Speaker
Zhiyong Qiu
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1074.pdf
Gyrokinetic theory of toroidal Alfvén eigenmode nonlinear saturation via
ion Compton scattering
Z. Qiu1 , L. Chen1,2 and F. Zonca3,1
1 Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027, P.R.C.
2 Dept. Physics and Astronomy, Univ. of California, Irvine CA 92697-4575, U.S.A.
3 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Frascati (Roma), Italy
Shear Alfvén wave instabilities such as toroidal Alfvén eigenmode (TAE) [1] are expected
to play important roles in magnetic confinement fusion devices as energetic particles (EPs)
contribute significantly to the total power density [2, 3]. TAE can be driven unstable by EPs,
and in turn, induce EP transport and degrade overall plasma confinement.
In this work, the TAE frequency cascading via ion Compton scattering and saturation due to
enhanced coupling to SAW continuum, originally investigated in Ref. [4] in the long wavelength
MHD limit, is extended to the burning plasma relevant short wavelength regime [3]. The equa-
tion describing a test TAE nonlinear evolution due to interacting with the bath of background
TAEs is derived using gyrokinetic theory, which is then applied to deriving the wave-kinetic
equation for the TAE spectrum evolution in the continuum limit. The wave-kinetic equation is
solved to obtain the saturation spectrum of TAE, yielding an overall fluctuation level lower than
the estimation by drift kinetic theory [4], as a consequence of the enhanced nonlinear couplings
in the short wavelength limit [5]. The bulk ion heating rate from nonlinear ion Landau damp-
ing is also calculated. Our theory also shows that, for TAE saturation in the parameter range
of practical interest, several processes with comparable scattering cross sections can be equally
important.
References
[1] C. Z. Cheng, L. Chen and M. S. Chance, Ann. Phys. 161, 21, (1985).
[2] M. Rosenbluth and P. Rutherford, Phys. Rev. Lett. 34, 1428 (1975).
[3] L. Chen and F. Zonca, Rev. Mod. Phys. 88, 015008, (2016).
[4] T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266, (1995).
[5] Z. Qiu, L. Chen and F. Zonca, Nuclear Fusion 57, 056017, (2017).
