Speaker
Peiwan Shi
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1036.pdf
Beta induced Alfvén Eigenmode Driven by Energetic Ions on HL-2A
P.W. Shi1, W. Chen1, Z. B Shi1, X.R. Duan1
1
Southwestern Institute of Physics, Chengdu, China
Beta induced Alfvén eigenmode (BAE) has become a major concern since the first
observation on DIII-D [1]. Those weak damping modes often enhance transports and cause
substantial reductions of EPs [2]. To better understand the instabilities, more experimental
evidences should be needed. In the present paper, the energetic ions induced BAEs (i-BAEs)
on HL-2A will be given. The i-BAEs are driven by the passing particles with energy of
15-45keV and the mode frequencies are about 60-90kHz. A typical example is shown as
Fig.1(a). The radial mode structure can be measured by the microwave reflectometer with
working frequency of 34-48GHz and it is localized in the region of ρ = 0.1 − 0.25. The
i-BAE has been finally confirmed by the Alfvén mode code (AMC) [3]: the eigenfrequency
of 90kHz is in accordance with the experimental observation and the mode structure agrees
well with that measured by the microwave reflectometer. The i-BAEs can be excited more
easily in low electron density discharges because ion Landau damping is relatively weak in
those cases. Both stationary and non-stationary i-BAEs can be observed during NBI heating.
The ion temperature and neutron count decline obviously when the non-stationary i-BAEs
appear, which suggests a badly deterioration of the plasma confinement. Finally, the mode
frequency is found to be modulated by electron cyclotron resonance heating (ECRH), which
indicates the ECRH may be an effective candidate for the suppression of i-BAEs.
Fig.1 (a) Stationary i-BAE and (b) the corresponding mode structure detected by microwave reflectometer. (c)The
q profile and Alfvén continuum for stationary i-BAE with n=2. (d) The radial mode structure given by the AMC.
Reference
[1] W. W. Heidbrink et al. Phys. Rev. Lett.71, 855 (1993)
[2] L. Chen and F. zonca, Rev. Mod. Phys. 88, 015008 (2016).
[3] H. S. Xie et al Phys. Plasmas 22, 022518 (2015)
