# Numerical study of transition between even and odd toroidal Alfv\'en eigenmodes on EAST

## TL;DR

This study uses linear simulations with the NIMROD code to analyze the behavior and transition of toroidal Alfvén eigenmodes driven by energetic particles on EAST, revealing mode structure changes and coexistence near thresholds.

## Contribution

It presents the first detailed simulation of TAE mode transitions on EAST using the hybrid-kinetic MHD model, linking energetic particle beta fraction to mode structure changes.

## Key findings

- Mode transition between even and odd TAEs identified.
- Mode structure changes from ballooning to anti-ballooning near thresholds.
- Coexistence of different TAE types observed at transition points.

## Abstract

Linear simulations of toriodal Alfv\'en eigenmodes (TAEs) driven by energetic particles (EPs) on EAST (Experimental Advanced Superconducting Tokamak) are performed using the hybrid-kinetic MHD (HK-MHD) model implemented in NIMROD code. The EAST equilibrium is reconstructed using the EFIT code based on experimental measurement. The "slowing down" distribution is adopted for modeling the equilibrium distribution of the energetic ions from the deuterium neutral beam injection on EAST. The frequency, the dominant poloidal mode number, the radial location and the detailed 2D mode structure of the TAE/RSAE/EPM modes are consistent between the eigenvalue analysis and the NIMROD simulation. As the $\beta$ fraction of EP increases, a transition between even and odd TAEs occurs, along with that between the ballooning and anti-ballooning mode structures. When the $\beta$ fraction of EP is close to the transition threshold, both types of TAEs coexist.