fu3
1 Department of Physics, East China University of Science and Technology, Shanghai, China
2 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of
Education), School of Physics, Dalian University of Technology, Dalian, China
3 Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China
The internal kink modes with dominant poloidal and toroidal wave number m = 1 and n =
1 can be strongly destabilized by both the perpendicular and tangential neutral-beam injec-
tion [1, 2]. With perpendicular injection, the driven modes can be considered as either an
energetic particle mode (EPM) with mode frequency comparable to the toroidal precession
frequency of the trapped energetic ion [3] or a "gap" mode with mode frequency close to the
thermal ion diamagnetic frequency [4]. With tangential injection, both the high-frequency mode
and the low-frequency mode have been observed [2]. For the high-frequency branch, the mode
was considered as an EPM with frequency determined by energetic particle toroidal circulation
frequency [5, 6]. For the low-frequency branch, the mode was modeled as a "gap" mode with
the thermal ion diamagnetic frequency [7]. In this work, within the framework of the theory of
EPM, the low-frequency mode driven by a resonant interaction between the passing beam ions
and the wave with ω = ωφ − ωθ is studied, where ωφ and ωθ are respectively the circulation
frequency in toroidal and poloidal direction of passing fast ions. With the effect of finite orbit
width (FOW) of fast ions, the instability can be excited by passing fast ions. It is found that
magnetic shear at the q=1 radius plays an important role in the instability whereas the effect of
the background plasma beta is weak. In particular, there exists a critical magnetic shear below
which the beam ion beta threshold for EPM excitation is very small. For moderate or higher
magnetic shear the beam ion beta threshold is about a few percent. These results are consistent
with experimental observation of the low-frequency fishbone in the HL-2A tokamak [8].
References
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[2] W. W. Heidbrink, et al., Phys. Rev. Lett. 57, 835 (1986)
[3] Liu Chen, et al., Phys. Rev. Lett. 52, 1122 (1984)
[4] B. Coppi, F. Porcelli, Phys. Rev. Lett. 57, 2272 (1986)
[5] Shaojie Wang, Phys. Rev. Lett. 86, 5286 (2001)
[6] Feng Wang, et al., Nucl. Fusion 57, 056013 (2017)
[7] R. Betti, J. P. Freidberg, Phy. Rev. Lett. 70, 3428 (1993)
[8] Liming Yu, et al, J. Phys. Soc. Jpn. 86, 024501 (2017)
