Unveiling non-flat profiles within magnetic islands in tokamaks.

The presence of non-flat profiles on magnetic island is studied for the first time through gyrokinetic simulations alongside a simplified Lagrangian model. We have identified that inside a magnetic island, the non-flatness of density and temperature profiles is controlled by a dimensionless parameter α ≡ w * s ̂ ϵ / q ρ * , which is a function of normalized island width w * = w / a 0 , magnetic shear s ̂ , inverse aspect ratio ϵ = a 0 / R , safety factor q, and normalized gyroradius ρ * = ρ / a 0 . The gyroradius ρ * dependence of the control parameter α leads to a species-selective transition of profiles from flat to concave only for electrons having high α ∼ O (1). The finding elucidates that electron profiles tend to increasingly deviate from the flat state for a larger magnetic island, in contrast to the conventional wisdom. [ABSTRACT FROM AUTHOR]