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Description
In magnetic confinement fusion plasmas, the confinement performance of α particles is crucial for maintaining steady-state burning plasma. Under classical conditions, α particles heat the bulk plasma through Coulomb collisions, and even considering the toroidal magnetic field structure of tokamaks, the neoclassical transport levels remain low. However, the kinetic effects and spatial gradients of α particles can easily lead to nonlinear interactions with toroidal Alfvén eigenmodes (TAE), significantly altering the confinement level of α particles[1]. Therefore, developing numerical models to understand the impact of TAE on α particle transport is essential for comprehending and optimizing the physics related to α particles. This work employs the particle orbit tracing code PTC developed by our team[2], to analyze α particle transport physics under the influence of TAE. The study is based on the data of the CFETR 2019 steady-state scenario (v20190422)[3], incorporating the TAE structures calculated using the GEM code[4]. Firstly, this study investigates the resonance conditions between TAE and α particles during the linear phase. The α particles are uniformly initialized in the (ψ, μ) phase space at the middle plane of tokamak with E0=3.5MeV. It is found that passing particles within the resonance region experience stronger perturbations compared to resonance trapped particles, thereby identifying the strongest wave-particle resonance relationships. Under high-n TAE perturbations, there are more types of resonances compared to low-n TAE perturbations, and they are distributed more densely. During the nonlinear phase, α particles move radially under TAE perturbations, forming mixed structures in the (Θ, Pφ) phase space. Initially resonant particles eventually drift out of resonance, experiencing phase shifts until the drift of Pφ reverses, leading to island-like structures. Particles far from resonance maintain their phase space trajectories. When the saturation amplitude of the TAE perturbation is enhanced, the adjacent phase-space islands will overlap, which further leads to enhanced transport of α particles. The effect of TAEs on α particles varies with different toroidal mode numbers n. The results show that radial transport of α particles is strongest for the most unstable TAE modes with n=7, 8, 10. This outcome enhances our understanding of nonlinear wave-particle interactions in collisionless plasmas and provides numerical references for mitigating TAE-induced transport of α particles.
[1] Chen L., and Zonca F. Rev. Mod. Phys. 88 015008 (2016).
[2] Feng Wang et al, Chin. Phys. Lett. 38 055201 (2021).
[3] Zhuang G., Li G. Q., Li J. et al. Nucl. Fusion 59 112010 (2019).
[4] Zhen-Zhen Ren et al. Nucl. Fusion. 60 016009 (2020).
| Presentation type | Oral |
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