18th Technical Meeting on Energetic Particles in Magnetic Confinement Systems

Calculation of toroidal Alfvén eigenmode mode structure in general axisymmetric toroidal geometry

Not scheduled

20m

Collective Phenomena

Speaker

Guangyu Wei (Zhejiang University)

Description

Abstract: A workflow is developed[1] based on the ideal MHD equations to investigate the linear physics of various Alfvén eigenmodes in general axisymmetric toroidal geometry by solving the coupled shear Alfvén wave (SAW) and ion sound wave (ISW) equations[2,3] in ballooning space. The model equations are solved by FALCON code[4] in the singular layer, and the corresponding solutions are then taken as the boundary conditions for determining the mode frequency and calculating the parallel mode structures in the whole ballooning space.
As an application of the code, the frequency and mode structure of toroidal Alfven eigenmode (TAE) are calculated in a reference equilibrium of the Divertor Test Tokamak facility (DTT)[5], uncovering the existence of a finite damping rate and radial singular structure of TAE due to the coupling with acoustic continuum, although the damping rate is generally small for typical parameters. As another application, we calculate TAE frequencies and mode structures in the equilibria with different triangularities and demonstrate that the effect of triangularity on TAE is normally weak within the ideal MHD description adopted. Our calculation implies that the potential effect of (negative) triangularity on TAE may result from the modification of the wave-particle resonant condition [6]. The code workflow has recently been extended to handle the kinetic response of energetic particles in general geometry by adopting the action angle approach[7]. Based upon this formulation, we are further exploring the instability of TAE driven by energetic particles.

Key words：eigenvalue code, ideal MHD, toroidal Alfvén eigenmode, triangularity

References：
[1] G. Wei, M. V. Falessi, T. Wang, F. Zonca, and Z. Qiu, Phys. Plasmas 31, 072505 (2024).
[2] F. Zonca and L. Chen, Phys. Plasmas 21, 072120 (2014).
[3] L. Chen and F. Zonca, Phys. Plasmas 24, 072511 (2017).
[4] M. V. Falessi, N. Carlevaro, V. Fusco, G. Vlad, and F. Zonca, Phys. Plasmas 26, 082502 (2019).
[5] R. Albanese and A. Pizzuto (WPDTT2 Team and DTT Project Proposal Contributors), Fusion Eng. Des. 122, 274 (2017).
[6] P. Oyola et al., 29th IAEA Fusion Energy Conference (2023).
[7] F. Zonca, L. Chen, S. Briguglio, G. Fogaccia, G. Vlad, and X. Wang, New J. Phys. 17, 013052 (2015).