Alpha particle confinement in CFEDR H-mode scenario

The alpha particle confinement in the CFEDR H-mode scenario is investigated. It is found that, within engineering limitations, 500 mm ferromagnetic insert can reduce the alpha particle and power loss caused by magnetic ripples to 1% and 0.65%, respectively, leading to an acceptable 0.1 MW/m² peak heat load on the outboard mid-plane of plasma facing components. Global gyrokinetic simulations show that multiple toroidal Alfvén eigenmodes (TAEs) with toroidal mode number n ~ 20−40 can be driven marginally unstable by alpha particles in the core region, with \gamma/\omega_\mathrmr\leqslant 2%. Here, \gamma is the linear growth rate, and \omega_\mathrmr is the mode frequency. Multiple- n nonlinear simulations show that TAEs saturate at a low saturation level, that lead to a negligible alpha particle diffusion rate D_\textα ~ 0.06 m²/s. Fishbone is shown to be unstable in the present scenario, which may lead to weak radial redistribution of alpha particles, with the dominant contribution from magnetically trapped particles.