Quasi-Linear Simulation of Energetic Ion Relaxation in ITER Mediated by Alfvén Instabilities*

A critical issue for burning plasmas of whether high energy fusion

products or auxiliary heating fast ions will be confined sufficiently

long to compensate for thermal plasma energy losses is addressed.

This issue is mediated by the instability of low, sub-cyclotron frequency Alfven

eigenmodes (AEs) in ITER steady-state scenario. Using a recently

revisited quasi-linear treatment of EP relaxation dynamics in the

presence of AEs we apply it to ITER steady state conditions. We have

found that although the resulting fast ion transport remains modest if

classical particle slowing down is assumed. We report on AE dynamics

utilizing several tools: the comprehensive linear stability study of

the sub-cyclotron Alfvenic spectrum computed by the ideal MHD

NOVA simulations, drift kinetic NOVA-C

calculations for wave-particle interaction and AE growth/damping

rates, and eventually the predictive quasi-linear modeling code RBQ to

assess the EP relaxation on the equilibrium time scale [N.Gorelenkov

et al., PLA'21]. The applications of RBQ in its 2D version have shown

that the AE amplitudes remain relatively low, deltaB/B < 0.003, for

all 42 analyzed unstable TAE modes. We have identified a potentially

important effect of AEs on EP confinement in ITER which is due to EP

depletion near the plasma center. This effect is connected with the

beam ion and fusion alpha particle current drives which is expected to

be also depleted near the center.