Radial localization of toroidicity-induced Alfvén eigenmodes

Area of Science:

• Plasma Physics
• Fusion Energy
• Computational Physics

Background:

• Toroidal Alfvén eigenmodes (TAEs) are crucial for understanding plasma stability in fusion devices.
• Magnetohydrodynamic (MHD) theory provides a conventional framework for analyzing these modes.
• The influence of energetic particles (EPs) on TAEs is a key area of research.

Purpose of the Study:

• To investigate the radial localization of TAEs in fusion plasmas.
• To understand the role of nonperturbative energetic particle contributions in TAE behavior.
• To compare simulation results with predictions from conventional magnetohydrodynamic theory.

Main Methods:

• Linear gyrokinetic simulations were employed to model fusion plasma behavior.
• The simulations focused on the effects of energetic particle pressure gradients on TAEs.
• Analysis included mode width, radial position, and frequency dependence on toroidal mode number.

Main Results:

• A significant radial localization of TAEs was observed, driven by nonperturbative EP contributions.
• The EP-driven TAEs exhibited a much smaller radial mode width than predicted by MHD theory.
• TAE radial positions were found to correlate with the strongest EP pressure gradients.
• The nonperturbative EP contribution was identified as the cause for broken radial symmetry in ballooning modes and frequency dependence on toroidal mode number.

Conclusions:

• Energetic particle contributions fundamentally alter TAE behavior, leading to radial localization beyond MHD predictions.
• The findings highlight the limitations of conventional MHD theory in describing EP-driven TAEs.
• This research provides critical insights into plasma stability and transport relevant to magnetic confinement fusion.