7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Investigation of alpha particle transport induced by Alfvén eigenmodes inCFETR
Wei Shen1, Zhenzhen Ren2, G. Y. Fu3, Yang Chen4, Jinhong Yang5, Weihua Wang5
1
Institute of Plasma Physics, Chinese Academy of Science2
School of Physics and optoelectronic engineering, Anhui University
3
Institute for Fusion Theory and Simulation and College of Physics, Zhejiang University
4
University of Colorado at Boulder
5
Institutes of Physical Science and Information Technology, Anhui Universitye-mail (speaker): shenwei@ipp.ac.cn

China Fusion Engineering Test Reactor (CFETR) is thenext-generation fusion facility in the roadmap of Chinese
fusion energy development, which aims to bridge the gap
between International Thermonuclear Experimental
Reactor (ITER) and the magnetic fusion energy
demonstration reactor (DEMO). At the moment, one
challenge is the confinement of energetic particles (EPs),
especially the alpha particles produced by the
deuterium-tritium fusion reaction. It has been
demonstrated both theoretically and experimentally that
Alfvén eigenmodes (AEs) can be destabilized byenergetic particles through wave-particle interaction. In
present tokamak devices, it is found that AE activity canflatten the energetic particle profile radially, which may
degrade fusion performance in a reactor. Therefore, it iscrucial to investigate the physical mechanisms of AEs
driven by energetic particles and energetic particle
transport. In this work, we investigate the AE instability
using the hybrid gyrokinetic ion/massless fluid electron
model in GEM code [1] with the latest design parametersof CFETR. In addition, a new simplified energetic
particle transport model based on the resonancebroadened quasi-linear (RBQ) model [2] is developed
and applied to investigate the transport of alpha particles
in CFETR.
In this work, the parameters and equilibrium profiles
according to the latest design of CFETR (steady statescenario) are used. The linear stability of intermediate
toroidal mode number 4 ≤ n ≤ 12 AEs in CFETR issimulated by GEM, and it is found that the toroidal mode
number of the most unstable AE is n=8, which is larger
than those in present tokamaks. Furthermore, According
to Alfvén continuous spectra of n=7,8,9 modescalculated by NOVA, the radial locations of the modes
combined with the mode frequencies relative to Alfvén
spectra indicate that these modes are inside the TAE gaps,
which indicate that these modes are TAEs. The results
indicate that AEs can be driven strongly in CFETR
plasmas.
A simplified alpha particle transport model based on theRBQ model is proposed and applied in this work. If themode frequency is small or the toroidal mode number islarge, the diffusion of energetic particle can be assumed
just in the radial direction. When the dependence on thevelocity space is ignored, the diffusion coefficient can besimplified as D∝γA2, where D is the radial diffusion
coefficient, γ is the mode growth rate, A represents theeffective mode structure in the radial direction. Multiple
iteration steps are applied to calculate the alpha particle
transport in the presence of multiple unstable AEs
according to the transport model, and the iteration
process is shown as follows. Firstly, the diffusion
coefficient is calculated based on the linear growth rates
and mode structures of AEs, which are simulated byGEM with the initial alpha particle density profile, andalpha particle density profile is evolved by solving thediffusion equation. At the next iteration step, were-calculate the linear growth rates and mode structuresof AEs with the updated alpha particle density profile
from the previous iteration step, and evolve alpha density
profile again until reaching a steady state using the
diffusion coefficient corresponding to the updated mode
structures and growth rates. This iteration process isrepeated until the alpha particle density profile is almost
the same with that of the previous iteration step.
Simulation results using the reduced transport modelshow that, due to multiple unstable AEs, the alphaparticle density decreases in the core and alpha particles
are transported from the core region to the outer region.
We find that the minimum value of the safety factor
and the central beta value of alpha particle havesignificant effects on the alpha particle transport, and theAE-induced alpha particle transport level becomes lower
with smaller linear growth rates. In addition, it is foundthat the transport level and radial range of theredistributed alpha particle density profile depend on theradial location.
This work is supported by National Key R&D Programof China under Grant Nos. 2019YFE03050002 and2022YFE03040002, the National Natural Science
Foundation of China under Grant Nos. 12005003 and11975270, and Science Foundation of Institute of Plasma
Physics, Chinese Academy of Sciences under Grant No.
DSJJ-2022- 04.
References[1] Y. Chen et al, Phys. Plasmas 20, 092511 (2013)[2] N. Gorelenkov et al, Nucl. Fusion 58, 082016 (2018)