Nonlinear Energetic Particle Transport in the Presence of Multiple Alfvenic Waves in ITER

TL;DR

This study uses advanced nonlinear models to analyze energetic particle transport driven by multiple Alfvenic waves in ITER, revealing complex multi mode interactions and significant radial redistribution effects.

Contribution

It extends previous studies to the ITER scenario, demonstrating the importance of nonlinear effects and multi mode interactions in energetic particle transport.

Findings

Nonlinear effects are crucial for mode evolution in ITER.

Multi mode interactions can cause large amplitude growth.

Radial redistribution exceeds quasi-linear predictions.

Abstract

This work presents the results of a multi mode ITER study on Toroidal Alfven Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main conclusions from earlier studies of ASDEX Upgrade discharges can be transferred to the ITER scenario: global, nonlinear effects are crucial for the evolution of the multi mode scenario. This work focuses on the ITER 15 MA baseline scenario with with a safety factor at the magnetic axis of $q_0 =$ 0.986. The least damped eigenmodes of the system are identified with the gyrokinetic, non-perturbative LIGKA solver, concerning mode structure, frequency and damping. Taking into account all weakly damped modes that can be identified linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior: while in some parameter range, quasi-linear estimates turn out to be reasonable approximations for the nonlinearly relaxed energetic particle profile, under certain conditions low-n TAE branches can be excited. As a consequence, not only grow amplitudes of all modes to (up to orders of magnitude) higher values compared to the single mode cases but also, strong redistribution is triggered in the outer radial area between $\rho_\mathrm{pol} =$ 0.6 and 0.85, far above quasi-linear estimates.