Speaker
Haijun Ren
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1031.pdf
Geodesic Acoustic Mode Driven by Energetic Particles with bump-on-tail
distribution
Haijun Ren1 and Hao Wang2
1 CAS Key Laboratory of Geospace Environment and School of Physical Sciences, University
of Science and Technology of China, Hefei 230026, P. R. China
2 National Institute for Fusion Science, Toki 509-5292, Japan
Energetic-particle-driven geodesic acoustic mode (EGAM) is analytically investigated by
adopting the bump-on-tail distribution for energetic particles (EPs), which is created by the
fact that the charge exchange time (τcx ) is sufficiently shorter than the slowing down time (τsl ).
The equilibrium distribution of EPs is proportional to (E 3/2 + Ec )τs −1 , where E is the kinetic
3/2
energy of EPs and Ec is the critical one. For τs = 0, the distribution is reduced to the slowing-
down model.
The dispersion relation is derived in the use of
gyro-kinetic equations. The ratio of critical energy kHz
70
Ec to the inertial energy E0 is generally considered 60
to be less than unit for theoretical study, while in 50
Frequency
40 Growth rate
the realistic experiments or relative simulation, the 30
Frequency (MEGA)
Growth rate (MEGA)
= 20.4/3
ratio can be up to 0.35, leading to remarkable ef- 20
s
10
fects. Similar to the slowing-down model, there are 0
three branches of EGAM. We concentrate only on 0.0 0.2 0.4 0.6
the unstable branch. Following relative simulation
and experimental work, we specifically considered Figure 1: The real frequency (solid curve)
two cases: τsl /τcx = 3.4 and τsl /τcx = 20.4. The and growth rate (dashed one) versus the pitch
pitch angle is shown to significantly enhance the angle for τs = 20.4/3. The density ratio εh =
growth rate and meanwhile, the real frequency is 0.3 is adopted. The major radius R0 = 3.9m
dramatically decreased with increasing pitch angle. is used as done in the simulation [1]. In the
The excitation of high-frequency EGAM is found, right part, the MEGA simulation dates are
and this is consistent with both the experiment and cited from Fig. 10 in Ref. [1].
the simulation.
References
[1] H. Wang et al, Phys. Plasmas 22, 092507 (2015).
[2] G. Fu, Phys. Rev. Letts. 101, 185002 (2018).
[3] N. Winsor, J. L. Johnson and J. M. Dawson, Phys. Fluids 11, 2448 (1968).
