Unveiling non-flat profiles within magnetic islands in tokamaks

Abstract

<jats:p>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*ŝϵ/qρ*, which is a function of normalized island width w*=w/a0, magnetic shear ŝ, inverse aspect ratio ϵ=a0/R, safety factor q, and normalized gyroradius ρ*=ρ/a0. 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.</jats:p>