Nonlinear excitations of zonal structures by toroidal Alfvén eigenmodes.

Area of Science:

• Plasma Physics
• Fusion Energy
• Nonlinear Dynamics

Background:

• Zonal flows and structures are key to self-regulating microscopic drift-wave turbulence.
• Toroidal Alfvén eigenmodes (TAEs) are critical in Alfvén wave instabilities within burning fusion plasmas.

Purpose of the Study:

• To investigate the influence of zonal flows and structures on the nonlinear dynamics of TAEs.
• To understand the spontaneous excitation mechanisms of zonal structures driven by TAEs.

Main Methods:

• Nonlinear simulations incorporating trapped-ion responses.
• Inclusion of plasma equilibrium geometry and kinetic thermal ion treatment.

Main Results:

• Finite amplitude TAEs can spontaneously excite zonal structures, driven by trapped-ion responses.
• These zonal structures are predominantly characterized by zonal currents, rather than traditional zonal flows.
• The simulations highlight the importance of plasma geometry and kinetic thermal ions for accurate modeling.

Conclusions:

• Zonal structures, particularly zonal currents, play a significant role in the nonlinear behavior of TAEs in fusion plasmas.
• Accurate simulations require careful consideration of plasma equilibrium geometry and kinetic effects of thermal ions.
• This research provides insights for interpreting experimental observations of zonal fields in fusion devices.